Williams, Todd

Mr. Williams has a 40+year career in environmental engineering. Todd has supported dozens of biosolids and residuals management master plans in his career which include adaptive planning to manage emerging contaminants such as PFAS. Todd is an engineering graduate of Virginia Tech and previously served as the Chair of the Water Environment Federations Residuals and Biosolids Committee. Todd works out of Jacobs Charlotte, North Carolina office where he serves as Jacobs Global Principal for Residuals Resource Recovery and Biosolids Management.

Titles from this speaker

Biosolids Incineration in the Times of PFAS

Abstract

Introduction Biosolids management in North America is significantly focused on beneficial use. As reported by the National Biosolids Data Project 2018 (NBDP, 2018), in the United States (U.S.), approximately 5.8 million dry metric tons of biosolids was generated in 2018 by Publicly Owned Treatment Plants (Water Resource Recovery Facilities or WRRFs), of which 53% was beneficially used (see Figure 1). The biosolids comprising Class B, Class A and exceptional quality EPA 503 designations are primarily used for agricultural applications. PFAS and other contaminants of emerging concern in biosolids are an issue that could impact the future of beneficial use as we know it. With existing (Maine, Connecticut) and other states considering potential of land applications bans, Biosolids Managers are considering alternatives to remove PFAS from biosolids. To date, thermal treatment has been identified as a promising pathway for removing PFAS from biosolids. Research has indicated that thermal oxidation (incineration), pyrolysis and gasification show high potential for removing PFAS from the solids. Other technologies, such as hydrothermal liquefaction, deep well injection and supercritical water oxidation (SCWO) are also in the early stages of development. Thermal oxidation has demonstrated that PFAS is removed from the residual and ash (Winchell, 2024). On-going research is evaluating the fate of PFAS in the gaseous phase. Similarly, pyrolysis and gasification can produce a biochar free from measurable PFAS and on-going research is evaluating the fate of PFAS in the gaseous phase (Williams, 2023). The other emerging technologies are thought to destroy PFAS, but research is required to verify this. Thermal oxidation is an established technology with an estimated 80 facilities in operation. In the U.S., thermal oxidation has traditionally been used to process unstabilized solids, specifically as a disposal method, with a few facilities employing external energy recovery, e.g. to produce electricity. Pyrolysis and gasification are well established in other industries with large facilities that use relatively dry feedstocks with large throughputs. However, pyrolysis and gasification are emerging technologies for biosolids management, because of the relatively lower throughput capacities required and the unique physical and chemical characteristics of biosolids causing heat balance and material handling issues. There are a few vendors around the world that are developing systems right-sized for biosolids management. Development of emerging technologies can take 10 to 20 years to reach commercialization. While industry develops and commercializes these technologies, there is a potential gap that needs to be filled to provide alternatives for existing facilities that have invested in technologies to stabilize biosolids for beneficial uses. Thermal oxidation is one such developed technology that can be added to existing technologies to produce a safe end product. Methodology This paper will present three biosolids stabilization technology process trains based on existing case studies (See Figure 2 for an example) that include thermal oxidation and using heat and material balances, demonstrate process viability, as well as compare economics and environmental factors. Process trains (see Figures 3,4 and 5) will include: - Class B mesophilic anaerobic digestion (MAD), dewatering and thermal oxidation - Class B MAD using WAS only THP, dewatering and thermal oxidation - Class A advanced MAD using thermal hydrolysis upstream of AD, dewatering and thermal oxidation Each of the process trains include state-of-the-art fluidized bed (FB) technology with energy recovery and air pollution control equipment that will meet New Source Performance Standards. Economic factors will include capital investment, operating and maintenance costs and life cycle costs. Environmental factors will include Part 503 Regulations, Part 60, Subpart LLLL regulations and greenhouse gas (GHG) emissions. Discussion The discussion will focus on the thermal oxidation technology that is required for the Class B and Class A AD process trains (see Figures 6 and 7), with an emphasis of meeting MACT emission regulations, as well as the results of the heat and material balances. The impact of the energy requirements for adding thermal oxidation will be presented. AD and advanced AD provide the most energy efficient way of converting biomass into recoverable energy through biogas utilization. So, the addition of thermal oxidation will focus on autogenous operation with a dewatered cake that has reduced volatile solids content due to AD and advanced AD. The impact on GHG emissions the biosolids management alternatives by adding thermal oxidation compared to agricultural land application will be reviewed. Specifically, the generation of nitrous oxide (N2O) by FB technology will be discussed and operational methods to reduce emissions will be presented. Closing This paper will be useful to Biosolids Managers, Water Resource Recovery Facility Managers and Consulting Engineers in understanding the immediate future role that thermal oxidation can fill for utilities that operate anaerobic and advanced anaerobic digesters facilities in providing a beneficial end-use for biosolids if land application is not available.

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

SpeakerBurrowes, Peter

Presentation time

11:25:00

11:45:00

Session time

08:30:00

11:45:00

SessionSome Like It Hot - Diving into Incineration, Pyrolysis, and Gasification

Session number13

Session locationBaltimore Convention Center, Baltimore, Maryland, USA

TopicAdvanced Thermal Conversion, Biochar, Energy and Carbon Neutrality, Energy Conservation/Management, Energy recovery, Gasification, Greenhouse Gases, incineration, Intensification, Knowledge Transfer, PFAS, PFAS/Emerging Contaminants, pyrolysis, Regulatory Requirements, Thermal Processes

Author(s)

Burrowes, Peter, Bharambe, Gokul, Williams, Todd, Ahanmisi, Ohis

Author(s)P. Burrowes1, G. Bharambe 1,T. Williams 1, O. Ahanmisi1,

Author affiliation(s)Jacobs, 1

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date May 2025

DOI10.2175/193864718825159803

Volume / Issue

Content sourceResiduals and Biosolids Conference

Word count8

Description: Biosolids Master Planning in Tulsa, Oklahoma to Develop a Sustainable Biosolids...

Biosolids Master Planning in Tulsa, Oklahoma to Develop a Sustainable Biosolids Management Program

Abstract

Biosolids Master Planning in Tulsa, Oklahoma to Develop a Sustainable Biosolids Management Program The Regional Metropolitan Utility Authority (RMUA) is responsible for the plant infrastructure as well as the operation and maintenance of the 16 million gallon per day (MGD) capacity Haikey Creek Wastewater Treatment Plant (HCWWTP) in Tulsa, Oklahoma. To evaluate the future needs for treating and handling biosolids generated at the HCWWTP, the RMUA authorized engineering development of a biosolids improvements facility plan and concept level design of needed facility upgrades. For the past 19 years, unstabilized biological sludge from the aeration process has been thickened and then hauled to the Tulsa Southside WWTP for treatment via anaerobic digestion and land application. However, this practice requires hauling of 9-10 tanker trucks a day to the City of Tulsa's Southside WWTP and requires significant coordination between the two plants. The goals of this study were to identify existing conditions, estimate future loadings (up to 24 MGD) , and evaluate cost-effective alternatives to upgrade the HCWWTP to a stand-alone facility, produce biosolids product that could be beneficially used, and define a solution that is not only within the RMUA budget constraints, but defensible (with no regrets) to RMUA and its two partner agencies, the Tulsa Municipal Utility Authority (TMUA) and Broken Arrow Municipal Authority (BAMA). The study provided an opportunity to not only investigate technologies for producing Class B or Class A biosolids for beneficial use, but also to consider adaptability to changing regulations and potential energy savings and reductions in carbon emissions. The following outlines the steps which were used to develop an updated solids management plan and concept level design for RMUA. 1.Existing and Future Conditions - This task included an evaluation of existing solids handling processes at the HCWWTP and the ability of the existing facilities to meet future projected loadings. Estimates of future quantities of solids production were made to determine appropriate sizing of solids management equipment in the near term (next 5 years) and into the future (20 years). This analysis was used to develop appropriate sizing criteria for all solids handling system components such that any deficits in capacity needs and the timing of equipment upgrades to eliminate those deficits were identified for future planning tasks. 2.Evaluation Criteria Development and Identification of Appropriate Technology Solutions -Through a workshop discussion with RMUA staff, the universe of technology alternatives was discussed with the goal of identifying potential biosolids management solutions and appropriate evaluation criteria consistent with RMUA goals and objectives were established. These criteria and potential technology options were defined in a workshop with RMUA stakeholders as well as engineering subject matter experts and the relative importance of these criteria determined. Fifteen biosolids management options as compared to the status quo were then identified in a collaborative process for consideration by the stakeholder team. The evaluation criteria previously developed was then applied against the potential technology solutions aimed at meeting RMUA goals. Figure 1 shows the result of the weighted scoring of these alternatives. At the conclusion of this criteria development and technology options identification, six potentially viable alternatives were selected by RMUA for further evaluation compared to status quo including: - Chemical-Thermal Hydrolysis - Mesophilic Anaerobic Digestion - Composting - Thermal Drying - Mesophilic Anaerobic Digestion plus Thermal Drying - Mesophilic Anaerobic Digestion, Thermal Drying plus Pyrolysis 3.Plant Simulation Evaluations - Existing whole plant simulation models for the HCWWTP were modified to analyze and evaluate the 7 alternatives identified to determine overall impacts on process performance, energy recovery and use of existing assets (tankages and equipment). Outputs of the simulations included overall energy balances, green-house gas emissions, and process performance compared to status quo. The outputs of this modeling exercise were then presented in a workshop with RMUA staff and used to further define the short-listed alternatives for further investigation and refinement. 4.Cost Evaluations - The simulation models formed the basis for conducting capital, O&M and life-cycle cost analysis of the 8 short-listed alternatives identified. Comparative cost evaluations were developed including vendor quotes for large equipment and cost estimating data from previous engineering project experience. Cost estimating tools were then used to compare capital, O&M and life-cycle costs for each alternative. These costs were then considered alongside the non-monetary evaluation criteria identified to develop a cost-benefit analysis. Figures 2&3 show the results of these cost and cost-benefit analyses. An interactive workshop was then held with RMUA stakeholders to fully vet the alternatives and determine three potential technology options for implementation. 5.Site Visits - The RMUA stakeholders then toured three representative technologies in Oklahoma including anaerobic digestion, thermal drying and composting. At the conclusion of the site visits, RMUA stakeholders agreed that while all three technologies could work for them, composting was the best choice due to simplicity of the process and production of a marketable product. 6.Implementation Planning - Implementation of the composting alternative was defined in terms of phasing, scheduling and budget planning to ensure the design and building of composting dewatering and composting facilities with the right capacity will be developed at the right time to meet the City's near-term and long-term needs. Through their engineering partner, City of Tulsa was able to apply for and secure grant funding from the USDA for 20 percent or$ 9.8 million of the total project cost (estimated at $48 million). Project Status One of the most interesting aspects of the project was that based on the previous biosolids management study done in 2014, preconceived solutions of anaerobic digestion and improved dewatering to then land apply biosolids cake was thought to be the solution that would be recommended. However, by revisiting potential solution options and redefining what criteria were most important, several different solutions were reconsidered. Ultimately, site visits conducted by RMUA Staff proved to be extremely helpful in the selection of the composting process that is proven, simple to operate and produces a biosolids product with multiple uses. This selection really paid off when grant funding became available that the compost production process proved to be qualified for, saving the RMUA nearly $10M in costs. This part of the story will be detailed in the paper and presentation. The Haikey Creek Wastewater Treatment Plant Biosolids Improvements Project has been approved and is in the design phase of a 10.2 dry ton per day capacity aerated static pile composting facility expandable to 15.3 dry tons per day in 2060. Major facility components include gravity thickener improvements, sludge storage, new centrifuge dewatering as well as a new covered aerated static pile facility. This case study will present details and results of the entire planning process which will provide planners, engineers, administrators, and owners with insight into the planning process used to select the right solution using specific owner driven criteria as well as costs to choose the right solution for their biosolids management needs.

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

SpeakerWilliams, Todd

Presentation time

08:30:00

09:00:00

Session time

08:30:00

11:15:00

SessionCase Studies & Lessons Learned

Session number27

Session locationOklahoma City Convention Center, Oklahoma City, Oklahoma

TopicCompost, Master Planning, Residuals

Author(s)

Williams, Todd

Author(s)T. Williams1, A. Romero1, T. Johnson1, L. Ostervold2, M. Vaughan3

Author affiliation(s)Jacobs 1; Jacobs 1; Jacobs 1; Black & Veatch 2; City of Tulsa 3;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Jun 2024

DOI10.2175/193864718825159427

Volume / Issue

Content sourceResiduals and Biosolids Conference

Word count14

Impact of Several Biosolids Stabilization Technologies on PFAS

Abstract

Abstract Summary It is well understood that conventional treatment approaches do not effectively remove PFAS from liquids or solids streams at wastewater treatment plants. Future regulatory enforcement of PFAS has varied state-to-state providing uncertainty for utilities as they plan for future process upgrades. To assist utilities and biosolids producers, several biosolids products were tested including dried biosolids, pyrolyzed dried biosolids and composts, all produced with non-industrially impacted biosolids to assess the concentration of PFAS compounds in the finished products and the ability of these processes to reduce and or remove PFAS compounds. The full paper will summarize findings from this study. Introduction Per- and Poly-Fluoroalkyl Substances (PFAS) are a large family of organic compounds, including more than 4,500 synthetic fluorinated organic chemicals used in commercial, consumer and industrial products since the 1940s. Conventional treatment methods do not efficiently remove PFAS which are resilient to degradation and tend to sequester to the treated solids produced and the resultant biosolids. In its most recent (2021) review of pollutants in biosolids, the US EPA identified eight PFAS in biosolids, and is undergoing a problem formulation process which will serve as the basis for determining whether regulation of PFOA and PFOS in biosolids is appropriate. If EPA determines that a regulation is appropriate (currently expected in 2024), biosolids producers will be required to meet certain standards. This potential outcome of EPA's review underscores the importance of understanding technical solutions available to treat PFAS in biosolids if required based on EPA's review process. Technical Content To assist utilities and biosolids producers to understand options available to them to mitigate potential PFAS contamination in biosolids, several biosolids products were tested including dried biosolids, pyrolyzed dried biosolids and composts, all produced with non-industrially impacted biosolids to assess the concentration of PFAS compounds in the finished products and the ability of these processes to reduce and or remove PFAS compounds. Samples of input and output solids, bulking agents and finished products were analyzed for 24 PFAS compounds utilizing Liquid Chromatography Tandem Mass Spectrometry (LC/MS/MS). The facilities tested include: three dried biosolids facilities, two pyrolyzed dried products including output solids, gas and oil, and six compost products. Figure 1 provides an overview of PFAS (PFOA, PFOS, and total PFAS) concentrations by sludge type and the impact of composting operations. This figure demonstrates the progression (and conversion) of the PFAS concentration from the various raw sludge types. In some cases, the type of bulking agent used (fresh yard waste, wood chips, or the amount of recycled bulking agent used) can impact the concentrations of various PFAS compounds in the final compost products. Depending on the sludge type, the composting process has shown to increase or decrease measured PFAS. The variability in the results suggest the presence of precursors in the raw sludge. Additional detail regarding these impacts will be provided in the full paper. Figure 2 summarizes reduction of PFAS compounds through thermal drying using a rotary kiln dryer, where a range of 25-75% reduction was observed (45% average reduction) through drying. Figures 3 and 4 summarize the impact of pyrolysis on PFAS degradation in undigested digested and digested sludges, respectively. In both cases, a significant reduction in PFAS compounds was observed through pyrolysis, with near non-detect PFAS concentrations in the biochar and between 85% and over 99% reduction of measurable PFAS was achieved on a mass basis of all outputs including biochar, biooil and pyrogas. This will be one of the first published results on the entire outputs from the pyrolysis of wastewater sludges. Paper and Presentation This paper and presentation will provide information regarding the measured concentrations of PFAS in wastewater solids, dried biosolids, pyrolyzed biosolids (including the resultant pygas) and biosolids based compost products. PFAS precursor analyte presence and concentrations in the input solids as well as the wastewater treatment process used to generate these products will also be presented. This information will be useful for those considering methods to reduce or eliminate PFAS in their own wastewater solids or other input wastewater solids at existing or planned biosolids management operations to ensure the lowest feasible PFAS concentrations in end products can be achieved. This presentation will help utility planners, operators, engineers, and administrators understand the nature of the PFAS issue in biosolids, how these compounds are introduced into biosolids, the rapidly changing regulatory landscape, and what technologies are being used to reduce or eliminate these compounds from wastewater biosolids products.

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

SpeakerWilliams, Todd

Presentation time

9:30:00

10:00:00

Session time

8:30:00

11:45:00

SessionSession 10: PFAS Challenges and Treatment

Session number10

Session locationCharlotte Convention Center, Charlotte, North Carolina, USA

TopicEmerging Issues (PFAS, Microplastics, Covid, etc.)

Author(s)

T. Williams

Author(s)T. Williams1, S. Grieco2, B. Bani3, 4,

Author affiliation(s)Jacobs1

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date May 2023

DOI10.2175/193864718825158798

Volume / Issue

Content sourceResiduals and Biosolids

Word count9

Description: Removal and Transformation of PFAS from Biosolids in a High Temperature Pyrolysis...

Removal and Transformation of PFAS from Biosolids in a High Temperature Pyrolysis System - A Bench Scale Evaluation

Abstract

Per- and Poly-Fluoroalkyl Substances (PFAS) are a large family of organic compounds, including more than 4,000 synthetic fluorinated organic chemicals used since the 1940s. PFAS have unique surfactant properties that make them repel both water and oil. Because of these properties, they have been used extensively in firefighting foams, surface coatings, and protectant formulations for consumer products, including paper and cardboard packaging products, carpets, leather products and clothing, construction materials, and nonstick coatings (ITRC, 2020). Manufacturers of these items often discharge to Water Resource Recovery Facilities (WRRFs). Landfill leachate discharge and household sewage are also common sources of PFAS in WRRF influent. Conventional WRRFs have proven to be relatively ineffective in removal of PFAS and discharge from WRRF is considered a major source of PFAS in the environment (Ahrens 2011, Chen et al., 2018). There is mounting evidence that continued exposure above specific levels of certain PFAS may lead to adverse health effects (USEPA 2016a, 2016b, ATSDR 2018a). PFAS concentrations in wastewater and sludge or biosolids are mass loading based. Long chain PFAS compounds discharged into WRRFs partition to the solids and end up in the resulting sludge or biosolids. The presence of PFAS in WRRF biosolids has raised a concern in the recent years for beneficial land application programs as PFAS could mobilize in soil, leach into run-off, infiltrate into groundwater or be taken up by biota (Lindstrom et al. 2011, Rich et al. 2015, Sepulvado et al. 2011). Within the PFAS family of compounds, perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) are the two most common compounds and are a focus of Federal and State drinking water and environmental regulations. These compounds were commonly used in the manufacture of aqueous film forming foams (AFFF) for fighting aircraft fuel fires and other industrial and commercial products. In February 2019, the US EPA developed an action plan to limit human exposure to potentially harmful levels of PFAS in the environment. The short-term action plan includes testing for measurable PFAS and PFAS precursors in biosolids. The action plan was updated in February 2020 indicating that EPA is developing a risk assessment to better understand the potential public health and ecological risks associated specifically with PFOA and PFOS in land-applied biosolids. With mounting concern about the presence of PFAS in biosolids and the lack of specific guidance from the US EPA regarding the risks of these compounds within biosolids, some states have begun their own evaluations on this topic with suggested concentration limits of PFAS in biosolids used for land application. However, state regulatory agencies do not have a consistent approach to managing PFAS in biosolids. These concerns coupled with lack of consistent guidelines from the US EPA and state regulators has caused utilities to consider alternatives to eliminate the presence of PFAS in biosolids to minimize their risk exposure to potential future regulatory standards. As a result, technologies which can effectively destroy PFAS in biosolids based products are being investigated. One such technology is pyrolysis. Pyrolysis is the conversion or cracking of biomass or biosolids at high temperatures in the absence of oxygen. As most organics are thermally unstable, they can be split in a pyrolysis process by a combination of thermal cracking and condensation reactions into gaseous (pyrogas), liquid (bio-oil), and solid (biochar) fractions. With limited research available on the ability of pyrolysis to eliminate PFAS from biosolids and the fate of PFAS in the resulting effluents (solids, liquid, and air), there is a need to provide actual data for engineers and planners to evaluate as to the actual performance of the pyrolysis process with respect to PFAS reduction and fate. Jacobs and CharTech Solutions (CharTech) recently partnered to investigate the application of CharTech's High Temperature Pyrolysis Technology for biosolids management, and its efficacy in eliminating PFAS from the solid fraction. In addition, the transformation or elimination of PFAS compounds by measuring concentrations in the resultant bio-oil and pyrogas produced from the pyrolysis process were evaluated. This is one of the first analyses done using dried biosolids which captured PFAS data from the all output matrices including the resultant char, bio-oil and pyrogas fractions resulting from the pyrolysis of biosolids. Bench scale testing was performed in a continuously fed pyrolysis unit to compare the PFAS removal performance at 500 °C and 700 °C pyrolysis temperatures. Dried biosolids tested in the bench scale test were derived from un-stabilized waste activated sludge produced from two WRRFs operated by Jacobs. The solids were previously dewatered with belt filter presses to approximately 20 percent solids and subsequently dried in a batch thermal dryer fired with natural gas to evaporate water, resulting in a biosolids product that was approximately 93 percent solids. The dried biosolids material previously met Class A Exceptional Quality biosolids product status by achieving all pathogen and vector-attraction reduction requirements, as well as meeting the concentration limits of heavy metals according to the U.S. Environmental Protection Agency's (EPA) 40 Code of Federal Regulations (CFR) Part 503 Rule. Twenty eight of the most commonly measured PFAS compounds were analyzed in the feed biosolids, biochar, bio-oil and 31 PFAS compounds were analyzed in the pyrogas. Only six PFAS compounds (10:2 Fluorotelomer sulfonic acid, PFOS, N-Et PFO sulfonamidoacetic acid, N-Me PFO sulfonamidoacetic acid, Perfluorohexanoic acid, and Perfluoroundecanoic acid) were measured above the detection limits in the feed biosolids. Three PFAS compounds were detected in the biochar at the 500 °C pyrolysis temperature (Perfluorohexane sulfonic acid, Perfluorohexanoic acid, Perfluorooctanoic acid), all at less than 0.5 ppb (dry weight). No PFAS compounds were detected in biochar at the 700 °C pyrolysis temperature. PFOS was measured at 26.6 ppb in the feed biosolids but not detected in the biochar, bio-oil or pyrogas at either pyrolysis temperature. Although not detected in the dried biosolids, PFOA was detected at very low concentrations in biochar and pyrogas indicating a lack of complete destruction and/or transformation of precursor compounds during pyrolysis. Higher concentration of Perfluorohexanoic acid (PFHxA) in pyrogas at 500 °C compared to 700 °C was observed, suggesting greater destruction of PFHxA at a higher temperature. To better understand the PFAS fate through the pyrolysis process, mass balance analysis on biochar, bio-oil and pyrogas streams were conducted and removals of PFAS were estimated. The result of mass balance analysis indicated a total measured PFAS mass removal of 84.4% and 95.6% for 500 °C and 700 °C, respectively for all the PFAS tested in this study. This paper will describe in detail the testing apparatus and procedures used and provide a full description of the results measured. The information will be useful for engineers, planners, scientists, utilities, regulators and others interested in the evaluation of pyrolysis as a potential biosolids management alternative to minimize PFAS in biosolids.

The following conference paper was presented at Residuals and Biosolids 2021: A Virtual Event, May 11-13, 2021.

SpeakerWilliams, Todd

Presentation time

13:40:00

14:00:00

Session time

13:00:00

14:00:00

SessionPFAS and Contaminants of Concern in Biosolids

Session number1

Session locationSimu-Live

TopicBiosolids, Microconstituents, pyrolysis

Author(s)

T. WilliamsS. GriecoB. BaniA. FriedenthalA. White

Author(s)T. Williams1; S. Grieco2; B. Bani3; A. Friedenthal4; A. White5

Author affiliation(s)Jacobs 1; Jacobs 2; Jacobs 3; Char Technologies 4; CharTech Solutions 5;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date May 2021

DOI10.2175/193864718825157943

Volume / Issue

Content sourceResiduals and Biosolids Conference

Word count19

Description: Transforming THP Cake into Soil and Halving the Tonnage Using the New Dune Aerated...

Transforming THP Cake into Soil and Halving the Tonnage Using the New Dune Aerated Static Pile Process

Abstract

Utilization of the Thermal Hydrolysis Process (THP) to treat sludge before anaerobic digestion has been practiced since 1995. There are many benefits to this process including improved digestion performance, the ability to feed digesters at a higher solids concentration thereby reducing needed digestion volume by 50% or more, a reduction in the quantity of solids remaining after digestion, improved dewatering, and production of a low odor Class A exceptional quality (EQ) biosolids cake product (Barber, 2020). There are now more than 70 full scale THP plants worldwide that utilize this process including several in the US with more in development. One of the challenges that yet remains with this process is that even though a low odor Class A EQ biosolids is produced, the dewatered cake at 30% solids still looks like Class B biosolids cake and must still be land applied on agricultural farmland. Work has been done using simple windrowing to air dry thermally hydrolyzed biosolids to approximately 55-60% solids to produce a more soil-like material (Brower et.al., 2018). The air-dried biosolids product can then be more readily used in landscaping and horticulture applications. However, the windrow air drying process can take 3-6 weeks or longer, requires a significant amounts of land area, regular turning of the windrows to achieve the necessary level of drying, and includes risk of odor concerns. In locations with significant precipitation, this area must be covered to prevent reintroduction of moisture into the material. A simplified process has been developed called Dune that takes advantage of the natural biological process to generate heat and to achieve drying of THP dewatered cake to 55-60% solids in less than 2 weeks (Figures 1 and 2). This process requires only a fraction of the space (approximately one third) required by windrow air drying while significantly reducing ammonia and odor emissions. The Dune process has been successfully demonstrated at field scale at two THP solids processing facilities: one in the US and one in the UK (Figures 3 and 4). The process uses a portion of previously biologically dried THP cake blended with fresh wet THP cake to produce a mixture that has adequate porosity and bulk density to allow for forced ventilation in an aerated static pile configuration. Results of these field scale trials prove that sufficient energy remains within the dewatered THP cake to continue biological degradation with naturally occurring aerobic microorganisms present within the recycled dried THP cake. No external amendments are required. A major by-product of this continued biological degradation process is heat. By providing aeration to maintain aerobic conditions within the mass of the mixed materials, temperatures rapidly rise, and moisture is removed. The result is that the tonnage of the solids can be reduced by 50% which in turn will reduce costs of hauling and land application by 50% or more. In addition, the characteristics of the dried product are like a well stabilized compost or soil that can be utilized in horticultural applications such as landscaping, turf, and ornamental gardens instead of only agricultural farmland (Table 1). The product pH transitioned from slightly basic to just below neutral, the carbon dioxide respiration rate significantly reduced indicating more stability, and a slight decrease in volatile solids occurred showing further volatile solids reduction. These changes in the biosolids characteristics while maintaining Class A biosolids status allows for multiple uses instead of only in agriculture, thus opening different product markets. Another benefit of the process is that by changing the conditions of the biosolids from anaerobic to aerobic, methane emissions from the stockpile of material are almost immediately stopped. Emissions testing of the process demonstrated a drastic reduction in methane emissions (Figure 5) and potential GHG reductions when compared to conventional storage of dewatered THP cake prior to land application. This presentation will provide a description of the Dune process and discuss results of the field scale demonstrations including the impact on product quality, product quantity, and methane emissions as compared to the conventional method of storing THP biosolids cake. O&M cost comparisons will also be provided showing the cost-benefit of full-scale application of the Dune process to Class A THP cake.

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

SpeakerWilliams, Todd

Presentation time

10:45:00

11:05:00

Session time

10:45:00

11:45:00

SessionExploring Pathways to Dried Biosolids

Session number3

Session locationBaltimore Convention Center, Baltimore, Maryland, USA