Higgins, Matthew, Higgins

Higgins, Matthew

Matt Higgins is Professor and Claire W. Carlson Chair in Environmental Engineering at Bucknell University and is currently the Faculty Director for the Bucknell Center for Sustainability and the Environment. His research has largely focused on biosolids issues including digestion, co-digestion, thermal hydrolysis, conditioning and dewatering, odors and reactivation and regrowth of indicators and pathogens in biosolids.

Titles from this speaker

Description: Alternate: Evaluating Feasibility of Implementing Co-digestion at San Francisco...

Alternate: Evaluating Feasibility of Implementing Co-digestion at San Francisco International Airport

Abstract

Background: This study was performed to evaluate feasibility of implementing co-digestion at San Francisco airport facility (SFO) in California. The overall objective was to obtain preliminary feasibility information regarding diverting organic wastes from the terminal restaurants to its wastewater treatment plant anaerobic digester to enhance biogas production for beneficial use. The study included preliminary regulatory, technical, economic as well as triple bottom-line evaluation. The key objectives of the study included evaluating i) how much organic waste can be added to the airport's anaerobic digester without impacting the digester stability, ii) can all of this capacity be met with the organic wastes generated at the airport, iii) how much biogas will be generated during co-digestion, iv) what are the potential beneficial uses for the quantity and quality of biogas produced that are in alignment with the airport's sustainability goals as well as current and impending regulations, v) what are the potential impacts (e.g. increase in wet cake, polymer demand, metals in biosolids) of this process, and vi) what is the preliminary cost estimate for this program. Regulatory Review: Regulatory evaluation included review of SFO's existing wastewater treatment plant permit requirements (e.g. effluent discharge, emissions) as well as recent changes to co-digestion related regulations. A review of the permits indicated i) discharge limits for ammonia, organics and select metals, and emissions limit for ammonia, select organics and hydrogen sulfide (H2S). The bench scale studies were designed to partially address impacts of co-digestion on these limits. Among the new/emerging regulations, the 'Advanced Clean Fleets' (ACF; Release #23-13) regulation put forward by California Air Resources Control Board (CARB) and approved by the State in 2023 requires all the heavy and medium duty vehicles to be phased out and replaced with zero emission vehicles (ZEV) within the next 20 years. This will have a significant impact on the use of biogas for vehicle fuel. Further, a proposed CARB amendment to suspend Low Carbon Fuel Standard (LCFS) incentives, if implemented, will further discourage pipeline injection of treated biogas (Renewable Natural Gas (RNG)). The impact of these and other regulations were taken into consideration during evaluation of beneficial use alternatives for biogas. Bench Scale Testing: A bench scale test was performed using the TWAS from the airport full scale sequential batch reactors and the organic waste from the airport restaurants to address various objectives of this study. The organic wastes were collected as mixed waste which was then extracted using a Thor process for addition to bench scale reactors. The wastes and TWAS were characterized for organic and inorganic constituents, including metals concentration. The data indicated that the organic content (COD) and degradable solids (VS) were much higher in the food waste than those for TWAS. The COD of the TWAS and organic wastes were approximately 48,000 and 245,000 mg/L respectively. The total and volatile solids of the TWAS were 4.6 and 82%, respectively and the total and volatile solids of the organic waste were 21 and 88%, respectively. Four 10 Liter bench scale digesters filled with 8 L of TWAS and appropriate amount of food waste was used in the bench scale studies (Figure 1). One of the digesters (Control) received only the TWAS. The other three digesters (R1, R2 and R3) received food waste at 20, 40 and 60% of volatile solids as the TWAS volatile solids content. On a volume basis the food waste added was 4.3, 8.3 and 12.25% of the TWAS volume in the three digesters, respectively. The digesters were operated in the anaerobic digestion lab (ADL) at Bucknell University (Lewisburg, PA) at 37 oF. Various operating parameters and biogas quality and quantity were measured during the four-month study. The bench scale data indicated that the control digester (i.e. TWAS-only) produced approximately 6,000 mls/day of biogas whereas the digester with the highest amount of food waste produced approximately 14,000 mls/day of biogas Figure 2). In addition to total biogas production, the biogas yield, i.e. the cubic feet of biogas produced per pound of volatile solids reduced also were higher for the food waste added digester. The biogas yield of the control and the highest food waste added digesters were 35.5 and 47 cu.ft./lb VS reduced, respectively. These data indicated that, the food waste was digested more readily than the TWAS and produced significantly higher amount of biogas at a much smaller volume added. Addition of food waste increases the solids added to the digester. This, in turn, may increase the amount of dewatered cake generated after digestion. Hence, dewatering studies were conducted using the digested sludge from the bench scale study. The data indicated that the net wet cake mass may decrease by about 7% at the loading used in R1 digester and increase by approximately 8 and 12% at the loading used in the R2 and R3 digester, respectively (Figure 3). Projections for Full Scale Operation: The bench scale study data was then used to project various parameters for the airport's full scale co-digestion operation. The evaluations indicated that nearly 1,900 tons of organic waste is required annually for the co-digestion process at the desired (food waste at 60% VS of TWAS VS) loading rates. The airport generates approximately 4,500 tons of organic waste each year. Hence, enough organic waste is available for co-digestion. Further, sufficient volume is available in the digester to receive the food waste is diluted up to 7% solids content for ease of pumping. This operation is estimated to produce approximately 38 to 45 standard cubic feet per minute (scfm) biogas. Based on bench scale data, addition of this amount of food waste may increase the dewatered cake produced by 1.3 wet tons per day and the polymer demand for dewatering by approximately 19.5 lb/day. A preliminary evaluation of regulatory compliance, limited to the data from the bench scale study, indicated compliance requirements for the tested parameters may be met after food waste addition to the digester. However, more detailed evaluation through a larger scale study and detailed discussions with regulatory agencies may be required during the next phases of the study to ensure compliance with regulatory requirements. Evaluation of End Use Alternatives: The above information/data were used to evaluate beneficial use alternatives for the biogas produced through co-digestion. The alternatives evaluated include i) combustion-based combined heat and power (CHP) generation technologies such as internal combustion engines (IC Engine) and microturbines, ii) non-combustion CHP technologies such as fuel cell systems and linear generation technology, iii) use of biogas for vehicle fuel, and iv) pipeline injection of treated biogas. The airport does not prefer combustion-based technologies due to environmental concerns. Further, the current and impending CARB regulations do not favor the use of biogas for vehicle fuel or pipeline injection in the long term. The non-combustion CHP technologies, while relatively new to the market, have made significant advancements in the recent years. Further, they produce much lower greenhouse gas emissions. Hence, these non-combustion technologies (fuel cell and Linear Generation) are recommended for further evaluation in the next phase for potential installation at the airport. Preliminary Cost Evaluation: A preliminary cost evaluation was performed for the implementation of the proposed program. The airport is currently evaluating its options for food waste collection, sorting and processing. Hence, the evaluation did not include food waste collection, extraction, storage and pumping to the digester. The preliminary cost estimate for the rest of the constituents (CHP, biogas treatment and installation, etc.) is approximately $2.95 M. The increased annual O&M cost is approximately $180,000/year. The estimated revenue from the savings in electricity is approximately $ 270,000/year. Triple Bottom-Line Evaluation: Further, a triple bottom-line cost-benefit analysis (financial, social and environmental) was performed for the proposed technology. The evaluation indicated that in the next twenty years the proposed technology will avoid a total of approximately 19,500 tons of CO2e emissions, mainly from diverted waste and fertilizers offset. It is also estimated that the proposed technology will mitigate emissions of approximately 5,200 pounds of contaminants through avoided natural gas purchases. No avoided emissions due to electricity generation is anticipated since SFO already purchases clean energy from San Francisco Public Utility Commission.

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

SpeakerRajagopalan, Ganesh

Presentation time

13:30:00

15:00:00

Session time

13:30:00

15:00:00

SessionConsiderations for Long-Term Biosolids Planning

Session number5

Session locationBaltimore Convention Center, Baltimore, Maryland, USA

TopicAnaerobic co-digestion, Biomethane, Lipids/proteins/carbohydrates ratio, TWAS, Manure, SSO, Biosolids treatment, Circular Economy, Co-Digestion With Other Organic Sources, Market Analysis, Master Planning, PFAS/Emerging Contaminants, Resiliency, Resource Recovery, Sustainability, Triple Bottom Line Plus

Author(s)

Rajagopalan, Ganesh, Higgins, Matthew, Hummel, Michael, Mahoney, John, Cooke, Erin

Author(s)G. Rajagopalan1, M. Higgins2, M. Hummel3, J. Mahoney4, E. Cooke5

Author affiliation(s)AECOM, 1Bucknell University, 2Stok, LLC, 3Tanner Pacific, 4San Francisco International Airport, 5

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date May 2025

DOI10.2175/193864718825159745

Volume / Issue

Content sourceResiduals and Biosolids Conference

Word count12

Description: Impacts Of Intermediate Thermal Hydrolysis Pretreatment (iTHP) on Anaerobic...

Impacts Of Intermediate Thermal Hydrolysis Pretreatment (iTHP) on Anaerobic Digestion, Dewatering, and EPA VAR Requirements

Abstract

Introduction
Thermal hydrolysis pretreatment (THP) of sludges prior to anaerobic digestion utilizes high temperature and pressure (typically 165 oC, 6 bar, 30 min) to solubilize material and break down the solids which greatly reduces viscosities and enhances digestion and dewatering. The reduction in viscosity allows much higher loading rates and intensification of the anaerobic digestion process. In addition, the thermal treatment greatly exceeds the EPA time-temperature requirement for meeting Class A biosolids (EPA, 2003), and eliminates issues with reactivation and regrowth of pathogen indicator bacteria (Higgins et al., 2008). Typically, THP is performed prior to anaerobic digestion. The intermediate THP (iTHP) process can be employed in which the THP is applied after a primary anaerobic digestion step and before the secondary digestion process. The process flow diagram for conventional THP and the iTHP processes are shown in Figure 1. Intermediate THP has the advantage of reduced size of the THP process (and lower capital costs), plus the benefits of intensification and potentially improved dewatering as well as meeting Class A biosolids time-temperature requirement. Since much of the readily degradable material would have been removed in the first digestion step, it is possible that the volatile solids reduction (VSR) of the second digestion step after iTHP could be below the EPA vector attraction reduction (VAR) rule which requires a 38% VSR which 'â€¦must be met after or concurrent with pathogen reductionâ€¦' (EPA, 2003). As an alternative, the EPA allows compliance with the VAR requirement if the process can demonstrate 'â€¦less than 17% additional volatile solids loss during ben-scale anaerobic batch digestion of the sewage sludge for 40 additional days.' This is known as Option 2 in the VAR options.
Several studies have examined iTHP and shown the efficacy of the process to improve overall digestion by increasing biogas and VSR as well as reduce costs (Rus et al., 2017; Bjerg-Nielsen et al., 2017); however, limited research has been performed on meeting the EPA VAR as well as evaluating downstream impacts such as final dewatering. Objectives The objectives of this research were to investigate the impact of iTHP on digestion and the EPA VAR requirements as well on downstream processes.
Methods and Materials
Samples of dewatered cake after the first stage digestion (SRT = 25 d) were shipped to Bucknell University where they were thermally hydrolyzed (165 ÂºC, 6 bar, 40 min). The thermally hydrolyzed solids were fed to a laboratory scale digester with an active volume of 8 L, and an SRT of 10 days, see Figure 2. The target feed concentration was 10% TS. The anaerobic digesters were housed in a temperature-controlled room held at 38 oC, and were fed once per day (semi-continuous operation) to achieve the desired SRT. The digester performance was monitored on a regular basis for typical parameters such as pH, TS/VS, COD, alkalinity, gas production, etc. The digesters were operated until steady state conditions were achieved as determined by stability in the different operating parameters. Figure 3 shows the digester TS and VS concentrations during the study, and the steady state period was considered to be from days 40 through 70. The values of the different parameters during the steady state period were averaged to determine average steady state values. During the steady state period, waste samples from the digester were used to perform the 40 d additional VSR test as stipulated by the EPA VAR requirements. Over a four-week period, samples from the digester were placed in triplicate serum bottles and every 10 days the samples were analyzed for TS/VS, COD and ammonia until day 40. At the end of the study, the digestate was dewatered using a lab scale dewatering method.
Results and Discussion Digestion Performance.
Table 1 summarizes the results from the digester study. The average VSR of the with the THP and digestion processes was about 28% using the Van Kleek method. This is below the 38% requirement for VAR; however, the first digestion stage at the plant achieves an average VSR of around 50%, so this is additional VSR after the conventional digestion. When considering the addition VSR for the iTHP process, the total VSR through the entire process is about 63%. The overall gas production would be increased by over 25% by implementing the iTHP process compared to the conventional mesophilic digestion.
EPA VAR Requirements.
Although the total system meets the 38% VAR requirement, the EPA regulations stipulate for thermophilic process used to achieve Class A biosolids, the VAR step must occur either simultaneously or after the thermophilic treatment. In this case with iTHP, the VAR is occurring after the thermophilic treatment, and it does not meet the 38% VSR requirement, which is a bit of a gray area in the regulations. The 40 d additional VSR test can be used to definitively meet this rule as long as the additional VSR is less than 17%. Based on the four different additional VSR tests that were performed (each in triplicate), the average additional VSR was 5.8% with a standard deviation of 3.5%, which is well below the maximum value of 17%.
Dewatering.
A dewatering test was performed at the end of the study, and the average cake solids was 21.4%, which is on the lower end for typical THP sludges, but still an improvement of the 18% cake solids currently achieved at the plant. The digestate had a relatively high reactive phosphorus concentration which has been shown to decrease dewaterability (Higgins et al., 2004). Based on the cake solids and the additional VSR, the total mass of wet cake leaving the plant would be reduced by about 50%, resulting in significant savings from hauling costs. The cake odorant production during storage was quite low, with a peak total organic sulfur concentration of 55 ppmv, which is quite low.
Summary
Application of the iTHP process had several benefits: 1. increased overall VSR from about 50% to 63%; 2. increased biogas production by 25%; 3. meets EPA Class A time-temperature requirements and VAR requirements; 4. reduced the overall wet cake mass leaving the plant by about 50%. The full paper will include a more detailed discussion of the methods and results as well as an economic comparison of THP, iTHP and conventional mesophilic digestion.

A study was performed to evaluate the effect of intermediate thermal hydrolysis pretreatment (iTHP) which utilizes THP after a primary stage of anaerobic digestion and prior to second stage digestion. The effect of iTHP on overall VSR, dewatering and cake quality were evaluated. The iTHP process increased overall VSR from about 50% to 63% and improved cake solids by about33%. This improved VSR and dewaterability would reduce the wet cake mass leaving the plant by about 50%.

SpeakerHiggins, Matthew

Presentation time

16:00:00

16:15:00

Session time

15:30:00

17:00:00

TopicIntermediate Level, Biosolids and Residuals, Energy Production, Conservation, and Management, Facility Operations and Maintenance

Author(s)

Higgins, Matthew

Author(s)Matthew Higgins1; Steven Beightol2; William Barber3; Kine Svensson4

Author affiliation(s)Bucknell University, Lewisburg, PA1; Bucknell University, Lewisburg, PA2; Cambi, Malvern, PA3; Cambi, Asker, Norway4

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2022

DOI10.2175/193864718825158705

Volume / Issue

Content sourceWEFTEC

Word count16

Market Value for Various Biosolids Products from Innovative Biosolids Technologies (WRF Project #5169)

Abstract

...Introduction: Biosolids are an organic and nutrient-rich product that are an important and valuable resource than can be used beneficially to support the advancement of the circular water economy. However, the market for the beneficial use of biosolids has been increasing challenged by concerns regarding high cost and limited land application opportunities, public perception, and contaminants of emerging concerns (CECs), such as per- and polyfluoroalkyl acids (PFAS) and microplastics. In response to these rising challenges, a range of innovative biosolids management alternatives have been emerging that can help utilities overcome some of these challenges. To comprehensively understand the potential of innovative biosolids management alternatives to address these challenges, a holistic evaluation framework (...Figure 1) was developed. ...Objective: The information presented provides valuable and practical information to utilities including: 1) definition, function, and level of readiness of innovative biosolids treatment technologies and 2) a market assessment and value of the various end products identified through the technology screening. The proposed presentation will inform utilities of emerging technologies to address specific challenges, offer insight to different end-products from innovative technologies, and provide an assessment of diverse end-products from an aggregated dollar value perspective. ...Status: The project is funded by the Water Research Foundation (WRF 5169) and will produce an adaptable tool that utilities can use to select suitable, practical, and sustainable innovative technologies for implementation. The project is ongoing and will be completed the second half of 2024. Three of the six tasks have been completed. ...Methodology: The comprehensive technology review and evaluation gathered information from more than 140 references, including published literature (focused on peer-reviewed literature), gray literature (information from vendors, including WRF's TechLink), information from various associations, and responses from an online survey. Once the initial number of innovative technologies was compiled, several screenings were conducted to determine applicability and if it would advance to further evaluation. Technologies captured from the comprehensive search were required to provide at least one of the following benefits compared to established technologies to be considered as 'innovative technology.'

*Reduce biosolids quantity.

*Improve end-product quality.

*Enhance energy generation.

*Reduce greenhouse gas emissions.

*Reduce emerging contaminants. The findings from the initial evaluation were then screened to determine whether the technology is classified as 'innovative,' in alignment with the definition developed by the EPA (1). The innovative biosolids management technologies identified produce a variety of valuable products. To assess the markets for these products, an evaluation was conducted comparing the value of these end products to a standard of Class A/EQ dewatered cake. The suite of end products evaluated is presented in Table 1. Information was gathered from various sources including scientific journal articles, industry reports, technology vendors, characterization data, and professional experience. End-products, including a baseline product of Class A/EQ dewatered cake, were assessed on the following categories:

*Inherent Value

*Market Suitability / Access

*Cost of Management / Market Value

*Contaminants of Emerging Concern Removal ...Findings Following the initial screening 35 technologies met the defined criteria for innovation, seen in ...Table 2. The results from this evaluation will be presented on an accessible interactive dashboard for utilities and other interested parties (...Figure 2). The presented information will include definitions, fact sheets, benefits to existing technologies and more. The innovative technologies identified resulted in a variety of end products that were further evaluated in the context of the existing market. To contextualize the value of the various end products, they were evaluated from a cost perspective, specifically aggregated dollar value of nutrients and carbon, shown in ...Figure 3. On a per-dry ton basis, biochar and struvite have the highest inherent value (...Figure 3), and biochar has value in the greatest number of constituents/properties, suggesting a relatively wider market applicability. Market access (...Table 3), which is based on professional opinion/experience, assigns a score of 0 (low access) to 1 (high access) and supports the assertion that biochar has wide market access. The 'net market benefit' (...Figure 4) equals the market access score multiplied by the average cost of management and expresses the potential for cost recovery. The results of the market evaluation clearly show the positive net market benefit of end products from innovative biosolids management technologies in comparison to the baseline Class A/EQ biosolids. Each end product greatly reduces costs to the utility compared to Class A/EQ biosolids, and often even had potential to bring revenue to the utility. The identified innovative biosolids treatment technologies can diversify end product outlets by providing a wider range of accessible markets.

The information presented aims to provides valuable and practical information to utilities through a market assessment and valuation of the various end-products identified through the technology screening. The results will inform utilities of emerging technologies to address specific challenges, offer insight to different end-products from innovative technologies, and provide an assessment of end-products from an aggregated dollar value perspective.

SpeakerLewis, Asa

Presentation time

16:00:00

16:30:00

Session time

15:30:00

17:00:00

SessionPFAS in Biosolids: Remove and Track it

Session number417

Session locationRoom 238

TopicBiosolids and Residuals, Intermediate Level, PFAS

Author(s)

Lewis, Asa, Evans, Christian, Teshima, Mark, Sun, Yian, Abu-Orf, Mohammad, Knowles, Paul, Higgins, Matthew, Blate, Micah

Author(s)A. Lewis1, C. Evans2, M. Teshima2, Y. Sun3, M.M. Abu-Orf1, P. Knowles4, M.J. Higgins5, M.D. Blate1

Author affiliation(s)1Hazen and Sawyer, PA, 2Sylvis Environmental, BC, 2, 3Hazen and Sawyer, CA, 4Hazen & Sawyer, NY, 5Bucknell University, PA

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2024

DOI10.2175/193864718825159578

Volume / Issue

Content sourceWEFTEC

Word count14

Description: Pushing Feed Rates Beyond "Limits" to Accelerate THP Digestion...

Pushing Feed Rates Beyond "Limits" to Accelerate THP Digestion Startup: Insights from an In-Situ Pilot Study

Abstract

Introduction
Thermal hydrolysis pretreatment (THP) has been gaining popularity for intensifying the anaerobic digestion (AD) of municipal wastewater sludge by decreasing sludge viscosity, enhancing solids reduction, and boosting biogas production [1, 2]. The digested sludge also gains significant improvement in dewaterability, and the dewatered Class A biosolids are qualified for direct land application [3-5]. However, the startup phase for THP-enhanced digesters remains risky and time-intensive due to improved hydrolysis and faster acid production, as well as longer time needed to achieve shorter solids retention times (SRT). Current industry norm for digester feed rates during startup, typically ranging from 0.10 to 0.25 lb COD/lb VS/day, often lead to a prolonged timeframe to achieve full digester throughput capacity. To address this limitation, this study explored the possibility to further increase maximum feed rates to a level that are at least twice the industry norm, aiming to accelerate the startup of THP-enhanced digesters. A total of three maximum feed rates, namely 0.31, 0.33, and 0.38 lb COD feed/lb VS digester/day, were tested with the hope to investigate the upper boundary of startup pace achievable with a commonly adopted full-scale startup strategy for THP-enhanced digesters.
Materials and Methods
Samples of thickened primary sludge (TPS) and waste activated sludge (WAS) were mixed at a target dry mass ratio of 3:2 and then pre-dewatered to a TS content of 16% total solids (TS) with a cationic polymer using a pilot-scale screw press thickener. The pre-dewatered cake samples were processed through a pilot-scale THP unit (Cambi, Asker, Norway) operated at 6-bar steam pressure (equivalent to 165 C) for 30 minutes. The pretreated sludge was diluted to 9% TS and fed daily into three pilot-scale mesophilic (36.5 C) digesters with a 10 L working volume and a target SRT of 15-day.
To simulate the future startup protocol for full-scale operations, each pilot digesters was initially filled to 30% full (v/v, 3 L) which is just enough for initiating the mixing, with 20% (v/v, 2 L) filled with tap water and the other 10% (v/v, 1 L) seeded with full-scale THP-enhanced mesophilic AD sludge freshly collected from a local plant. The headspace in the digesters were purged with nitrogen gas before feeding started.
Results and Discussion
The startup plan illustrated in Figure 1a consisted of three phases. In Phase 1, the goal was to acclimate the seed to the new feed sludge produced at the Arlington WPCP. The initial feed rate on Day 1 used in all three digesters was 50% of the steady-state feed rate of the seed digester, or around 0.11 lb COD feed/lb VS digester/day. The feed rates were ramped up at 8% per day until reaching the maximum feed rates designed for this study, namely 0.31, 0.33, and 0.38 lb COD feed/lb digester VS/day (Table 1). As can be seen in Figure 2a, the actual feed rate aligned well with the plan from Day 0 to Day 17. Digestate wasting did not start until the digester volume was filled up as scheduled in Figure 1b.
During Phase 2, the three digesters maintained their respective maximum feed rates until reaching the designed daily feed volume, that is 6.7% of the digester working volume which is equivalent to a 15-day SRT. However, the actual feed rates started to be approximately 5 to 10% lower than the planned values due to a reduction in the VS content in the THP-processed sludge. This lower VS content in this batch of sludge was attributed to a lower TPS:WAS blending ratio produced by Arlington WPCP. The drop in actual feed rates between Day 59 and 76 was another example of changes in feed sludge characteristics (Figure 2a). After Day 76, the actual feed rate once again aligned well with the designed plan. As shown in Figure 2b, the digesters with designed maximum feed rates of 0.31, 0.33, and 0.38 lb COD/lb VS/day successfully achieved the 15-day SRT on Days 34, 53, and 80, respectively, without any delay. The microbial concentrations in the digesters indicated by digester VS contents showed steady buildup and well alignment with the designed plan in general (Figure 2c).
During Phase 3, all three digesters maintained the 15-day SRT until reaching steady state. The steady state was defined as the timeframe during which VSR, daily biogas production rate, and VFA concentration did not show statistical differences based on T-test results. Throughout, key digester stability indicators, including TS, VS, pH, VFA, alkalinity, biogas production rate, and biogas composition were closely monitored.
Conclusions
By increasing the maximum feed rate from 0.31 to 0.33 and 0.38 lb COD/lb VS/day, the time required to reach the target15-day SRT was significantly reduced from 80 to 53 and 34 days, respectively. Throughout the startup phases, digester stability indicators suggested that VFA accumulation has occurred during the first 16 days of the startup process; however, the digesters quickly acclimated and stabilized without any rescue or corrective measures, such as feeding pauses or alkalinity supplementation, even at the more aggressive feed rate. These findings suggest that THP-enhanced digesters can successfully withstand higher loading rates during startup, offering a practical strategy to expedite achieving full operational capacity in AD processes.

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

Presentation time

09:30:00

09:45:00

Session time

08:30:00

10:00:00

SessionInnovative THP Startup and Biosolids Finishing

Session locationMcCormick Place, Chicago, Illinois, USA

TopicBiosolids & Residuals

Author(s)

Li, Yitao, Strawn, Mary, Racey, Lisa, Haile, Fasil, Balchunas, Brian, Moline, Chris, Higgins, Matthew, Novak, John, Wang, Zhiwu

Author(s)Y. Li1, M. Strawn2, L. Racey2, F. Haile2, B. Balchunas3, C. Moline3, M. Higgins4, J. Novak1, Z. Wang1

Author affiliation(s)Virginia Tech1, Arlington County Water Pollution Control Bureau2, HDR Engineering Inc.3, Bucknell University4

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Sep 2025

DOI10.2175/193864718825160166

Volume / Issue

Content sourceWEFTEC

Word count17