Muller, Christopher

Christopher Muller is a speaker at WEFTEC 2026.

Titles from this speaker

A Surveillance Study: Per-and polyfluoroalkyl Substances (PFAS) in Biosolids

Abstract

This surveillance study was aimed at understanding concentrations of PFAS in biosolids. To address this objective, samples were collected from of twenty-five wastewater resource recovery facilities (WRRFs) throughout North America over a six-month period. A minimum of two samples were collected from each WRRF: Location A – sludge entering the stabilization process, and Location B – biosolids (post-stabilization sludge). Modified EPA Method 537.1 was used to analyze 40 PFAS compounds in these samples by Eurofins Laboratories. Only 20% of the measured PFAS compounds were detected in the biosolids samples. Three major solid stabilization methods were evaluated, anaerobic digestion, incineration, and chemical stabilization. Anaerobic digestion and chemical stabilization indicated increases in PFAS in Location B in comparison to Location A, except for in the case of incineration, where ash samples (Location B) did not contain any of the measured PFAS compounds above the method detection limit.

Per-and polyfluoroalkyl Substances (PFAS) are being extensively studied in all the matrices due to their ubiquitous presence in the environment and negative human health impacts. This study conducted a survey of twenty-five wastewater resource recovery facilities (WRRF) throughout North America over a six-month period to evaluate for PFAS other emerging contaminants in biosolids. Among the 40 PFAS compounds evaluated, only 20% were detected in biosolid samples. Concentrations of the detected PFA

SpeakerOza, Shubhashini

Presentation time

13:30:00

13:55:00

Session time

13:30:00

15:00:00

SessionUnderstanding and Addressing PFAS in Biosolids

Session locationRoom N426b - Level 4

TopicMunicipal Wastewater Treatment Design, PFAS

Author(s)

Oza, Shubhashini

Author(s)S. Oza 1; S. Estahbanati 2 ; J. Norton 3; N. Hontoria 4; X. Fonoll Almansa 5; M. Khan 6; C. Muller 7; K. Bell 8; J. Hatfield 4; S. Oza 1;

Author affiliation(s)Brown & Caldwell 1; Brown & Caldwell 2 ; Great Lake Water Authority 3; Brown & Caldwell 4; Great Lake Water Authority 5; Great Lake Water Authority 6; Brown & Caldwell 7; Brown & Caldwell 8; Brown & Caldwell 4; Brown & Caldwell 1;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2023

DOI10.2175/193864718825159011

Volume / Issue

Content sourceWEFTEC

Word count10

Description: Acid+ A Novel Treatment Process Configuration for Simultaneous Process...

Acid+ A Novel Treatment Process Configuration for Simultaneous Process Intensification and Struvite Management

Abstract

Acid/gas anaerobic digestion process is based the premise of environmental phasing, such that the conditions with the digestion process are first optimized for hydrolysis, acidogenesis and acetogenesis followed by a methanogenic phase for conversion of the solubilized organics to methane. The City of Columbus Southery WRF in Columbus, OH has operated an acid/gas system for more than a decade, treating a mixture of primary and secondary sludge. Over this period of time the City has conducted research surrounding improving process stability and reliability. One factor that has played a significant role in the operational reliability of the process, for Columbus, is the operation of the acid phase digestion. Reducing the acid phase operation to 1.8 days or less eliminated chronic foaming in the methane phase with the addition of thickened waste activated sludge. The addition of TWAS to the digestion process, reduced the solids disposal costs but increased the production of struvite, which fouls dewatering equipment and return lines. Acid reactors or fermenters have demonstrated very effective release of phosphorus from sludge. This likely make struvite production from the digestion process at Columbus a magnesium limited system. Based on operating observations, there is sufficient magnesium in the water to create a nuisance levels of struvite in the system. Concurrent with the struvite issues, there is a desire on the City's part to better understand the process limits and increase capacity, as Southerly moves into a facilities expansion project. Based on these operational issues, process interests and an impending capital program Columbus wanted to explore the novel process concept of Acid+, a process flow of which is shown in Figure 1. Acid+, modifies a base acid/gas system through the addition of a harvesting digester and recuperative thickening on the methane phase digesters. The harvesting digesters are designed to create an environment where struvite precipitation can be forced and managed. By recycling a flow of neutral pH sludge to the incoming acidified sludge and adding magnesium hydroxide the conditions are set for struvite formation. Using a high-rate gas mix system creates the micro-environment where pH is further increased and granular struvite can be formed, collected and harvested, as show in Figure 2. A collaborative research project was created between the City of Columbus, NYCDEP, University of Massachusetts- Amherst and City College of New York and Brown and Caldwell with funding provided by the Water Research Foundation under project WRF-5108. The project plan looks to understand the different process elements of Acid+, in sequence, such that a controlled approach process evaluation could be conducted. The phase 1 work focused on optimization of the acid phase both in batch and continuous operation, phase 2 looks to evaluate the continuous operation of acid/gas with the findings of phase 1 and then finally phase 3 would integrate the harvesting reactor on the optimized acid gas system, creating an Acid+ configuration. The phase 1 work is complete and the phase 2 is on-going. Figure 3,4 and 5 summarizes the influence of temperature and sludge type on key factors to struvite control for acid plus and overall acid phase digester performance. The fermentation/acidification process, as shown in Figure 4, demonstrates that temperature primarily impacted the rate of acidification, as measured by total VFA. This observation while not unexpected, did also show that the extent of conversion, maximum VFA produced did not appreciably change over the course of the full study period. This suggests that from an intensification strategy, temperature elevation can successfully deployed to reduce reactor size or increase throughput without a loss in performance. However, the degree of acidification achieved will be very sludge specific, for waste activated sludges. This would suggest that the sludge composition and/or biology has an influence of the acidification process. This is demonstrated by the shape of the acid production curves, with different sludges having different rates and time to onset of VFA production. This also holds true for both ammonia release and phosphorus release. Thermophilic operation appears to provide significant benefit to both. A key consideration for Acid+ would be the impact of operating at thermophilic temperatures and and need to reduce temperature to improve struvite precipitation. Based on these data it could be assumed that the treatment process would impact that performance, however when secondary treatment type was considered there was not a clear correlation. Other actors such as EPS content and metals may be influencing the performance as well as wastewater source. These will be explored in greater detail. In the associated paper.

This paper was presented at the WEF Residuals and Biosolids Conference, June 18-21, 2024.

SpeakerMuller, Christopher

Presentation time

16:15:00

16:45:00

Session time

15:45:00

16:45:00

SessionNutrient Management Innovations

Session number20

Session locationOklahoma City Convention Center, Oklahoma City, Oklahoma

TopicAdvanced Treatment, Anaerobic Digestion, Struvite

Author(s)

Muller, Christopher

Author(s)C. Muller1, A. Abouhend2, C. Park2, D. Fiorino1, N. Perez3, K. Ramalingam4, J. Willis1, G. Schweinfurth5, A. Dhanasekar6

Author affiliation(s)Brown and Caldwell 1; University of Massachusetts 2; Brown and Caldwell 1; NYCDEP 3; The City College of New York 4; Brown and Caldwell 1; City of Columbus 5; The Water Research Foundation 6;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Jun 2024

DOI10.2175/193864718825159469

Volume / Issue

Content sourceResiduals and Biosolids Conference

Word count14

Application of Vacuum Extraction to Anaerobic Digestion for Process Intensification and Resource Recovery

Abstract

The IntensiCarbTM process utilizes the decoupling of SRT and HRT, like recuperative thickening, to increase process capacity while simultaneously reducing the influence of toxic metabolic by products through extraction (ex. ammonia-N) and recover additional methane. This paper summarizes 3 years of research evaluating the efficacy of the process utilizing a side-by-side comparison of conventional mesophilic digestion with varying intensification factors (2x, 3x, 4x, 5x) in bench-scale trials conducted at Western University in London, Ontario digesting blend of primary and secondary sludge collected from the Greenway Wastewater Treatment Plant. Figure 1 provides a process flow diagram of the IntensiCarbTM process simulated in these tests. Figure 2, plots change in volatile solids reduction (VSr) in relation to hydraulic and solids retention times of IntensiCarb to explore its impact on the rate and extent of digestion. Based on this data it can be seen that the primary mechanism of process enhancement is the rate of digestion, rather than extent, being able to operate a higher loading rate, low HRT, with out significant increase in overall destruction at extended SRT. While some instability was observed in the higher loading rates it was transient during transition periods. With the move toward resource recovery, the energy yield of the digestion process is as critical as maximizing methane production per unit volume has potential long-term operating cost benefits as well as sustainability impacts. Figure 3, plots the impact of digester hydraulic retention time on the methane yield of the digester (m3-CH4/m3digester/d). Figure 3, clearly illustrates that with the IntensiCarbTM process the methane yield on an equivalent digester volume basis is more than 4.5 times higher than the conventional digester at 20 days SRT; 1.28 m3-CH4/m3digester/d verses 0.28 m3-CH4/m3digester/d, respectively. Furthermore, conventional mesophilic digestion typically does not operate, at scale, under 15 days of retention time. This is because below this level significant risk to process stability has been historically observed. The accumulation of ammonia has a self-limiting effect on anaerobic digestion. To date, no technology has effectively managed ammonia-N in-situ, resulting in risks for process instability and or significant population shifts, as reported by Mah et al. (2017) for THP. This is significant in that the control of ammonia in the digester could support high loadings without the negative impacts of toxicity and reduce return stream impacts, often a concern with high rate anaerobic digestion processes. The data shows (Figure 4) that as the digester load increased with IntensiCarbTM, the overall total ammonia-N levels remained around 800 mg-N/L or less, while a more conventional system would be expected to be operating at 2,100 to >5,000 mg-N/L. This observation alleviates one of the primary limits to anaerobic digestion. High loadings and high ammonia concentrations have been attributed to shifts in digester populations, as outlined by Mah et al (2017) when evaluating thermal hydrolysis. With similarly high loads but significantly reduced ammonia-N levels, the population profile of several of the test digesters were evaluated and compared to the control. The relative abundance of bacteria and archaea (methanogens) depicted in Figure 6 indicates that the relative abundance of archaea increases with intensification factor, approximately 40% (Figure 5). Looking at the specific methanogenic population present, there is a shift that occurs between the conventional (Control) digester relative to the intensified digesters. As the intensification level increases the methanogenic population shifts from one dominated by the low-growth rate Methanosaeta to one dominated by high-growth rate Methanosarcina (Figure 6). Some have suggested that digesters dominated by Methanosarcina have a higher overall capacity and stability due to their significantly higher maximum specific growth rate. The opposite was reported for thermal hydrolysis based digestion (Mah et al (2017)). Vacuum enhanced anaerobic digestion represents a novel process for the intensification of anaerobic sludge stabilization. Potentially offering unique opportunities for resource recover, ammonia-N and dissolved methane, as well as providing a mechanism to alleviate the current limitations associated with anaerobic digestion, metabolic byproduct toxicity.

The IntensiCarbTM, process is a vacuum enhanced anaerobic digestion process, that separates solids and hydraulic residence time. Resulting in increased process capacity by six times and in-situ removal of ammonia from the digestion process, exceeding the capacity of all commercially available sludge digestion processes on the market today. The process appears to select for increased methanogenic robustness and ammonia tolerance as well as create new opportunities for resource recovery.

SpeakerMuller, Christopher

Presentation time

16:00:00

16:20:00

Session time

15:30:00

17:00:00

SessionAdvances in Anaerobic Digestion

Session number219

Session locationRoom 344

TopicBiosolids and Residuals, Intermediate Level, Research and Innovation

Author(s)

Muller, Christopher, Khadir, Ali, Abdelrahman, Amr, Al-Omari, Ahmed, Jang, Eunkyung, Bell, Katherine, Norton, John, Sheculski, Chris, Santoro, Domenico, Nakhla, George

Author(s)C. Muller1, A. Khadir3, A. Abdelrahman3, A.A. Al-Omari1, E. Jang2, K. Bell1, J. Norton4, C. Sheculski2, D. Santoro2, G.F. Nakhla3

Author affiliation(s)1Brown and Caldwell, 2USP Technologies, 3Western University, 4Great Lakes Water Authority

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2024

DOI10.2175/193864718825159715

Volume / Issue

Content sourceWEFTEC

Word count14

Are Your Digesters Up to the Task? Aligning Resource Recovery Planning with Reality

Abstract

Abstract Anaerobic digestion serves as the linchpin for much of the wastewater solids treatment in the United States. In many major metropolitan areas, digesters were constructed between the 1950s and 1970s, and are reaching the end of their useful life. As utilities seek to increase resource recovery and intensify digestion, these older vintage digesters may not be able to accommodate simple upgrades that allow for higher temperature or higher total solids operation. Introduction Anerobic digestion sits at the nexus between traditional wastewater treatment and modern utility climate goals, including greenhouse gas (GHG) reduction, landfill diversion, and green energy generation. Utilities performing solids and energy planning around these goals are typically relying heavily upon their anaerobic digesters to be efficient and high performing, often seeking to intensify digestion so as to accommodate imported feedstocks (e.g. fats, oil and grease, food waste, outside sludge, etc.) or simply to provide capacity for future flows and loads within the same tankage. In many major metropolitan areas, digesters were constructed between the 1950s and 1970s, and are reaching the end of their useful life. As utilities seek to increase resource recovery and intensify digestion, these older vintage digesters may not be able to accommodate simple upgrades that allow for higher temperature or higher total solids operation. Results and Discussion When seeking to achieve higher loading rates (either due to increased population in the service area or a desire to import high strength wastes), it is typical for utilities to start the planning process by assessing the potential of existing anaerobic digestion tankage. Intensifying digestion via established processes such as thermophilic digestion or thermal hydrolysis can be an appealing way to expand capacity (see Figure) with a seemingly incremental investment (e.g. heat exchangers, thermal hydrolysis skid). The ability to intensify digestion can be especially important in older cities where sites may be constrained and expansion of a digester complex is not possible. Despite these advantages, however, digestion infrastructure may not be capable of realizing the full potential of intensification due to either structural inadequacy or suboptimal configuration. As a general industry practice, digester tanks are expected to remain in service for 50 to 75 years, with the associated mechanical equipment having a shorter service life of approximately 20 years. Factors that can affect this service life include freeze/thaw cycles, which can weaken concrete, and seismic activity. In addition, many older digesters were constructed with floating covers, and cover integrity, as well as interior and exterior coating integrity, can expose the digester structure to wear inducing conditions. While not a hard trigger, replacement of the digesters prior to reaching 75 years of life serves as a sound rule of thumb. Very few comparable facilities have digester structures of this age operational, although a small number remain in service with plans to replace prior to 2030 (e.g., San Francisco's Southeast Water Pollution Control Plant). In addition, considerations about capacity, given that older digesters were simply not designed to perform at the higher loading rates needed for codigestion applications, amplify the need for eventual replacement of these structures. Other unknowns, including structural vulnerabilities, could accelerate this replacement timeline. Operating conditions associated with higher rate digestion that can be problematic for older digestion infrastructure include higher gas production rates, biogas entrainment, and changes to viscosity. Older gas mixing systems, for example, are likely inadequate for realizing the full active volume of a digester generally, a condition that is exacerbated by sludges of higher total solids content. Changes to viscosity associated with higher total solids content (thicker sludge) and/or inclusion of food waste can, in addition to impacting mixing performance, can entrain biogas, contributing to acute operational issues such as digester foaming. Changes to sludge rheology will also impact ancillary systems, such as pumps and heat exchangers, which should be assessed for upgrades. Higher digester loading limits could potentially be realized if existing digesters are upgraded with features such as improved mixing and surface withdrawal, both of which will help realize the full active volume of the digester and minimize gas and foam entrainment (see Figure). Such upgrades can be included in existing digesters, assuming the structural integrity of the tank is intact. A detailed condition and structural assessment is recommended prior to implementing digester enhancements intended to accommodate higher rate digestion. Conclusions When assessing the capability of existing digesters to process higher organic loads, a thorough assessment must be undertaken. This includes a robust condition assessment, as well as an evaluation of retrofits that can maximize the benefits of intensification. Full costs of such upgrades should be compared against the cost and feasibility of construction of new, modern digesters to help utilities realize their full plans for resource recovery.

This paper was presented at the WEF Residuals & Biosolids and Innovations in Treatment Technology Joint Conference, May 6-9, 2025.

SpeakerSierra, Natalie

Presentation time

10:45:00

11:05:00

Session time

10:45:00

11:45:00

SessionPractical Considerations in Digestion

Session number4

Session locationBaltimore Convention Center, Baltimore, Maryland, USA

TopicAnaerobic co-digestion, Biomethane, Lipids/proteins/carbohydrates ratio, TWAS, Manure, SSO, Anaerobic Digestion, Asset Management, Biomethane Potential Test, Condition Assessment, Corrosion, Intensification, Resource Recovery, Struvite

Author(s)

Sierra, Natalie, Muller, Christopher

Author(s)N. Sierra1, C. Muller1

Author affiliation(s)Brown and Caldwell, 1Brown and Caldwell, 1

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date May 2025

DOI10.2175/193864718825159777

Volume / Issue

Content sourceResiduals and Biosolids Conference

Word count14

Description: Arrested Anaerobic Digestion and Recovery of Value-added Products Through...

Arrested Anaerobic Digestion and Recovery of Value-added Products Through Vacuum-intensified Alkaline Fermentation

Abstract

In this proof of concept experimental work, it was demonstrated that vacuum-driven fermentation can enable efficient resource recovery from municipal sludge and provide means to arrest anaerobic treatment to maximize extraction of added value products such as ammonia and volatile fatty acids (VFA). The concept relies on applying low vacuum to strip ammonium from fermented sludge, allowing the recovery of ammonium sulfate by chemisorption. Moreover, volatile fatty acids and soluble phosphorus, highly concentrated in the fermentate, can be separated using a pre-conditioning step based on iron flocculation and hydrogen peroxide (to precipitate phosphates) followed by mechanical filtration. This way, nutrient-free soluble carbon and volatile fatty acids can be recovered in the filtrate, while nutrient-rich solids can be further processed by anaerobic digestion or directly used as soil amendment and fertilizers. In this project, a feasibility study, centered on laboratory tests and model-based analysis, to determine the viability of this new process to accelerate the realization of circular economy in the wastewater industry. The study was designed to confirm the impact of pH on the ability to improve VFA production from fermentation and improve the selective separation of ammonia through stripping compared to conventional fermentation or vacuum assisted fermentation without pH adjustment. It also confirmed whether the value-added products recovered by vacuum technologies can maintain high yields and sufficient purity for circular applications (i.e., supplemental carbon for biological nutrient removal, fertilizers for agriculture, carbon-based precursors to bioplastics, etc.). The study demonstrated the improvement of ammonia recovery by more than double compared to vacuum at neutral pH. In addition, VFA yield was improved by 84% compared to the control. Operating in alkaline conditions ceased the methanogenesis process resulting in accumulation of VFA. On the other hand, the elevated pH reduced the undissociated acids concentrations, which may have resulted in improved hydrolysis and fermentation rates.

SpeakerAl-Omari, Ahmed

Presentation time

14:00:00

14:20:00

Session time

13:30:00

15:00:00

SessionAdvances in Anaerobic Digestion and Sidestream Treatment

Session locationRoom S404a - Level 4

TopicIntermediate Level

Author(s)

Al-Omari, Ahmed

Author(s)A. Al-Omari 1; Kirim 2 ; X. Bai 3; J. J. Walton 4; C. Muller 5; K. Bell 6; D. Santoro 7; G. Nakhla 8; A. Al-Omari 1;

Author affiliation(s)Brown and Caldwell 1; 5; 6; 7; 8;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2023

DOI10.2175/193864718825158984

Volume / Issue

Content sourceWEFTEC

Word count13

Description: Bench Scale Comparison of Vacuum Evaporation Enhanced Anaerobic Digestion...

Bench Scale Comparison of Vacuum Evaporation Enhanced Anaerobic Digestion (IntensiCarbTM) with Thermal Hydrolysis

Abstract

Thermal hydrolysis represents the state-of-the-art intensification for anaerobic sludge stabilization currently, providing high loading capacity, pathogen kill to Class A standard, reduced sludge viscosity and improved sludge dewaterability. Emerging intensification processes need to provide a similar or better range of benefits to drawbacks or provide similar levels at a lower lifecycle cost to enter the market effectively. The first step in this process is to understand the relative process performance of the two systems, treating sludges from the same facility.

A bench-scale pilot study was conducted at Western University to explore how the IntensiCarb™ process compares to thermal hydrolysis operated at their typical loading rates (Figure 1). For the IntensiCarb™ process this involved operating at a 20-day SRT and 5-day HRT and for thermal hydrolysis this represents operating at an SRT of 20 days, a maximum organic loading rate of <0.400 lb-VS/ft3-d and total ammonium-N concentration of < 3,000 mg-N/L. Thermal hydrolysis was conducted at 150°C for 30 minutes, prior to feeding to the digesters. The feed sludge to digestion was a mix of primary and secondary sludge from the Greenway Wastewater Treatment Plant, as characterized in Table 1.

Under the operating conditions outlined, above a variety of process metrics were evaluated to determine process performance and any relative differences between the two processes. Figure 2 compares the methane yield of the digesters (L-CH4/gCODfed) between the IC reactor and the THP system. What is apparent in the data is that during early operation the yield was comparable, but after approximately 1.75 SRTs there was a marked drop off in the methane production from the THP system, decreasing to 0.07 L-CH4/g-CODfed as compared to the IC system at 0.22 L-CH4/g-CODfed. As subsequently discussed, the drop in production was likely due to ammonia-N toxicity.

Figure 3, shows total ammonia-N concentration in the digesters. The IC digester operated between 800-1200 mg-N/L over the course of the evaluation period. The THP digester total ammonia-N increased to an average of 3,200 mg-N/L, above typical process limits. The THP digester was allowed to run for an additional 2 SRTs beyond the first indication of process deterioration. This was done to understand if the biomass, given sufficient time would acclimate to the ammonia. However, no improvement was realized. Specific methanogenic activity tests were conducted during this time to confirm that it was ammonia toxicity impacting the methanogenic population. SMA testing demonstrated consistent methane production from the IC digesters, while the THP sludge produced no gas, indicating acetoclastic methanogenesis was completely inhibited by ammonia. While the loading rate of the IC digester was high, it was protected by the removal of ammonia during the evaporation process. Figure 4 shows the partitioning of total ammonia-N between the digester and that removed in the condensate. Approximately 57% of the organic nitrogen converted to ammonium was removed in the condensate, keeping the concentration in the digester at tolerable levels.

Volatile acid data supported the observation that methanogenic activity was primarily inhibited by the elevated ammonia-N levels in the THP digester, as total VFA rose to concentrations greater the 8,000 mg/L as acetate (Figure 5). The data also appears to support prior observations regarding IC operations, that overtime there is a shift in the microbial community, as biogas production stabilized but VFA levels continued to decrease after 2.5 SRTs. Had the system fully stabilized, system performance should have been similar to prior SRTs of operation. The data to date indicate that for these high load systems, acclimation is critical to long-term performance. After several attempts at trying to recover the THP digestion system from ammonia toxicity it was decided the best course of action would be to reseed the digester with sludge from an operating thermal hydrolysis unit. Sludge was shipped overnight from the DCWater Blue Plains Advanced Wastewater Treatment Plant in Washington, DC which has been operating a CAMBI thermal hydrolysis process since 2014. By inoculating the THP digestion system with biomass acclimated to high load and high ammonia levels, a more representative comparative analysis could be conducted.

After approximately 20 days of operation the inoculated THP digester has shown strong performance and not exhibited the high VFA and low methane production its predecessor had, while being fed the same sludge from the Greenway facility. The results suggest that acclimation of biomass is increasingly critical for some digestion processes as loading rates increase beyond conventional norms.

This paper will present the complete data from both IC and THP trials, including the reseed reactor performance and ammonia stress trials investigating process robustness (data not shown). The final paper will present a direct comparison of process performance and an evaluation of the different impacts the two intensification strategies have on anaerobic digestion. This paper will provides a direct comparison of the current state-of-the-art digestion operations with a new and emerging technology demonstrating how different intensification strategies can address specific user needs and critical success factors.

This paper was presented at WEFTEC 2025, held September 27-October 1, 2025 in Chicago, Illinois.

Presentation time

16:30:00

17:00:00

Session time

15:30:00

17:00:00

SessionChallenges and Innovation in Sludge Processing

Session locationMcCormick Place, Chicago, Illinois, USA

TopicResearch

Author(s)

Muller, Christopher, Khadir, Ali, Al-Omari, Ahmed, Santoro, Domenico, Sheculski, Chris, Bell, Katherine, Parker, Wayne, Nakhla, George

Author(s)C. Muller1, A. Khadir2, A. Al-Omari1, D. Santoro3, C. Sheculski3, K. Bell1, W. Parker4, G. Nakhla2

Author affiliation(s)Brown and Caldwell1, Western Univerisity2, Trojan Technologies3, Univerisity of Waterloo4

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Sep 2025

DOI10.2175/193864718825160151

Volume / Issue

Content sourceWEFTEC

Word count14

Description: Building A New Digester or Intensifying the Existing Anaerobic Digesters? A Deep...

Building A New Digester or Intensifying the Existing Anaerobic Digesters? A Deep Dive into Advanced AD Intensification Technologies in North America

Abstract

Introduction and Objectives
Anaerobic digestion (AD) has been widely adopted by municipalities for solids management in wastewater resource recovery facilities (WRRF). AD enhances resource recovery, adding value to wastewater treatment. However, its kinetics pose challenges, with slow hydrolysis and methanogenesis necessitating a solid residence time (SRT) of 15-20 days, leading to larger footprints and higher construction costs. Faster growing acidogenic microorganisms produce inhibitory substances that destabilize the process, especially when organic loading rates increase or feed material resists hydrolysis. Furthermore, population growth demands a capacity increase in AD tanks to handle the higher wastewater sludge flowing into the plants. A traditional method to increase the capacity of the digesters for a utility is building new digesters which requires relatively high capital and operation costs. Tackling such challenges necessitates adopting advanced AD intensification technologies that alleviate the biological limitations, provide smaller footprint, and increase capacity at lower costs.

Intensification technologies are a general umbrella term to include any technology that improves the performance of AD systems. The benefits of intensification technologies include, but are not limited to, enhanced production of valuable products, reduced process footprints, higher organic loading, and improved process stability. In practice, municipalities make ad hoc decisions to select intensification technologies available commercially that meet their regulatory and financial needs. To the best of our knowledge, there are no comprehensive analyses and references available in our industry that cover the practitioners to select appropriate intensification technology for their municipalities and compare the existing advanced AD technologies in North America.

The objective of this study is to discuss and analyze the benefits of intensification technologies for AD in WRRF. The goal is to provide the municipalities with a comprehensive framework to select and implement appropriate intensification technologies, considering their specific needs and conditions, to enhance the performance and efficiency of AD processes.

Methodology
Six municipalities in North America were interviewed that each have implemented one of the full-scale intensification technologies, and further compared and analyzed the benefits of intensification technologies. First, a literature survey was conducted to identify and compare currently used intensification technologies by municipalities in North America. Six major intensification technologies were identified including Acid-Phase Digestion (APD), Temperature-Phased Digestion (TPAD), Recuperative Thickening (RT), Thermal Hydrolysis (THP), Post-Aerobic Digestion (PAD), and High Solid Digestion. Then, for each intensification technology, an offline survey and an hour-long interview were conducted with a municipality that has adopted the technology to understand their experience. Finally, a framework for evaluating the advantages and disadvantages of each intensification technology was developed.

Results
Figures 1 and 2 show approximately sixty plants in North America have adopted advanced AD technologies with TPAD, THP, and APD being the top 3 technologies implemented today. While for RT, high solid digestion, and PAD only one facility for each has adopted the technology to date. The interviews of municipalities sought many common features of intensification technologies. These attributes included higher organic loading rate, decoupling SRT from HRT, improved process stability, ease of operation, and enhanced recovery of valued products reported in Table 1. Interestingly, while seeking similar attributes from an intensification technology, the choice of intensification technology rarely depended on the technological advantages alone. Rather, each municipality's choice of intensification technology reflected their unique concerns reflecting the history of their facility, relationship with their local constituents, influent characteristics, and other economic opportunities. For example, Madison Metropolitan Sewerage District (MMSD) adopted a two-phase AD process to retrofit an existing AD facility to cope with persistent foaming issues they had been dealing with historically. The City of Montpelier Water Resource Recovery Facility constructed a new AD with a recuperative thickener (RT) to be able to maintain high SRT in response to incidental high organic loading events. DC Water adopted Thermal Hydrolysis to increase capacity.

In conclusion, intensification technologies significantly enhance anaerobic digestion (AD) performance by boosting stability, increasing organic loading rates, and reducing costs and footprints. This study provides a detailed framework for municipalities to choose the best technology tailored to their unique needs, emphasizing the importance of a customized approach over a one-size-fits-all solution.

This paper was presented at WEFTEC 2025, held September 27-October 1, 2025 in Chicago, Illinois.

Presentation time

09:00:00

09:30:00

Session time

08:30:00

10:00:00

SessionPass the Gas: Digester Rehab, Intensification, and Innovation

Session locationMcCormick Place, Chicago, Illinois, USA

TopicBiosolids & Residuals

Author(s)

Kakar, Farokh Laqa, Elsayed, Ahmed, Marcus, Andrew, Zareie, Mahdis, Norton, John, Jankowski, Kevin, Cox, Christopher, Seib, Matt, Peot, Chris, Morse, Thomas, Smillova, Diana, Muller, Christopher, Elbeshbishy, Elsayed

Author(s)F. Kakar1, A. Elsayed2, A. Marcus3, M. Zareie2, J. Norton3, K. Jankowski3, C. Cox4, M. Seib5, C. Peot6, T. Morse7, D. Smillova8, C. Muller1, E. Elbeshbishy2

Author affiliation(s)Brown and Caldwell1, Toronto Metropolitan University2, Great Lakes Water Authority (GLWA)3, City of Montpelier WRRF4, Madison Metropolitan Sewerage District5, DC Water & Sewer Authority6, Metro Water Recovery7, City of St. Petersburg8

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Sep 2025

DOI10.2175/193864718825160170

Volume / Issue

Content sourceWEFTEC

Word count22

Description: Comparing Modeling Tools Visual MINTEQ and OLI Studio to Evaluate Scaling Tendency...

Comparing Modeling Tools Visual MINTEQ and OLI Studio to Evaluate Scaling Tendency of Aerated Anaerobically Digested Solids: A Pilot Study

Abstract

Purpose: Common phosphate minerals in wastewater treatment plants, such as struvite/magnesium ammonium phosphate (MAP, MgNH4PO4- 6H2O), calcium phosphates such as amorphous calcium phosphate (ACP, Ca3(PO4)2), and iron salt precipitates such as vivianite (Fe3(PO4)2 8H2O), are known for their tendency to scale and deposit within anaerobic digesters, pipe bends, and dewatering equipment downstream of anaerobic digesters. These deposits pose maintenance and operational challenges. Precipitation of these minerals occurs when the concentrations of ionic constituents exceed the solubility product (Ksp) of the solid, measured as scaling tendency (ST) or saturation index (SI). The solubility of these precipitates depends on factors such as pH, temperature, competing ions, and nucleation sites. Chemical thermodynamic modeling can evaluate the parameters contributing to scaling and, thereby, safeguard process equipment from scaling-induced damage, improve treatment efficiency, and regulate phosphorus sequestration to produce nutrient-rich biosolids. This modeling work could benefit the wastewater treatment industry by providing rapid optioneering for solutions limiting and targeting scaling mineral deposition and assessing various process optimizations for new pilot technologies. In this study, two chemical thermodynamic models were evaluated: (i) Visual MINTEQ Version 4.0 and (ii) OLI Studio. Model inputs were gathered from a pilot-scale experimental setup at Hampton Roads Sanitation District's (HRSD) Atlantic Treatment Plant (ATP), in Virginia Beach, VA. The pilot evaluated the impact of aeration, mixing, and chemical addition on the scaling tendency of thermally hydrolyzed, pretreated, anaerobically digested solids. Critical parameters such as pH, temperature, alkalinity, orthophosphate (OP), ammonia (NH3), and major cations and anions concentrations were measured as model inputs. The solids formed during these evaluations were characterized by: X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM)/Energy Dispersive X-Ray Spectroscopy (EDS), and Raman Spectroscopy analysis to validate predictions of the two models. Methods: The pilot setup at ATP consisted of four tanks (Figure 1), each 11 feet tall and capable of holding about 45 gallons of digestate. These tanks operated as daily batch fed continuously stirred tank reactors, maintained by pump recirculation at a 3-day solids retention time (SRT). Aeration was provided using fine bubble diffuser membranes, operated either at a constant airflow rate or via a dissolved oxygen (DO) set point. The effects of chemical injection of magnesium hydroxide [Mg(OH)2] and calcium hydroxide [Ca(OH)2] were also studied at various Ca+Mg:OP ratios of 0 (control), 0.25:1, 0.5:1, and 1:1. The modeling process was based on pilot operational conditions: anaerobic digestate (pilot influent), aerated anaerobic digestate constantly at 5 LPM, and aerated anaerobic digestate on a DO setpoint of 0.2 mg/L. Inputs for these operational conditions were collected during pilot tests and averaged for model insertion. For each model run, pH and temperature sensitivity analyses were conducted from pH 7-9, and temperatures 20 - 40°C to determine effects on precipitate formation according to Visual MINTEQ and OLI Studio. Experiments with Mg(OH)2 and Ca(OH)2 were conducted in both models for the aerated cases to simulate chemical injection and evaluate the effectiveness of each chemical in OP removal, as well as the accuracy of each model in predicting mineral formation. Results: Both Visual MINTEQ and OLI Studio effectively predicted mineral formation in anaerobic digestate under varying conditions. Initially, both models predicted the formation of metal phosphates (Mg, Ca, Fe) in anaerobic digestate. Upon aeration at 5 LPM, both models identified struvite as the dominant mineral formed in the pH sensitivity analysis, though they differed in predicting other compounds. Visual MINTEQ predicted the formation of calcite and vivianite, while OLI Studio predicted tricalcium phosphates, calcite, and siderite. In the temperature sensitivity analysis, both models yielded consistent results for calcite and struvite formation, suggesting that temperature has a less significant impact on mineral precipitation than pH. In the aerated run targeting a DO setpoint of 0.2 mg/L with Mg(OH)2, both models accurately predicted struvite as the dominant mineral, with its formation increasing alongside the chemical dose, as depicted in Figures 2 and 3. Table 1 compares the OP removal predicted by each model to the measured pilot results for the same test. Both models closely aligned with the measured OP removal via struvite formation, and solid-phase characterization confirmed struvite as the major compound, as indicated by XRD pattern peaks. The presentation will showcase the outcomes derived from each model, offering insights into their respective abilities to predict the potential for the precipitation of controlling solids. The precipitate characterization analysis will also be compared to determine the validity of results and to further optimize both modeling software. The results of this study will enhance our understanding regarding scaling minerals likely to form within anaerobic digestion pretreated with a thermal hydrolysis process, post anaerobic digestion, and on downstream equipment, as well as in a potential post aerobic digestion setup. A validated model could then be used to predict scaling potential and characterize minerals formed at other WRRFs to better treat these nuisance scaling minerals and determine their potential for harvesting/sequestration as a nutrient rich product.

This paper was presented at the WEF Residuals & Biosolids and Innovations in Treatment Technology Joint Conference, May 6-9, 2025.

SpeakerHarris, Caitlyn

Presentation time

15:45:00

16:05:00

Session time

15:45:00

16:45:00

SessionAdvances in Process Modeling: Aeration, Scaling, and Anaerobic Digestion Dynamics

Session number20

Session locationBaltimore Convention Center, Baltimore, Maryland, USA

TopicChemical Treatment, Modeling, Phosphorus Removal and Recovery, Specific Methanogenic Activity Test

Author(s)

Harris, Caitlyn, Oza, Shubhashini, Nicholson, Jeffrey, Ward, BJ, Matel, Holly Anne, Bott, Charles, Muller, Christopher, Wilson, Christopher

Author(s)C. Harris1, S. Oza1, J. Nicholson2, B. Ward2, H. Matel2, C. Bott2, C. Muller1, C. Wilson2

Author affiliation(s)Brown and Caldwell, 1Brown and Caldwell, 1Hampton Roads Sanitation District (HRSD), 2Hampton Roads Sanitation Department, 2Hampton Roads Sanitation District (HRSD), 2Hampton Roads Sanitation District (HRSD), 2Brown and Caldwell, 1

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date May 2025

DOI10.2175/193864718825159765

Volume / Issue

Content sourceResiduals and Biosolids Conference

Word count21

Comparing Modeling Tools Visual MINTEQ and OLI Studio to Evaluate Scaling Tendency of Aerated Anaerobically Digested Solids: A Pilot Study

Abstract

Common phosphate minerals in wastewater treatment plants such as struvite (MAP, MgNH4PO4*6H2O), calcium phosphates such as amorphous calcium phosphate (ACP, Ca3(PO4)2), and iron salt precipitates such as vivianite (Fe3(PO4)2*8H2O) have been recognized as a maintenance and operational nuisance for their tendency to scale and deposit within anaerobic digesters, in pipe bends, and on dewatering equipment downstream of anaerobic digesters. Precipitation of these minerals occur if the concentrations of the ionic constituents exceed the solubility product (Ksp) of the solid which is measured as scaling tendency (ST) or scaling index (SI). The solubility of these precipitates is dependent on factors such as pH, temperature, other competing ions, and nucleation sites. Chemical thermodynamic modeling could be used in evaluating the parameters that contribute to scaling and, thereby, safeguard process equipment from scaling-induced damage, improve treatment efficiency, and regulate phosphorus sequestration to produce nutrient rich biosolids. In this study two commercially available models were evaluated: (i) Visual MINTEQ Version 4.0 and (ii) OLI Studio. The model inputs were gathered at a pilot-scale experimental setup at Hampton Roads Sanitation District's (HRSD) Atlantic Treatment Plant (ATP), Virginia Beach, VA. The pilot evaluates the impact of aeration, mixing, and chemical addition of thermally hydrolyzed pretreated, anaerobically digested solids on scaling tendency. Critical parameters such as pH, temperature, alkalinity, orthophosphate (OP), ammonia (NH3), and major cations and anions concentrations were measured as model inputs. The solids formed during these evaluations were characterized by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM)/Energy Dispersive X-Ray Spectroscopy (EDS), and Raman Spectroscopy analysis to validate prediction by the two models. The pilot set up at ATP consists of four tanks (Figure 1). Each tank is 11 feet tall and can hold up to about 63 gallons of digestate. The tanks are operated as daily batch fed continuously stirred tank reactors maintained by pump recirculation at a 3-day solids retention time (SRT). The tanks are aerated with fine bubble diffuser membranes which can be operated at constant or intermittent air flow rates, via dissolved oxygen (DO) or pH set points. Chemical injection lines will be added to measure the effects of calcium hydroxide [Ca(OH)2] and magnesium hydroxide [Mg(OH)2] at varying dosages. The modelling process was based on the pilot influent solution compositions depicted in Table 1 of anaerobic digestate. In both modeling programs, anaerobically digested solids at a temperature of 30 degrees C, a pH of 7.4, and initial parameters from Table 1 were analyzed to determine the pilot influent potential precipitate formation. Figure 2 represents the fractions of solids predicted to form at equilibrium in Visual MINTEQ and Figure 3 displays similar results produced from OLI, both in mg/L. The two model predictions are closely related, listing siderite, struvite, and calcite as the top three controlling precipitates, respectively. This is a prediction of what is forming currently in the digesters, prior to manipulation in the pilot from aeration or chemical addition. A pH sweep from 7 to 8.5 as well as a temperature sweep from 20 degrees C to 40 degrees C were also analyzed in both modeling programs to understand the effects of aeration within the pilot on pH, biological activity, and how the solubility of scaling precipitates were affected. These results, as well as future work that includes modeling the effects of chemical addition in the pilot, will be presented. Precipitate Characterization was conducted in a contract laboratory for XRD, SEM/EDS, and Raman Spectroscopy to determine precipitate identification. The major peaks in XRD patterns produced likely matched with struvite. Further testing will be completed and presented to validate the solids predicted to form by the models. The presentation will showcase the outcomes derived from each model, offering insights into their respective abilities to predict the potential precipitation of controlling solids. The precipitate characterization analysis will also be compared to determine the validity of results and to further optimize both modeling software.

Two models were evaluated: (i) Visual MINTEQ and (ii) OLI Studio. A pilot study assessed the impact of aeration and mixing of thermally hydrolyzed pretreated, anaerobically digested solids on scaling tendency and measured pH, temperature, orthophosphate, ammonia, and major cations and anions concentrations as model inputs. Sensitivity analyses for pH and temperature were conducted for both unaerated and aerated anaerobic digestate in each model.

SpeakerHarris, Caitlyn

Presentation time

13:30:00

14:00:00

Session time

13:30:00

15:00:00

SessionInnovations in Phosphorus Management: From Models to Solutions

Session number603

Session locationRoom 340

TopicFacility Operations and Maintenance, Intermediate Level, Municipal Wastewater Treatment Design, Nutrients, Research and Innovation

Author(s)

Harris, Caitlyn, Oza, Shubhashini, Nicholson, Jeffrey, Matel, Holly Anne, Ward, Barbara, Bell, Katherine, Muller, Christopher, Wilson, Christopher, Bott, Charles

Author(s)C.A. Harris1, S. Oza2, J.D. Nicholson3, H. Matel3, B.J. Ward3, K.Y. Bell4, C. Muller5, C. Wilson1, C.B. Bott3

Author affiliation(s)1HRSD, VA, 2Brown and Caldwell, NC, 3Hampton Roads Sanitation District (HRSD), VA, 4Brown and Caldwell, CA, 5Brown and Caldwell, MA

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2024

DOI10.2175/193864718825159528

Volume / Issue

Content sourceWEFTEC

Word count21

Description: Fermentation Intensification with Vacuum-Assisted Technology: An Evaluation of...

Fermentation Intensification with Vacuum-Assisted Technology: An Evaluation of Full-Scale EBPR Alternatives Using a Calibrated Process Model Analysis

Abstract

IntensiCarb® is a vacuum-based intensification technology that provides process benefits in fermentation or anaerobic digestion. Applying this technology to fermentation allows for half the process volume to achieve improved yield of volatile fatty acids (VFA) for beneficial use. Generating VFA from fermentation provides a benefit to facilities that need supplemental carbon for nutrient removal targets in the liquid treatment process. VFA can be used by facilities to improve enhanced biological phosphorus removal (EBPR) performance, lowering effluent total phosphorus (TP) concentrations. An analysis was completed to evaluate the process performance and life-cycle costs of IntensiCarb® relative to chemical addition and conventional fermentation alternatives for TP removal. Experimental results on vacuum-assisted process intensification were used in the process performance analysis and GHG emissions were estimated to compare alternatives. The evaluation suggests IntensiCarb® is competitive with other alternatives to lower effluent TP with EBPR. FeCl3 chemical addition had the lowest life-cycle cost overall

IntensiCarbÂ® is a vacuum-based intensification technology that provides process benefits in fermentation or anaerobic digestion. An analysis was completed to evaluate the performance and life-cycle costs of IntensiCarbÂ® relative to chemical addition and conventional fermentation alternatives for the purposes of phosphorus removal. This paper describes bench-scale experimental results, presents model performance predictions, and compares life-cycle costs and greenhouse gas emission estimates.

SpeakerArmenta, Maxwell

Presentation time

16:10:00

16:30:00

Session time

15:30:00

17:00:00

SessionExtracting Carbon for Nutrient Removal

Session locationRoom S403a - Level 4

TopicFacility Operations and Maintenance, Intermediate Level, Municipal Wastewater Treatment Design, Nutrients

Author(s)

Armenta, Maxwell

Author(s)M. Armenta 1; F. Kakar 2 ; A. Al-Omari 3; C. Muller 4; K. Bell 5; G. Nakhla 6; D. Santoro 7; J. Boone 7; M. Armenta 1; R. Coleman 8;

Author affiliation(s)Brown and Caldwell 1; Brown and Caldwell 2 ; Brown and Caldwell 3; Brown and Caldwell 4; Brown and Caldwell 5; University of Western Ontario, London, ON 6; USP Technologies 7; PRAB, Kalamazoo, MI 7; Brown and Caldwell 1; Environmental Operating Solutions, Inc. 8;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2023

DOI10.2175/193864718825159027

Volume / Issue

Content sourceWEFTEC

Word count18

Description: Full-scale demonstration of micro-aeration for hydrogen sulfide control at the...

Full-scale demonstration of micro-aeration for hydrogen sulfide control at the Chambers Creek Regional Wastewater Treatment Plant

Abstract

Wastewater utilities are increasingly engaged in projects that beneficially utilize biogas in renewable energy applications. Although the degree to which the biogas must be cleaned or upgraded will depend on its end use, the removal of hydrogen sulfide (H2S) to varying degrees will always be required. Historically, hydrogen sulfide has been treated using chemical scrubbers or adsorptive processes, but these tend to be costly and maintenance intensive. The addition of small amounts of oxygen, whether by air or high purity oxygen systems, to anaerobic digesters has been reported to be an effective and economical mitigation measure for hydrogen sulfide. The Pierce County Department of Public Works and Utilities (County) uses digester gas at their Chambers Creek Wastewater Regional Wastewater Treatment Plant to power boilers which were installed in 2016. Although the boilers are relatively new, the County has had to replace fouled boiler tubes approximately every six months of operation due to the levels of hydrogen sulfide in the biogas (2200 ppm, on average). (Figure 1) Consequently, the County requested that Brown and Caldwell (BC) evaluate different technologies to reduce hydrogen sulfide concentrations to levels closer to boiler manufacturer recommendations (10 parts per million by volume [ppmv]), which would in turn reduce maintenance and costly tube replacement. Although the use of sacrificial media is a feasible alternative and one that the County may implement in coming years, the level of treatment required for the current biogas hydrogen sulfide concentrations would require frequent and costly media replacement. BC recommended that the County pilot microaeration, which would not reduce H2S concentrations to the levels required but rather extend the life of any adsorptive/sacrificial media and reduce associated operating costs. The pilot design was informed by a literature review conducted prior to implementation in order to ascertain appropriate design and control parameters and to review the particular importance of biogas residence time in gaseous hydrogen sulfide removal efficiency and air requirements for effective sulfide reduction. Residence times of approximately five hours showed a relatively consistent removal of 90%; the results of the literature review on air quantity required was mixed. Various sources indicated that, in pilot systems, approximately two to three times the theoretical air requirement was needed to affect the anticipated hydrogen sulfide reduction, while in full scale systems, about four times the theoretical air requirements are needed, potentially due to mixing and oxygen transfer as well as different surface area-to-volume ratios. A linear relationship between mass of air supplied and mass of H2S removed was reported to be approximately 2.05 kg O2/kg H2S removed, which is again four times the theoretical value based on oxidation to sulfur. Finally, oxygen concentrations in the digesters subjected to microaeration were found to be on the order of 1-2% The Chambers Creek microaeration pilot was designed in two phases. Data on two digesters receiving the same feed loads (total and volatile solids) were collected as part of phase one, prior to the beginning of aeration, in order to baseline existing conditions and variations in digester operation (see Table 1). Data were collected for approximately five months between August and December of 2021. Phase two began in January of 2022; one digester was chose as the treatment digester, and one as the control. 90 scfh of plant air was introduced into the sludge feed line upstream of the treated digester through an air injection assembly, with data continuing to be collected on both digesters for comparison. The initial aeration dose was chosen based on the County's desire to maintain the minimum reported oxygen level of 0.2% in the digester so as to minimize disruption to the digestion process. At biogas sulfide loads of approximately 16kg/day, the air flow rate of 90scfh corresponds to a ratio of 1.03 kg O2/kg H2S and a molar ratio of 1.09 mol O2/mol H2S. At these ratios, approximately 12% removal in hydrogen sulfide (mass basis) in the aerated digester was realized after three weeks of operation. Both the mass and molar ratios are generally lower than those identified in the literature review, data that, when coupled with the significantly lower biogas residence time, indicate that lower aeration rates may still positively impact sulfide removal. The full-scale demonstration of micro-aeration at Pierce County, resulted in an approximate 15% reduction in the biogas hydrogen sulfide levels; a reduction less that that reported possible in the literature. An evaluation of the data, digester microbial population data and digester gas system inspection provided valuable lessons learned surrounding the implementation of microaeration at scale. These include: - The addition of small quantities of oxygen do not negatively impact the anaerobic community. - Surface area is critical for microaeration to successfully remove H2S - Digester gas management systems in systems with microaeration should be designed such that biofilm and sulfur management are possible (Figure 2) - Microbial community analysis indicates that primary H2S metabolism is likely to be in the biofilm and not the bulk digestion phase. - Online monitoring is critical to process success and control, with feedback control (Figure 3) - Digestion processes that have relatively small headspaces (ex. egg-shaped digesters, submerged fixed covers) may want to consider ex-situ treatment of H2S. This paper will discuss the results of this pilot as well as the lessons learned and how they may be applied to future installations to mitigate the challenges of this emerging process.

This paper was presented at the WEF Residuals and Biosolids Conference, June 18-21, 2024.

SpeakerMuller, Christopher

Presentation time

10:45:00

11:15:00

Session time

08:30:00

11:15:00

SessionEnergy Management: From Production to Safety

Session number25

Session locationOklahoma City Convention Center, Oklahoma City, Oklahoma

TopicBiogas Cleaning, Biogas desulfurization, Microaeration

Author(s)

Muller, Christopher

Author(s)C. Muller1, K. Guevarra2, A. Summers2, P. Zemke1, K. Woodland1, V. Hollingsworth1, E. Bronstad1

Author affiliation(s)Brown and Caldwell 1; Pierce County Public Works and Utilities 2; Pierce County Public Works and Utilities 2; Brown and Caldwell 1; Brown and Caldwell 1; Brown and Caldwell 1; Brown and Caldwell 1;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Jun 2024

DOI10.2175/193864718825159476

Volume / Issue

Content sourceResiduals and Biosolids Conference

Word count17

Description: Innovation Portfolio Management for Retrofitting Advanced Biotechnologies for...

Innovation Portfolio Management for Retrofitting Advanced Biotechnologies for Anaerobic Digestion Process at Lulu Island Wastewater Treatment Plant

Abstract

Metro Vancouver recently commissioned the Pilot Digestion Optimization Facility (PDOF) at its Lulu Island Wastewater Treatment Plant (LI WWTP) to facilitate the evaluation of different digestion optimization technologies without risk to full-scale plant operation. This study summarizes the integrated approach adopted at the pilot-scale preliminary design stage for two of these technologies. The first technology aims to increase biogas production rates by testing the Direct Interspecies Electron Transfer (DIET) process using electroconductive materials. The second technology utilizes a biological hydrogen methanation (BHM) process to convert the carbon dioxide portion of biogas into renewable natural gas (RNG) using hydrogen. Cost-effective pilot-scale conceptual designs are developed for testing the in-situ and ex-situ configurations of these technologies in order to reach a go/no-go decision quickly, while still producing replicable results for further scale-up. To guide the decision-making process for selecting these technologies for pilot testing, GHG emission reduction calculations and an energy balance model are used to evaluate the environmental impacts of implementing these technologies at full-scale. A Sumo model is used to evaluate the effects of implementing these technologies on process intensification.

Metro Vancouver, in collaboration with its partners, is developing innovative technologies that reduce greenhouse gas emissions and intensify existing digestion processes. Metro Vancouver will first assess the effectiveness and scalability of these technologies at the Lulu Island Pilot Digestion Optimization Facility. Metro Vancouver intends to incorporate these technologies into one of its treatment facilities if the technologies prove successful at pilot-scale.

SpeakerChegounian, Parisa

Presentation time

15:30:00

15:50:00

Session time

15:30:00

17:00:00

SessionImproving Biosolids Treatment Efficiency

Session locationRoom S403b - Level 4

TopicEnergy Production, Conservation, and Management, Intermediate Level, Research and Innovation

Author(s)

Kakar, Farokh Laqa

Author(s)F. Kakar 1; C. Muller 2 ; T. Barber 3; F. Kakar 1; P. Chegounian 4; L. Zaremba 4; T. Gregonia 4; P. Kadota 4; S. Sorensen 4; A. Al-Omari 5;

Author affiliation(s)Brown and Caldwell 1; Brown and Caldwell 2 ; Brown and Caldwell 3; Brown and Caldwell 1; Liquid Waste Services Department, Metro Vancouver, Burnaby, BC, Canada 4; Liquid Waste Services Department, Metro Vancouver, Burnaby, BC, Canada 4; Liquid Waste Services Department, Metro Vancouver, Burnaby, BC, Canada 4; Liquid Waste Services Department, Metro Vancouver, Burnaby, BC, Canada 4; Liquid Waste Services Department 4; Brown and Caldwell 5;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2023

DOI10.2175/193864718825159034

Volume / Issue

Content sourceWEFTEC

Word count18

Description: IntensiCarbTM- A Novel Vacuum Evaporative Process for the Intensification of...

IntensiCarbTM- A Novel Vacuum Evaporative Process for the Intensification of Anaerobic Digestion

Abstract

Mesophilic anaerobic digestion is the most deployed biological sludge stabilization process at wastewater treatment plants in North America. It also plays a central role in energy and resource recovery from wastewater treatment plants. This paper explores the application of medium vacuum pressure (~100 mbar) operated in a side stream recirculating reactor as a mechanism for process intensification and resource recovery, utilizing the IntensiCarbTM process. Currently within the industry the primary means of process intensification are either through the elevation of operating temperature (ex. thermophilic digestion), pre-conditioning of sludges (ex. thermal hydrolysis) or separation of solids and hydraulic retention time (ex. recuperative thickening). The IntensiCarbTM process utilizes the decoupling of SRT and HRT to increase process capacity while simultaneously reducing the influence of toxic metabolic by products through extraction (ex. ammonia-N). This paper discusses the results of side-by-side comparison of conventional mesophilic digestion with varying intensification factors (2x, 3x, 4x) for bench-scale trials conducted at Western University in London, Ontario, based on the process flow provided in Figure 1. The intent of this experimental design was to focus on understanding the fundamental process changes that occur when vacuum evaporation is applied to a conventional mesophilic digester. In particular, the question being investigated is whether the evaporation process and the extraction of materials result in any fundamental changes in the operation of the digestion process or does it simply operate in a manner similar to recuperative thickening. Table 1 provides a summary of the operating conditions tested, with Intensification Factor 1 (IF1) representing the control and IF2, 3 and 4 representing varying degrees of decoupling of both SRT and HRT. All the digesters were fed a mix of primary and secondary sludge (Ave. TS = 2.9%, VS =2.18%) periodically collected from the Greenway Wastewater Treatment Plant in London, Ontario. The digesters were all operated at mesophilic temperatures (~35-37 °C). Across the range of intensification factors tested, in general, all processes demonstrated effective anaerobic digestion of the sludge, noting that the highest intensification factor (IF-4) there were episodic instability events (data not shown). This suggests that either the process is approaching its maximum extent of intensification, or the specific combination of HRT and SRT is not sustainable. A number of factors could be causing this observed instability including insufficient active fraction of biomass at the extended SRT, the biomass population is at an inflection point with shifting populations or an undefined stressor is impacting the population. Additional research will be required to explore the ultimate limits of intensification. What is apparent from the data in Table 1 is that in general IntensiCarbTM does not appear to significantly change the extent of digestion with the VSr ranging from 46-55 percent relative to the control at 50 percent. However, the rate of digestion is significantly enhanced by the increase in solids concentration, resulting in overall higher solids throughput rate and rate of methane generation increasing from 0.29 m3-CH4/m3-digester-day to a maximum of 1.08 m3-CH4/m3-digester-day (Figure 2). A challenge with most process intensification strategies deployed to date is the impact of metabolic byproducts on the process. Of particular interest is ammonia, as it is produced through the decomposition of proteins, which constitute a significant fraction of sludge materials. To date no technology has effectively managed ammonia-N in-situ, resulting in risks for process instability and or significant population shifts, as reported by Mah et al. (2017) for THP. The concentration of ammonia in digesters tested were very similar (Table 1). This is significant in that the control of ammonia in the digester could support high loadings without the negative impacts. Figure 3 simulates what solids concentrations sludge would need to be loaded at to a conventional digester to achieve the same degree of intensification and the resulting total ammonium concentration in the digester would be. What is apparent from the graph is that conditions similar to those observed in thermal hydrolysis would need to be achieved, but the resulting total ammonia concentrations would approach the current limits of those systems. Furthermore, the feed solids would need treatment to reduce the viscosity to make the material pumpable. Figure 4, presents the nitrogen balanced conducted across each system, showing significant removal of ammonium-N to the condensate of the evaporator from the digestate. Supporting the observation that the IntensiCarbTM process creates a unique condition where the negative impacts of ammonia can be directly controlled in a highly loaded digestion process. Furthermore, the condensate is a very clean liquid, devoid of solids making it an ideal solution for ammonia recovery and beneficial use; potentially eliminating the need for centrate treatment for nitrogen. The combination of reduced nitrogen load and stable operations suggest the peak capacity of the IntensiCarbTM process was not achieved, in these tests. Plotting the empirically derived peak loading conditions for common stabilization processes and the resulting average total solids load, at a volatile fraction of sludge equivalent to the one used in this study, it is possible to investigate potential peak loadings; assuming similar process limitations of peer processes. The IntensicarbTM process, as currently tested, would appear to have a similar capacity to thermophilic digestion (Figure 5) for loading. However, at the highest average loading condition, IF-3, no process instability was observed, suggesting further intensification could be possible and should be investigated. Overall, the IntensiCarbTM, based digestion process is early in development but is demonstrating promise and the novel application of vacuum is generating conditions within digesters that have not been evaluated to date. The combination of process intensification through decoupling SRT and HRT and the depression of ammonia-N concentrations would suggest the system may achieve further enhancement as optimal operating conditions are defined. Concurrent with the completion of these bench trials a pilot facility is being planned by the Great Lakes Water Authority to further vet this process. This pilot will investigate the scalability of the technology, introduce of real-world operating dynamics, further optimize operating conditions to define a design loading criterion and develop a techno-economic analysis. Vacuum enhanced anaerobic digestion represents a novel process for the intensification of anaerobic sludge stabilization. Potentially offering unique opportunities for resource recover, ammonia-N and dissolved methane, as well as providing a mechanism to alleviate the current limitations associated with anaerobic digestion, metabolic byproduct toxicity. If successful, this technology could provide the next step forward in resource recovery from sludges.

This paper was presented at the WEF/IWA Residuals and Biosolids Conference, May 16-19, 2023.

SpeakerMuller, Christopher

Presentation time

11:15:00

11:45:00

Session time

8:30:00

11:45:00

SessionSession 12: Innovative Processes in Anaerobic Digestion

Session number12

Session locationCharlotte Convention Center, Charlotte, North Carolina, USA

TopicResearch & Innovations

Author(s)

C. Muller

Author(s)C. Muller1, A. Khadir2, A. Al-Omari3, D. Santoro4, E. Jang5, K. Bell6, F. Okoye7, J. Norton8, X. Fonoll Almansa9, G. Nakhla10,

Author affiliation(s)Brown and Caldwell1; USP Technologies2; Wester University of Ontario3; Great Lakes Water Authority4

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date May 2023

DOI10.2175/193864718825158823

Volume / Issue

Content sourceResiduals and Biosolids

Word count13

Description: Intensifying Anaerobic Digestion with a Side-Stream Vacuum-Based Biosolids Treatment...

Intensifying Anaerobic Digestion with a Side-Stream Vacuum-Based Biosolids Treatment Technology: Process Validation Exceeding Expectations

Abstract

This study evaluates the application of a novel ex-situ vacuum-enhanced anaerobic digestion technology, referred to as IntensiCarbTM (IC), for process intensification through decoupling SRT from HRT, and ammonia recovery. Findings revealed that the IC sustain almost the same methane yield and COD destruction efficiency as the control at three times the organic loading rate (OLR). Furthermore, the ammonia concentration in IC- digester operating at 3 times higher organic loading was pretty much the same as the control, demonstrating the effectiveness of IC-technology in elutriating a large fraction of ammonia from IC-digester into the condensate. This leads to stable digester operation as well as a potential to generate revenue. The combination of high organic loading and low ammonia concentrations resulted in the prevalence of the higher growth rate Methanosarcinaceae in the IC-digester compared to the low growth rate Methanoseata predominance in the control.

A novel ex-situ vacuum-enhanced anaerobic digestion technology was evaluated for process intensification in anaerobic digesters. This technology, referred to as IntensiCarbTM (IC), could increase the OLR and volumetric loading by 3 times while maintaining stable methane yields and COD destruction. Ammonia recovery, reduced digester size, as well as reduced nitrogen loadings in sidestreams, are the major advantage of IC-technology.

SpeakerKhadir, Ali

Presentation time

13:30:00

13:50:00

Session time

13:30:00

15:00:00

SessionAdvances in Anaerobic Digestion and Sidestream Treatment

Session locationRoom S404a - Level 4

TopicIntermediate Level

Author(s)

Khadir, Ali

Author(s)A. Khadir 1; F. Omoye 2 ; E. Jang 3; D. Santoro 4; J. Walton 4; C. Muller 5; A. Al-Omari 6; K. Bell 7; G. Nakhla 8;

Author affiliation(s)Western University, Canada 1; Western University, Canada 2 ; USP Technologies, Canada 3; USP Technologies, Canada 4; USP Technologies, Canada 4; Brown and Caldwell, USA 5; Brown and Caldwell, USA 6; Brown and Caldwell 7; Western University, Canada 8;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2023

DOI10.2175/193864718825158983

Volume / Issue

Content sourceWEFTEC

Word count15

Lessons Learned from the Start-up of the TPAD Process at San Jose-Santa Clara RWF

Abstract

Temperature Phased anaerobic digestion, thermophilic digestion (55°C, 131°F) followed by mesophilic anaerobic digestion (38°C, 98°F), was the process selected by the San Jose-Santa Clara RWF (SJ-SC) as the stabilization process for the overall facilities expansion and modernization projects, with the purpose of renewing facilities, increasing operating capacity and starting the transition of SJ-SC away from the use of sludge lagoons to manage biosolids. TPAD was identified as the preferred digestion alternative at SJ-SC as part of the 2010 Biosolids MTPAD was identified as the preferred digestion alternative at SJ-SC as part of the 2010 Biosolids Master Plan. The TPAD process was formed based on converting four existing anaerobic mesophilic digesters to serve as the thermophilic anaerobic digesters and connecting that system to the existing 12 mesophilic anaerobic digesters through a sludge cooling heat exchanger system.

One of the first questions the start-up team had to answer was how to seed the digesters. The regionally relevant operating thermophilic digesters within proximity to San Jose are at the EBMUD Facility in Oakland, CA and the Hyperion WWTP in Los Angeles, CA. Given the large volumes of sludge and haul distances and schedule impacts it was elected to start the digesters from a mesophilic seed sludge.
The implications of starting with a mesophilic seed sludge are important to understand as they impact the startup schedule and duration to process maturity. The primary challenge is that the biomass operating in the system are not representative of a thermophilic operation. Following seeding, the temperature was increased rapidly to the target operating temperature of 55°C (131°F), with no sludge feed to the system. With the temperature increase there was a significant increase in the volatile acids concentration in the thin seed sludge, increasing from 100 mg/L as acetate to approximately 417 mg/L as acetate, over the first 12 days of operation, after which the VFA levels were rapidly depleted, decreasing from 403 mg/L as acetate to 7.92 mg/L as acetate between days 14 and 17. This was indicative of the reestablishment of methanogenic activity in the digester, indicating that thermophilic tolerant methanogens are present in mesophilic sludge and feed sludge as well, suggesting using thermophilic seed sludge is unnecessary. Loading commenced around day 20 of operations, which coincided with a rapid increase in volatile acid levels within the digester, resulting a cessation of feeding on day 32. After a decrease on VFA levels loading recommenced, which lead to a further spike in VFA. However, rather than ceasing loading the loading rate was held relatively constant, until there was a sharp decrease in VFA levels around day 50. The rationale for this strategy was to provide sufficient substrate to generate the needed VFAs to maximize methanogenic growth rate, while not souring the digester. This strategy proved successful as, loading increase steadily to a maximum of 50,000 lb-VS/d for the single digester at start up, without further uncontrolled imbalance between VFA production and loading rate (Figure 1). Concurrent with onset of stable loading, biogas production stabilized, producing measurable levels within the digester (Figure 2). Based on these observations, it took approximately 40 days from first heating the digester until full thermophilic digestion was established and in balance (Figure 2).

Similar trends were observed in the subsequent 3 digesters started up. Additional evaluation of the data found that daily change in volatile acids was means understanding digester progress towards as stabilized system. Figure 3, plots the daily change in volatile acids the start-up for Digester 8, concurrent with the digester observed VFA concentration, as measured by titration. What is apparent is that during the population stabilization period days 1-40, daily VFA generation remained positive, with the exception of the initial drop prior to any loading. However, once loading commenced the VFA generation (change VFA mass per day) remained above zero. However, with the onset of methanogenesis (~ day 50) increasing negative generation days were observed along with zero days. With the maturation of the biomass both structurally and in concentration it is expected that the VFA generation rate will converge around zero. Utilizing the daily change in VFA maybe an effective indicator of process maturation, both from an onset of methanogenesis and longer-term stabilization of the process.

Since commissioning the digestion process has provided significant additional operational design related lessons learned. Overall, since conversion to TPAD the volatile solids destruction has increased from a typical value of 30-40% to 55-60%, resulting in less solids and more biogas (Figure 4). Another critical observation was in the cooling heat exchangers, where there was significant accumulation of struvite, that impacted the ability of the system to cool the sludge in the mesophilic phase (Figure 5). Interestingly, mesophilic digester performance was not negatively impacted, even while operating at ~115°F, suggesting for future TPAD systems cooling all the way down to conventional mesophilic temperatures may not be necessary.
This paper benefits operators and design engineers alike will gain valuable insight into the TPAD process operations and benefits.

This paper was presented at WEFTEC 2025, held September 27-October 1, 2025 in Chicago, Illinois.

Presentation time

10:30:00

10:45:00

Session time

10:30:00

12:00:00

SessionLessons from Biosolids Project Startups

Session locationMcCormick Place, Chicago, Illinois, USA

TopicBiosolids & Residuals

Author(s)

Muller, Christopher, Alba, Alicia, Salerno, Lance, Nakamoto, Marc

Author(s)C. Muller1, A. Alba2, L. Salerno1, M. Nakamoto1

Author affiliation(s)Brown and Caldwell1, City of San Jose2, Brown and Caldwell

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2025

DOI10.2175/193864718825160146

Volume / Issue

Content sourceWEFTEC

Word count15

Performance Evaluation of Pilot Digestion Optimization Facility (PDOF) for Digestion Intensification of Metro Vancouver Anaerobic Digestion Facilities

Abstract

Introduction Anaerobic digestion has proven effective and reliable for stabilizing sludge for decades1. As municipalities grow, digestion intensification can offset or defer major capital expenditures. Testing operational limits for existing systems and trialing new technologies at full-scale carries considerable risk as potential process failures can lead to long recovery times or not meeting regulatory requirements. One approach to address these challenges is conducting bench-scale tests; however, a direct transition to full-scale can impose risks that were not fully considered at bench-scale. Metro Vancouver has built a Pilot Digestion Optimization Facility (PDOF) to conduct tests at a representative scale without risk to full-scale operations. The PDOF consists of three 8 m3 digesters that can be fed with mixed sludge or any combination of primary and secondary sludge. This paper presents results of the first three tests of a multi-year test plan: baseline digestion, thermophilic digestion and temperature-phased anaerobic digestion (TPAD). The test plan for 2023—2024 is outlined in Figure 1. Baseline digestion aimed to replicate the full-scale mesophilic digesters and achieve stable PDOF operation at various hydraulic retention times (HRTs) to identify the most comparable HRT to the full-scale digesters and to develop a volatile solids removal (VSr) performance curve. Thermophilic digestion will run two pilot digesters at 55 degrees C and 60 degrees C while the third runs at 38 degrees C as a mesophilic control. Stress tests will determine HRT operating limits. TPAD involves separating the digestion process into a fermentation phase in a separate tank from methane production. Higher temperatures (55 degrees C) in the first stage increase the rate of hydrolysis, while lower temperatures (38 degrees C) for the methane forming stage reduce energy input and maximize process stability2. The results of baseline digestion test are complete and discussed here. Results for the other tests will be available at the time of paper submission. Methods The PDOF is located at Lulu Island Wastewater Treatment Plant (LIWWTP) in British Columbia, Canada where two 5,400 m3 mesophilic anaerobic digesters operate with 25-to-30-day HRT. The PDOF feeds the same mixed sludge as the full-scale digesters to three 8 m3 pilot digesters. The PDOF was commissioned in June 2023 and achieved steady state mesophilic digestion after 8 weeks. Baseline digestion testing was conducted from July to September 2023. Performance data includes organic loading rate (OLR), VSr and destruction (VSD), biogas and methane yields, volatile fatty acids (VFA), alkalinity, ammonia, and microbial consortia. Genomic samples are collected, extracted and sequenced using shallow shotgun sequencing. Results Baseline Digestion Key process parameters for the pilot digesters were within 5 to 15 % of the full-scale digesters, suggesting direct scalability between the two. Figures 2—4 highlight the similarity between TS, VFA, and ammonia concentrations. The start-up period used diluted digested sludge and can be seen from June 2023 to mid-August 2023 when the digesters achieved steady-state operation. PDOF metrics including VSr and biogas yield were comparable to the full-scale digesters (Table 1). As biogas data from the test was not completely reliable due to condensate issues, the data reported here relies on measured chemical oxygen demand (COD) and a theoretical conversion of 0.35 standard litres of methane per gram of COD destroyed3. Following baseline digestion, modifications to the gas meters improved the accuracy for further tests. There was good agreement between the microbial consortia population in the pilot and full-scale digesters (Figure 5). Thermophilic digestion with LIWWTP sludge in the PDOF is expected to develop a completely new population as it is not seeded from thermophilic digesters. Thermophilic Digestion A single digester was transitioned to thermophilic temperatures (55 degrees C) without a thermophilic digestate seed by increasing the temperature instantly, with no added feed. To ensure that the thermophilic transition was progressing as expected, VFA and alkalinity were monitored daily (Figure 6). A second digester will be converted to 60 degrees C using different methods where mixed mesophilic sludge will be continuously fed to the digester. The two transition methods will be compared once complete. TPAD The test for TPAD is anticipated to be complete by the time of paper submission. Conclusions The three PDOF digesters demonstrated distinct individual performances according to their HRT during the steady-state period. All three digesters were stable throughout the tests based on digested sludge characterization. The VSr results for Digester B with 20-day HRT were closest to the full-scale digester with 28-day HRT. This may indicate that a scalability factor or inefficiencies at full-scale need to be considered in future tests. With the shorter HRT of Digester C (15 days), the product still meets the Organic Matter Recycling Regulation (OMRR)4 requirements for Class B Biosolids. In addition, this study provides valuable insights into the performance and scalability of the PDOF, operational limits for various digestion processes at reduced HRTs, and potential redefines the minimum requirements to achieve biosolids reguirements.

Anaerobic digestion stabilizes sludge effectively, and optimizing this process can save costs as municipalities grow. Intensified anaerobic digestion enhances efficiency, biogas production, and pathogen reduction via thermophilic digestion, advanced reactor designs, and pre-treatment methods. To test these processes, Metro Vancouver built the Pilot Digestion Optimization Facility (PDOF) at Lulu Island WWTP. This paper summarizes the early results from thermophilic digestion at 55 and 60 degrees Celsius.

SpeakerChegounian, Parisa

Presentation time

16:30:00

16:50:00

Session time

15:30:00

17:00:00

SessionAdvances in Anaerobic Digestion

Session number219

Session locationRoom 344

TopicBiosolids and Residuals, Intermediate Level, Research and Innovation

Author(s)

Chegounian, Parisa, Barber, Tyler, Kakar, Farokh Laqa, Martin, Kelly, Choy, Chris, Zaremba, Lillian, Gregonia, Theresa, Muller, Christopher, Yesin, Michael, Flibotte, Stephane, Yik, Susanna

Author(s)P. Chegounian1, T. Barber2, F. Kakar3, K. Martin4, C. Choy5, L. Zaremba1, T. Gregonia1, C. Muller6, M. Yesin2, P. Chegounian1, T. Barber2

Author affiliation(s)1Metro Vancouver, BC, 2Brown and Caldwell, British Columbia, 3, ON, 4Metro Vancouver, 5Metro Vancouver, 6Brown and Caldwell, MA

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2024

DOI10.2175/193864718825159667

Volume / Issue

Content sourceWEFTEC

Word count18

Description: Scalability of Anaerobic Digestion: Evaluating pilot scale operations for full-scale...

Scalability of Anaerobic Digestion: Evaluating pilot scale operations for full-scale implementation for Metro Vancouver's advanced digestion concepts

Abstract

Anaerobic digestion is a process central to the stabilization of sewage sludges while also proven to be the effective first step in many resource recovery programs. Mesophilic anaerobic digestion has proven efficient, effective, and reliable process for decades. However, with increasing capital costs, increased value of recovered resources and a societal push toward decarbonization, in an attempt to limit the impacts of climate change; interest in intensification of the digestion process has grown. In the past decade the adoption of intensified or advanced digestion processes has increased. Processes like thermal hydrolysis, thermophilic digestion and co-digestion have demonstrated that conventional process limits, performance and stability indices need to be reassessed and defined for the next generation of water resource recovery facility. Metro Vancouver, has experience with advanced digestion technologies, like its Class A series thermophilic anaerobic digestion system at Annacis Island, pioneering its adoption in the late 1990's. However, since its adoption and nearly 20 years of effective operations the true capacity limits of this process have yet to be defined. To define the operational limits of a biological process, a range of process metrics must be considered these include: - Substrate loading capacity. -Minimum solids retention time - Acclimation potential to inhibitory compounds - Process reaction rates - Dynamic stress responses and recovery (load, temperature, feed composition, toxicity, etc.) To elucidate these metrics at scale is possible, but the impacts of potential process failure can be significant, including long recovery times, process restart, loss of treatment and odors. Any of which can represent significant costs when managing thousands of cubic meters of material (millions of gallons). These risks further increase when new processes are being implemented and/or augmenting an existing digestion process. Further, testing new unproven technologies at scale that on paper would appear to be effective often prove to be more complicated than first envisioned, resulting in increased costs. These costs could result in a premature cessation of process development. One approach researchers and early adopters have addressed these challenges is through the bench testing, on-site and at universities. While these often provide evidence for proof of concept, they are limiting in scale and scope; often not integrating the true variability in operation that a full-scale facility, leading to conservative designs or non-adoption due to risk avoidance. Ultimately this slows the progression of technology advancement. Metro Vancouver, has elected to accelerate the testing and adoption of new processes for its wastewater treatment plants through the construction of the Pilot Digestion Facility (PDOF). This facility consists of three 8 cubic meter digesters, and a feed skid. The digesters are capable of operating at range of temperatures, retention times, mixing strategy and process phasing strategies. The PDOF not only allows for new processes to be tested but also existing systems to be stress tested to defined the maximum capacity of their existing assets. Further, at this scale, it is possible to test processes under real-world conditions, to better assess implementation at scale and process viability at scale. In June of 2023, the PDOF completed construction and commissioning and was started-up at the Lulu Island Wastewater Treatment Plant, in Richmond, BC. One of the first test plans implemented was to evaluate the reproducibility of pilot results relieve to the full-scale operating digesters. Three PDOF digesters were operated at solids retention times of 15, 20 and 28 days respectively on a mix of thickened primary (TPS) and waste secondary sludge (TWSS). Core process metrics were monitored to determine, system performance and compared to the full-scale operating digesters. Figure 1, shows the relationship between digester operating SRT and volatile solids destruction, after each of the three test digesters had reached stead-state and compared it to reference data and LIWWTP's current digester operations. What is apparent from the PDOF and the reference data is that 15 days SRT appears to be an inflection point around which further reduction in operating residence time will result in notable reduction in solids destruction which ties directly to biogas production. The current industry primary practice for resource recovery is biogas generation and methane utilization. Understanding this inflection point and being able to accurately test around this point will provide significant understanding of the total benefit of future process optimizations. Further what is also apparent is that the sludge a LIWWTP is more degradable than a 'typical' sludge, based on the reference data information. This is likely due to a combination of very low industrial input, high volatile content and a low overall residence time in the secondary system, a trickling filter solid contact system. The fact that the PDOF system produced similar VSr to the full-scale, suggests the system is performing in a similar manner to the full-scale digester, making extrapolations to full-scale relatively direct. In terms of reproducing the performance of the anaerobic digesters at LIWWTP, there was generally good agreement in the data, between the pilot and the full-scale digesters in terms of solids destruction, volatile acids, alkalinity and ammonia, Table 1. Biogas data was not completely reliable during this time as condensate was impacting meter accuracy on the pilot units. Modifications to the meter orientation, appears to have improved the response. As part of understanding the overall potential of anaerobic digestion and to gather further in-sites as to the fundamental mechanisms driving the observed results, microbial ecology analysis was conducted to understand changes in the consortia present. As part of this baselining observation the result of these efforts will be discussed. Figure 2, presents the relative abundance of different phylum level populations with time for each of the PDOF digesters and a single steady-state point for the LIWWTP digesters. Figure 3, further refines that focusing Euryarchaeota, which contain the methanogens. With the successful demonstration of the mesophilic operation of the PDOF facility, completing commissioning, the first tests of intensified digestion have commenced. The process being converted over to thermophilic operations to evaluate the limitations of the process. As of authoring the digester temperature has been increased and the microbial population is transitioning to thermophilic, as denoted by the significant increase in volatile acids and deterioration of biogas production. A process condition understood to be typical. Once steady thermophilic operation has been reached a range of process conditions will be tested. These include, reduced SRT and increased organic loading rate. This not only will demonstrate the potential for LIWWTP to utilize thermophilic digestion to increase capacity but also further define the capacity at the larger Annacis Island WWTP. This paper will discuss the results of the completed baselining operations, including lessons learned, and observation due to different operating retention times for mesophilic digestion. It will further present relevant observations from the conversion to thermophilic, which are in progress now.

This paper was presented at the WEF Residuals and Biosolids Conference, June 18-21, 2024.

SpeakerMuller, Christopher

Presentation time

09:30:00

10:00:00

Session time

08:30:00

11:45:00

SessionAdvancing Anaerobic Digestion

Session number12

Session locationOklahoma City Convention Center, Oklahoma City, Oklahoma

TopicAdvanced Treatment, Anaerobic Digestion, Intensification

Author(s)

Muller, Christopher

Author(s)C. Muller1, P. Chegounian2, L. Zaremba2, T. Gregonia2, T. Barber F. Kakar1, M. Yesin1

Author affiliation(s)Brown and Caldwell 1; Metro Vancouver 2; Metro Vancouver 2; Metro Vancouver 2; Brown & Caldwell 1; Brown and Caldwell 1;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Jun 2024

DOI10.2175/193864718825159467

Volume / Issue

Content sourceResiduals and Biosolids Conference

Word count18

Description: The Addition of FOG to Thermal Hydrolysis: Experiences of Hampton Roads Sanitation...

The Addition of FOG to Thermal Hydrolysis: Experiences of Hampton Roads Sanitation District's Atlantic Treatment Plant

Abstract

Advanced anaerobic digestion processes offer unique opportunities for process intensification, biosolids product production and resource recovery. Thermal hydrolysis is the current state of the art for digestion enhancement, commercially available, typically doubling the capacity over conventional systems. Co-digestion in conventional digesters has demonstrated that doubling biogas production is possible with the right mix and quantity. Combining THP with co-digestion has the potential to maximize the bioenergy yield from a fixed volume of digesters. Hampton Road Sanitation District (HRSD) as part of its recent upgrades to its 54 MGD Atlantic Treatment Plant added thermal hydrolysis (CAMBI) and FOG receiving to enhance energy generation and provide a much-needed outlet in the region for resource recovery from fats, oils and grease. HRSD installed two B-6-4 CambiTM thermal hydrolysis units at the plant which discharges thermally hydrolyzed sludge to its 6 mesophilic anaerobic digesters. HRSD had the option of FOG addition pre or post THP, but to preserve the Class A biosolids status the sludge pre-THP was selected as the process configuration. The introduction of FOG to THP requires that it achieve the same level of pre-treatment that the sludge entering it, screened to less the 5 mm and largely devoid of grit. Combining these technical requirements and lessons learned from site investigations of operating co-digestion programs a first of its kind FOG receiving station feeding THP was designed and commissioned. Figure 1, shows the general process flow of the FOG system. It was designed around the using the Envirocare Beast and a pair of heated storage tanks to raise the temperature of the FOG to 131°F prior to introduction to THP. Based on prior experience with FOG receiving station design and operations a coned bottom to the FOG storage tanks was incorporated to allow for the deposition of grit, removing it from the material fed to the THP units. The cone based design also allows for decanting and concentrating of FOG if needed; otherwise the storage tanks are completely mixed. The heated FOG is then introduced to the pulper of the THP system, in place of dilution water. An extensive characterization study by HRSD (see Table 1) of its FOG found that at an average of approximately 6% solids FOG would serve as good source of dilution water, while enhancing the energy value of the feedstock to the digesters. Since commissioning in the summer of 2021, the FOG station as operated reliably; however unanticipated repairs to FOG receiving facilities at other HRSD plants resulted in higher-than-planned FOG loading to AT throughout 2021 (Figure 2). As a result, the FOG facility at AT operated close to its peak week design basis (Table 1) nearly continuously through its startup and early operation period without undue mechanical or operational difficulties. Some early lessons learned during early operation include: - Rheological properties vary widely in high strength wastes. Screens and systems designed to process 6% FOG were able to manage 20% humus production waste - Introducing FOG to the pulper has proven reliable and viable means of maximizing the energy yield of the system. - Additional FOG water storage (or decanting, in some applications) may be a useful feature to allow additional capture of FOG through the dedicated receiving system in lieu of processing through the headworks are peak loading conditions. Storage, rather than material processing and biological processing, have proved to limit the capacity of the AT system at unanticipated high loading. Operations the THP and digesters has proven to be stable even with the high FOG loadings, demonstrating the viability of the unique microbial population attributed to THP pretreatment. This is critical in demonstrating the overall efficacy of THP to be integrated into a larger resource recovery and bioenergy program. Early biogas production numbers were hindered by system leakage but since correction, has been in line with the anticipated loadings. As part of the discussion of operations the acclimation of the digester to FOG and other high strength wastes will be discussed, as introducing FOG to a THP digester is not the same as a conventional digestion system which is inherently influenced by the feed sludge active biomass. Further at the time of presentation the THP system will have been shut down and restarted as part of it annual inspection and maintenance providing further information on the impacts of FOG and high strength waste loadings on the THP process. But also provide information on the recovery of the biological process and a return to full loading under a co-digestion scenario. Overall this information is important as the adoption of THP increases across North America and little information is currently available surrounding the integration of co-digestion with THP. At the time of presentation nearly a year's worth of data and lessons learned will have been collected and presented.

This paper was presented at the WEF Residuals and Biosolids Conference in Columbus, Ohio, May 24-27, 2022.

SpeakerMuller, Christopher

Presentation time

16:15:00

16:45:00

Session time

13:30:00

16:45:00

Session number12

Session locationGreater Columbus Convention Center, Columbus, Ohio

TopicAnaerobic co-digestion, FOG, Thermal hydrolysis

Author(s)

C. Muller

Author(s)C. Muller1; C. Wilson2

Author affiliation(s)Brown and Caldwell; 1Hampton Road Sanitation District; 2

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date May 2022

DOI10.2175/193864718825158446

Volume / Issue

Content sourceResiduals and Biosolids

Word count17

Description: The IntensiCarbTM Technology as High-Rate Process for Anaerobic Biosolids...

The IntensiCarbTM Technology as High-Rate Process for Anaerobic Biosolids Fermentation Intensification and Nutrient Recovery

Abstract

The IntensiCarbTM Technology as High-Rate Process for Anaerobic Biosolids Fermentation Intensification and Nutrient Recovery Gholamreza Bahreini1, Masuduz Zaman1, George Nakhla1, Kati Bell2, Christopher Muller2, Jose Jimenez2, Ahmed Al-Omari2, Domenico Santoro3, Eunkyung Jang3, John Walton3, Frances Okoye4, Farokh Laqa Kakar4, Elsayed Elbeshbishy4, Ferenc Hazi5, Imre Takacs5, Sudhir Murthy6, Diego Rosso7,8* 1Department of Civil and Environmental Engineering, Western University, CANADA 2Brown and Caldwell, USA 3USP Technologies, CANADA 4Environmental Research for Resource Recovery Group, Department of Civil Engineering, Ryerson University, CANADA 5Dynamita, FRANCE 6NEWHub Corp, USA 7Civil & Environmental Engineering Department, University of California, Irvine, USA 8Water-Energy Nexus (WEX) Center, University of California, Irvine, USA *Corresponding author (e-mail: bidui@uci.edu) Abstract: The performance of an innovative vacuum-driven mesophilic anaerobic fermentation technology for the treatment of municipal biosolids was compared against a conventional fermenter. Each system was fed by a 50:50 v/v mixture of primary and thickened waste activated sludge (TWAS). The vacuum driven fermenter allowed for nearly complete decoupling of hydraulic retention time (HRT) and solids retention time (SRT). Two testing conditions with intensification factors (IF), defined as SRT/HRT, of 1.33, and 2.00, were tested. Results indicated that the vacuum-driven technology could simultaneously reduce the reactor size significantly (half of the control volume), while also enhancing process yields and nutrient partitioning between fermented solids, fermented liquid, and condensate. Specifically, relative to the conventional fermenter, the yields of volatile fatty acids for the vacuum-driven fermenter were enhanced by 29.5% (IF=1.33) and 73.8% (IF=2.00). Additionally, the hydrolysis yields increased substantially reaching 280 mg ˆ†sCOD gVSS-1 (IF: 1.33), and 321 mg ˆ†sCOD gVSS-1 (IF: 2.00), compared to 241 mg ˆ†sCOD gVSS-1 in the conventional fermenter. Specific denitrification rates using the fermentates as a carbon source were comparable with acetate. Keywords: Anaerobic Digestion; IntensiCarb Technology; Resource Recovery Introduction Sewage sludge management accounts for almost one-half of the total sewage treatment cost. Anaerobic digestion, one of the most widely used sludge stabilization and waste management techniques (Appels et al., 2008; Nguyen et al., 2021) is credited with additional energy and nutrient recovery. Contrarily, due to high solids content and complex structure, large digester volume and long SRTs are needed (Neumann et al., 2016). The vacuum-driven IntensiCarb (IC) technology (a trademark of USP Technologies) is a promising alternative to conventional anaerobic digestion of wastewater biosolids as it reduces digester volumes, transportation and energy consumption, while it increases the volatile solids removal (VSR) efficiency and facilitates separate recovery of ammonia, volatile fatty acids, and phosphorus. This process evaporates water under negative pressures and at low temperatures, which completely decouples HRT from SRT, allowing residual solids to be retained longer in the reactor, resulting in enhancement of hydrolysis and acidification of particulate organic matter. Application of vacuum pressure during IC operation also potentially can enhance the process through change in partial gas pressures in the reactors which affects dark fermentation metabolic pathways (Rajhi et al., 2016). The IC technology can effectively divert the recovered resources into separate streams by stripping almost 50% of ammonia in the condensate, while retaining the carbon (VFAs) in the fermented sludge. The concept of decoupling SRT/HRT through vacuum makes the technology more accessible to a broader range of utilities, including small municipalities as it increases the volumetric and solids loading per unit reactor volume. The evaluation of the impact of the vacuum-induced fermentation was one of the main objectives of this project. Additionally, assessment of the quality of the fermentate as supplemental carbon source for biological nutrient removal was also tested in this research. Material and methods A bench-scale IntensiCarb system (Figure 1) with operating volume of 3L was placed on a pre-calibrated induction heater connected to a vacuum pump and operated in parallel to a conventional fermenter (2L). Both ferementers were fed with 50/50 (on volumetric basis) primary and thickened waste activated sludge from the Greenway WRRF (London, ON). Operating temperature and pressure were maintained and monitored at 45 °C, and around 1015 mbar during fermentation. Vacuum was applied once per cycle intermittently at differential pressure of -900 mbar (equivalent temperature of 45 °C) for 4, and 10 hours for IC stage 1, and stage 2, respectively. System pressure and temperature of IC were continuously monitored during vacuum. The reactors were fed daily and fermented sludge was wasted daily to maintain the respective HRTs (1.50-2.25 days), while SRT was fixed at 3.0 days. Operations at conventional, IC (stage 1), and IC (stage 2) were continued until reaching to stabilized steady state condition (Î” YieldVFA ‰¤5%). Results and Discussion Cumulative VFA and soluble COD of the fermentates were plotted against influent VSS fed to the fermenters (Figure 2). Results indicate stabilized performance of the reactors with good correlations between cumulative parameters (R2>0.99) at steady state for all the tested conditions. The production yields calculated at different phases of the experiment are summarized in Table 1. As shown, operation of the reactor with the IC technology resulted in 29.5% and 73.8% increase in VFA yield (IF of 1.33, and 2.0), respectively, compared to the conventional fermenter. Additionally, the hydrolysis yield of the conventional fermentation, was enhanced by 16.2% and 33.2% through IC operation. VFA generation rate measured per unit biomass in the reactors were 28, 33, and 39 mg Î”VFA gVSSr-1 d-1 for the conventional, IC (IF: 1.33), and IC (IF: 2.00) reactors respectively. These values show the enhancement of the process in the IC reactors over the conventional fermenter (Figure 3). Thus, the IC technology not only increased volumetric and solids loadings from 0.34 (m3sludgem-3fermenter d-1), and 4.2 (kgVSS m-3fermenter d-1), to 0.44, and 0.67 (m3sludge m-3fermenterd-1), and 5.4, and 10.1 (kgVSS m-3fermenterd-1), for IC reactors operated at stage 1, and 2, respectively; resulting in processing of biosolids in significantly smaller fermenters; but also improved the VFA and SCOD yields as proven in this study (Table 1). In a typical WRRF processing 1 ton d-1 of mixed PS/TWAS, operation of an IC fermenter (IF:2.00, SRT:3 d) can reduce the fermenter size by 25% (from 3 to 2.25 m3), while increasing the VFA production by 73% (from 760 to 1330 g VFA d-1). Results from batch denitrification tests using fermentate and acetate as carbon source revealed biomass-specific maximum denitrification rates of 0.28, and 0.24 mg NO3-N mgVSSRAS-1 d-1 for acetate and fermentate, respectively, indicating a comparable denitrification potential of the fermentate as an ideal carbon source like acetate. Conclusions Intensified fermentation using the vacuum-based IntensiCarb technology could simultaneously enhance fermentation and resource recovery as well as reduce fermenter size compared to conventional fermenters. The IC fermentate showed comparable specific denitrification rates to acetate. The outcomes of this study clearly showed the tremendous potential of the vacuum-driven fermentation to reduce cost and enhance performance of the widely used anaerobic wastewater biosolids fermentation.

This paper was presented at the WEF Residuals and Biosolids Conference in Columbus, Ohio, May 24-27, 2022.

SpeakerMuller, Christopher

Presentation time

14:00:00

14:30:00

Session time

13:30:00

16:45:00

Session number14

Session locationGreater Columbus Convention Center, Columbus, Ohio

TopicAnaerobic Digestion, IntensiCarb Technology, Resource Recovery

Author(s)

C. Muller

Author(s)M. Zaman1; G. Bahreini2; G. Nakhla3; K. Bell4; C. Muller5; J. Jimenez6; A. Al-Omari7; D. Santoro8; F. Okoye9; F. Laqa10; E. Elbeshbishy11; F. Hazi12; I. Takacs13; S. Murthy14; D. Rosso15

Author affiliation(s)Residuals and Biosolids Speaker; 1Residuals and Biosolids Speaker; 2Western University; 3Brown and Caldwell; 4Brown and Caldwell; 5Residuals and Biosolids Speaker; 6Residuals and Biosolids Speaker; 7

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date May 2022

DOI10.2175/193864718825158432

Volume / Issue

Content sourceResiduals and Biosolids

Word count15