Browse

Introduction Microplastics (MPs) are plastic debris resulting from plastic waste fragmentation or direct emissions of micro- and nano-sized plastics from a variety of sources. Recently, MPs were added to the list of global threats because they are ubiquitous and may pose a risk to the food chain as a result of their interaction with organic contaminants (OCs) and heavy metals (Y. Wang et al., 2022; Zhou et al., 2022). Hence, understanding the interaction mechanisms of OCs with MPs is essential for evaluating the impact of MPs on the environment. Wastewater treatment plants receive a high quantity of MPs from a variety of sources. These MPs accumulate in sludge and this, together with the sorption potential for OCs, some of them endocrine disruptors (EDCs), on MPs cause a special concern for land application of biosolids. Furthermore, MPs also undergo aging in treatment processes and in environment, which may in turn affect their interaction with OCs. MPs subjected to UV aging have been widely studied in the literature, however, their biological aging of them are not equally investigated (Zafar et al., 2022). Especially bioaging during sludge digestion which is applied right before land application was not investigated. Additionally studies indicated that MPs not only simply bio-age during digestion but also inhibit the microbial community and may lower methane production levels when present in high doses which also creates additional concern for the environment as the doses of MPs keep increasing (Wei et al., 2019). This study aims to investigate the bioaging potential of polyethylene (PE) MPs in mesophilic anaerobic digesters operated as BMP reactors. Study also examines the comparative sorption of two OCs, one of them an EDC, on pristine (PE0) and bio-aged polyethylene (PE1) collected from anaerobic digesters. For this purpose, biotic and abiotic anaerobic reactors (BMP test bottles) containing a high dose of PE MPs (200 mg/g TS) were operated together with reactors containing no MPs. Following digestion bio-aged and pristine MPs are characterized using FTIR and SEM to compare the changes in PE's physical and chemical properties. Sorption of two OCs, namely 2,3,6-trichlorophenol and triclosan (an EDC) are investigated. Methane production is monitored in biotic and abiotic reactors to see the effect of MPs on digestion process to check whether there is inhibition on the microbial community. Materials and Methods Three sets of reactors were designed: biotic (B), abiotic (A), and seed control (S). BMP reactors were set-up using waste activated sludge (WAS) and digested sludge (seed) collected from a conventional WWTP with a capacity of 765,000 m3/d (4 millon design population equivalent). In reactors F/M ratio was 1, TS was adjusted to 2% and VS/TS ratio was 0.59. Details of reactor sets including the number of replicates are explained in Table 1. Biogas volumes in reactors were measured using a water displacement set-up. A gas chromatography (GC) device equipped with a thermal conductivity detector (TCD) was used to measure the biogas methane content. When the reactors are terminated full analysis of parameters shown in Table 2 will be conducted. PE used in reactors had particle size range of 425-500 µm; which were sieved, washed, and ultrasonicated before added to the reactors. The initial characteristics of PE were such that the density was 0.935 g/cm3, the crystallinity (by DSC) was 49.4% and melting temperature (Tm) was 126 °C. Sorption tests with pristine PE (PE0) showed a maximum sorption capacity of 1.0 mg/g for 2,3,6-trichlorophenol (TCP) and 6.9 mg/g for triclosan (TCS). Bioaging may affect sorption onto MPs favorably or unfavorably, depending on the type of changes that happen on PE (e.g., oxidation, peeling, etc.) affecting sorption mechanisms. Results and Discussion Table 2 demonstrates the initial reactor characteristics. The initial VS/TS ratio is higher for biotic and abiotic reactors, on the other hand it is lower in seed control, indicating that seed is more stable as expected. pH values of the samples are as expected as well; with seed having a little higher pH due to being digested compared to the sample. The COD value in abiotic reactors showed to have a wider range and higher values than any other set due to the effect of HgCl2, added to suppress the microorganisms and inhibit biotic activity. On the other hand, seed control showed the lowest COD content because it is stable and there is no WAS in the reactor so total organic content is almost half of the other reactors. The cumulative biogas volume was measured for 45 days (data not shown). Biotic reactors with no MPs addition showed higher biogas production than those with MPs, which, could be due to inhibition caused by high quantity of MPs. Reactors kept producing biogas but at lower amounts as time went on. Seed control reactors produced much smaller amount of biogas. Figure 1 shows the cumulative methane production in mL up to 45 days. Corresponding to increasing biogas volume, methane content also increased within all the biotic reactors. Similar to biogas production, methane production slowed down with time. B0 reactors showed the highest amount of methane, suggesting inhibition effect of MPs. S0 reactors produced much smaller amount of methane since they already reached a stable state before reactor set-up. Abiotic reactors produced no gas, with some days having negligibly small amount of gas production. Interestingly, in the reactors that contain MPs, although methane volume, parallel to the biogas volume, was less than those that did not contain MPs, the percent methane in the biogas was not necessarily less. With our experience we know that biogas and methane production decrease as the organic content in sludge is consumed; which corresponds to a time long before 60 days. Operating reactors for 60 days is with the expectation that 60 days is long enough to see some effect of bio-aging on the plastics. At the reactor termination, full characterization of the reactors will be done. MPs will be manually sieved and picked up from sludge then washed and left to dry. In an earlier trial to analyse the recovery of MPs from the sludge samples, it was found that 84% recovery by wt was achieved with MPs in the size range used here. Recovered MPs will be used for further analysis where, a sample of the abiotic-aged and biotic-aged MPs will be sent to FTIR analysis and SEM imaging. At the same time sorption tests will be conducted on the obtained MPs, for sorption potential of TCP and TCS as model OCs. Based on the level of aging and preliminary results, new reactors will be set for further studies. Results of sorption studies with bio-aged MPs will be included in the full-text manuscript. Conclusion Presence of PE in the digesters affected biogas production negatively, showing discernible difference when compared to the control reactors. Interestingly, in the reactors that contain MPs, although methane volume, in parallel with the biogas volume, was less than those that did not contain MPs, the percent methane in the biogas was not necessarily less. Experimental results currently indicate that the biogas volume in biotic reactors started decreasing each day, demonstrating that sludge is stabilized and the experiment is coming to an end. Once the reactors are taken down, the plastics will be isolated from the reactor content, examined for bio-aging and will be used for sorption of TCP and TCS. Acknowledgements This study was supported by TUBITAK Project No: 220N044.

Summary This paper will present the results of collaborative inter-agency feasibility assessment for a regional program to manage residuals and biosolids for several public sector utilities in the South Carolina Low Country. The collaboration has been completed in multiple phases. The first phase (Phase I) involved six (6) public service agencies and covered ten (10) treatment plants representing the largest utility service providers in the South Carolina Low Country. The second phase (Phase II) involved four (4) agencies and six (6) treatment plants after two of the agencies exercised an 'off-ramp' option. The third phase (Phase III) involved three (3) agencies forming a new public agency authority the Charleston Regional Resource Recovery Authority (CRRRA) to manage a regional composting facility to be delivered under a progressive design-build-operate model. Background Most major wastewater treatment service providers in the Charleston, Berkeley, and Dorchester (CBD) counties currently dewater unstabilized wastewater treatment residuals and send the dewatered cake to either the Waste Management Oakridge Landfill or Berkeley County Landfill. Prior to the current practice of landfill disposal, many of these utilities had relied upon third-party end-users, such as GenEarth and Williamsburg Composting, to receive and process their solids. However, due to odor and operational concerns, these third-party operated facilities were unexpectedly decommissioned, leaving the utilities dependent upon the landfills for disposal of their solids. Recent landfill slope stability failures at landfill facilities in Georgia, believed to be caused by receipt and handling of excessive wet waste (e.g, dewatered sewage sludges), have caused regional landfill operators in both Georgia and the Carolinas to examine the ratio of wet waste (WW) to municipal solids waste (MSW) and explore options to reduce the WW:MSW ratio. As a result, the Oakridge and Berkeley County landfills have assessed utilities sending wet waste increased tipping fees for additional material handling and management costs at the landfill facilities. These increasing tipping fees, combined with other operational considerations, have been a primary driver for utilities to seek alternative residuals management approaches. As a result of the uncertainty the future might hold the utilities in the CBD region, representing six (6) organizational entities and ten (10) treatment facilities, formed a consortium to collaborate and explore regional alternatives for a collaborative biosolids management program: Phase I Initial Planning Assessment The Phase I feasibility assessment consisted primarily of the following major activities: -Estimates of Current (CY2020) and Future (CY 2050) Flows, Loads and Solids Quantity Estimates -Characterization and Quality of Dewatered Sludge Quality Factors -Regulatory Review and Benchmarking Assessment -Market Assessment for Residual and Biosolids Products in South Carolina -Alternative Development and Assessment Of particular interest in Phase I is the 'Alternative Development and Assessment' work where the following major approaches were assessed: -Thermal Hydrolysis and Mesophilic Digestion (THP+MAD) Class A Dewatered Cake End Product -THP+MAD with Thermal Drying Class A Dried Product -Fluid Bed Thermal Oxidation Ash End Product Preliminary system sizing was completed for each of the three alternatives examined and an AACE Class 5 level cost estimate developed for capital cost (CAPEX) for each facility. Operating costs were developed for each alternative and utilized, in combination with project flow loading rates, to develop lifecycle operating costs (OPEX) on a 20-year basis. Total lifecycle costs (TLCC), a combination of the CAPEX and OPEX, were developed for each alternative. Based on TLCC each of the alternatives had a similar expected cost with trade-off between higher CAPEX to achieve lower OPEX. Given similarity in TLCC for the alternatives the team used a multi-criteria assessment tool (CONVERGE) to assess both the cost and non-cost factors such as: -CAPEX -OPEX -Operability and Complexity -Maintainability and Complexity -Regulatory Compatibility -Environmental Stewardship -Long-Term Sustainability -Final Product Marketability The multi-criteria decision-making process from Phase I will be described in the results presented in the paper and presentation. Phase II Continuing Collaboration Development After the completion of the Phase I Feasibility Assessment, four (4) of the six (6) utilities in the consortium decided to continue efforts to further define a regional solution and develop a consortium-owned facility master plan. The Phase II efforts consisted of the following major activities: -Update the mass balance for the Phase I selected management alternatives for the reduced loading from the four (4) remaining utilities -Develop revised conceptual layout and process flow diagrams -Develop updated CAPEX, and OPEX cost estimates -Consider site location requirements for property assessment and acquisition -Consider the potential for addition of gasification or pyrolysis (post-dryer) for PFAS destruction -Develop a phased approach to facility build-out incorporating thermal drying as the first phase -Solicit interest of third-party owned and operated contract service providers to provide residuals management services via a public-private partnership (P3). This portion of the paper and presentation will describe the updated management approaches and the results of the solicitation of third-party owned and operated approaches for residuals management. As a result of this solicitation the utility partners decided to further consider development of a public-private partnership in the Phase III work. Phase III Formation of a Joint Authority and Solicitation for Facility Design-Construction-Operation Following completion of the Phase II work one utility partner withdrew from the collaborative and the three (3) remaining utility partners progressed into Phase III. Phase III included further evaluation of the third-party management approaches solicited in the Phase II work and consideration of composting as a viable management approach to produce a Class A stabilized material that would not have to be routed to a landfill for management. Phase III also included the formation of a separate legal entity, the Charleston Regional Resource Recovery Authority (CRRRA), that is jointly controlled by the three remaining utility agencies. The purpose of the CRRRA is to provide an entity to develop and operate a regional residuals management facility that will utilize Class A biosolids composting to stabilize and treat dewatered residuals from each of the agencies treatment facilities. Currently CRRRA is in the process of submitting proposals from entities that would be able to deliver under a progressive-design build-operate model a regional composting facility with a processing capacity of 100,000 tons per year. The facility will be owned by the CRRRA following the design-build phase work and will have an ongoing operating services contract for the receipt and processing of dewater residuals. Proposals are due in the middle of December 2022 with plans to evaluate and award in the first quarter of 2023. This portion of the paper and presentation will share the background behind the formation of the CRRRA including discussion of the legal formation of the authority and the governance structure of the jointly controlled agency. This portion of the paper will also share the process utilized for the solicitation of proposals from interested parties for the design-build-operate Class A composting facility including scoring and evaluation criteria utilized in the selection.

INTRODUCTION Arlington County (County) is implementing new biosolids management facilities at the Arlington County Water Pollution Control Plant (WPCP). The Arlington County WPCP Re-Gen Program (Program) is a comprehensive program that will include the engineering, design, construction, maintenance, startup, and operation necessary to add sustainable equipment and systems to effectively recover the County's renewable resources, produce a Class A biosolids product, and most efficiently utilize the biogas. The Program includes upgrades or replacement of nearly all existing solids handling processes. A thermal hydrolysis process (THP) followed by anaerobic digestion (AD) form the backbone of the new treatment train. The overall process flow diagram for the Facilities is shown in Figure 1. PURPOSE AND SCOPE OF STUDY The purpose of the biogas utilization evaluation is to review all feasible alternatives for the beneficial use of the biogas to assist in meeting the County's sustainability goals while also meeting the energy needs of the WPCP and then perform monetary, non-monetary, and sustainability evaluations to determine the recommended alternative for the County. It is not a stated goal of the Program to be 'cash positive' many additional factors impact the overall Program cost. The scope of the analysis included only biogas utilization portion of the Program, and not any other of the solids handling components. ALTERNATIVES DEVELOPMENT There are several options for the beneficial use of the biogas produced in AD, each with its own advantages and disadvantages including biogas conditioning requirements, capital cost, O&M requirements, financial benefits, sustainability impacts, and GHG emissions. From the potential biogas uses the following six major alternatives were developed: Alternative 1: Process and building heating Alternative 2A: CHP with Engines Alternative 2B: CHP with Turbine Alternative 3A: RNG to Pipeline Alternative 3B: RNG as CNG Alternative 4A: RNG and CHP with Engines Alternative 4B: RNG and CHP with Turbines For each of the alternatives, an energy balance was developed to help illustrate the sources and flows of energy purchased and produced. The resulting diagrams show the process and building heating requirements, electrical power requirements and production, equipment efficiencies, NG purchase, and biogas flaring for each alternative. These energy balances formed the basis for the financial, non-financial and sustainability analysis performed. FINANCIAL ANALYSIS A financial analysis focused on the financial costs over a 6-year period of construction and 25-year period of subsequent operations. Figure 2 presents the original conceptual construction cost (inclusive of contractor overhead and profit [O&P], mobilization and other preliminary costs, and contingency), and total present value of all capital and net operating costs through 2052, assuming a 3 percent discount rate. The financial analysis indicates that although Alternatives 3A and 3B (RNG alternatives) do not have the lowest capital cost, they do have the lowest total present-value cost due to the anticipated value of the RNG. In comparison, Alternatives 4A and 4B (RNG and CHP alternatives) would entail larger capital costs and comparable present-value costs when compared to Alternatives 2A and 2B (CHP alternatives). The initial present-value financial analysis supports eliminating Alternatives 4A and 4B for further consideration because of high capital costs, high overall complexity, and comparable present financial values to Alternatives 2A and 2B. NON-FINANCIAL ANALYSIS To account for non-monetary factors that impact stakeholders a comprehensive non-financial analysis was completed. This analysis included the development of evaluation criteria, shown in Table 1, and then the subsequent weighting of the criteria and scoring each alternative for those criteria. The results of the non-financial analysis are shown in Figure 3. Alternative 3A had the highest (most favorable) non-financial score at 68.2, followed by Alternative 1 at 67.5. Alternative 2B had the lowest non-financial score of 57.6. The main differentiators between the RNG alternatives (Alternatives 3A/3B) and CHP alternatives (Alternatives 2A/2B) were that the RNG alternatives had: -Lower localized emissions -Reduced noise -Increased flexibility and reduced flaring -Lower maintenance complexity -Adaptability to future opportunities SUSTAINABILTY CRITERIA The sustainability, or environmental impact, of the alternatives was identified by using the anticipated reductions of GHG emissions (namely CO2) for each alternative and using a social cost of GHG approach to monetize the reductions. The net GHG change presented is solely for the biogas utilization equipment, not the entire Program. Table 2 presents net change in GHG emissions for each of the sources of energy for 2037. Overall, Alternatives 2A, 3A, and 3B have greater emissions reductions than Alternatives 1 and 2B. COMPOSITE RESULTS To complete the analysis and understand the ultimate best use of biogas for the program the financial results, non-financial scoring and GHG emissions reduction, are combined into plots to illustrate the composite results for each alternative. Figure 4 presents the composite results of the base case scenario. Four additional scenarios were developed to reflect the variability of RIN prices, electrical prices and the social cost of carbon. For this base scenario, without considering the social cost of carbon, Alternative 3A had the highest non-financial score and the second lowest present financial value. SENSITIVITY ANALYSIS Finally, a computationally rigorous sensitivity analysis, using Monte Carlo simulation methods, was completed to assess the combined impact of changing several factors at once. Table 3 presents the limits and estimated value for variables that are included in the Monte Carlo model. Separate probability distributions are formed for each of these factors and the sources for these distributions include HDR assumptions and existing data. The results from the Monte Carlo simulation are presented as a probability distribution of possible outcomes, given the range of possible inputs of uncertain parameters. Figure 5 shows the distributions of possible present values of total financial and social outcomes for all five alternatives, in both probability density function (PDF) and cumulative density function (CDF). The CDF has a useful interpretation for decision making because it can clearly indicate the probability that a condition holds, such as if total present value of benefits exceeds costs. Figure 5 shows that Alternatives 1, 2A and 2B all have a very narrow range of potential financial values, showing that costs exceed benefits for the modeled parameters. Alternatives 3A and 3B have a wide range of potential financial values, which is a function of the uncertainty in the RNG market. However, even with the wide range, a majority of the model runs indicate a negative financial value (i.e., benefits exceed costs for the modeled parameters) for the 3A and 3B gas utilization scenarios. CONCLUSIONS AND RECOMMENDATIONS Based on the analyses presented, the Water Pollution Control Bureau (WPCB) recommends proceeding with Alternative 3 (RNG) as the selected biogas utilization approach. The basis for this recommendation is as follows: -The RNG alternatives have the lowest net present value for the baseline conditions using conservative capital and operating costs. -Alternative 3A (RNG into pipeline) scored the highest in the County's non-financial scoring. The County found that the RNG alternatives would be less complex and result in fewer localized impacts than the CHP alternatives. -A sensitivity analysis concluded that when considering multiple variables, including RIN volatility and changes to electrical rates, Alternative 3A had a very high likelihood of being more financially advantageous than Alternative 2A. -The County has the ability to retain GHG credits if the biogas is used within Arlington County for transportation purposes. Should the biogas be used outside of Arlington County, the revenue from the RINs could be used to purchase an equivalent amount of GHG credits on the open market. -Benefits of on-site CHP are limited because the CHP size would not be sufficient to power the entire WPCP and the existing WPCP has adequate stand-by power. The County's current preference is for Alternative 3A (RNG into pipeline) over Alternative 3B (RNG as CNG) due to this option's diverse opportunities for end use customers, rather than relying on a specific direct customer. However, the final decision to inject RNG into the NG utility pipeline or use CNG will be made in the future as more discussions with the stakeholders are conducted.

INTRODUCTION The digester gas that is produced at Metro Vancouver's existing Lulu Island Wastewater Treatment Plant (LIWWTP) mesophilic digesters and digested sludge storage tank (DSST) is collected and burned in the plant's boilers to provide process and building heat. Surplus digester gas flows to the waste gas burners and is flared. Metro Vancouver desired to upgrade the surplus digester gas produced from the digesters and deliver pipeline quality biomethane (renewable natural gas, RNG) to the natural gas utility instead of flaring. The LIWWTP is a secondary wastewater treatment plant in Richmond, BC with effluent discharge to the main arm of the Fraser River. The plant was originally commissioned in 1973 and serves a population of approximately 200,000 people in the Richmond area. The liquid stream process includes coarse screening, primary treatment (pre-aeration grit removal and sedimentation), and secondary treatment (trickling filters, solids contact tanks and secondary clarifiers). The solids stream process includes gravity thickening for primary sludge, dissolved air flotation thickening for secondary sludge, anaerobic digestion, and digested sludge dewatering using centrifuges. Metro Vancouver engaged AECOM Canada Ltd. to provide design and construction engineering services at the LIWWTP to upgrade the surplus digester gas produced from the digesters to pipeline quality biomethane gas and deliver to the natural gas utility. The Sludge Gas Treatment (SGT) system is sized to upgrade surplus digester gas, which is defined as the portion of total digester gas not used by boilers for plant process and building heating needs, for a range covering the present surplus digester gas flow through to the design year of 2035. By upgrading the surplus digester gas, wasting events (flaring) will be minimized and greenhouse gas (GHG) emissions from the LIWWTP will be reduced. Construction of the LIWWTP SGT system was completed in September 2021 and it is currently in operation. DISCUSSION The focus of this discussion is on the challenges faced during the design and construction of the SGT system, including technology selection, fluctuating surplus digester gas flow, process design and control considerations, and lessons learned from project construction and operation. Technology Selection In order to permit the injection of digester gas that is produced at LIWWTP into the natural gas grid, it must be cleaned and upgraded to pipeline quality biomethane. Purification of digester gas involves removal of particulates, water, carbon dioxide, contaminants such as hydrogen sulphide and other trace contaminants. One of the main considerations for the evaluation of the available digester gas upgrading technologies was whether the manufacturer had proven installations with equipment manufacturers' support in North America. After review and consultation with equipment manufacturers of digester gas cleanup technologies, four technologies were considered for detailed evaluation: -water scrubbing -membrane separation -pressure swing adsorption -amine scrubbing. Some of the factors considered in the evaluation of the four technologies included: -Ability to upgrade digester gas quality to be in compliance with the natural has utility Biomethane Acceptance Specifications -Capacity -Turndown and expandability -Capital cost and life cycle cost -Carbon dioxide (CO2) waste gas stream disposal -Operating and maintenance costs -Ease of operation and maintenance -Noise level -Greenhouse gas emissions generation. Ultimately, water scrubbing was selected as the preferred digester gas upgrading technology for this project. Digester Gas Production The LIWWTP SGT system is sized to operate effectively at the design flows expected over the next 10-15 years. The surplus digester gas projections were based on digester gas production data (surplus flow to the waste gas burners) provided in process control reports from 2002 to 2015. The process control reports reveal that there are frequent changes in flow rate from the existing gasholder to the waste gas burners. The monthly average daily flow rate of digester gas over a 2-year period is presented in Figure 1. The significant flow variations would be below the minimum turndown of the SGT system, which would interrupt operation and significantly reduce the production of treated digester gas. Several options to attenuate the fluctuations were considered including running the boilers at steady state, using the existing gasholder, providing a new gasholder, increasing the size of the SGT system, and adding a small new boiler. The preferred approach was determined to be adding a new membrane gasholder to attenuate the surplus gas flow and decouple the SGT system from the existing gas management system. The new gasholder, shown in Figure 2, also acts as a control device for determining the digester gas feed rate to the SGT system. Process Design & Control Considerations The existing gasholder, which is connected to the digester gas header, maintains the digester gas at a constant pressure; the gasholder has a weighted piston which rides up and down as digester gas accumulates or is released from the gasholder. Primary control of the gas management system at LIWWTP is based on the piston level in the existing gasholder. When the piston level exceeds a specific setpoint, level control valves modulate open to allow surplus digester gas to the new SGT gasholder or to the waste gas burners. To provide a more stable flow for the SGT system, a number of control methods and gasholder storage volumes were reviewed, including: -time averaged flow control -constant flow based on surplus digester gas average daily flow -constant flow, fill and draw operation, -PID control operation, and -flow to level ratio control. Flow to level ratio control was selected as it provides a reasonably stable flow to the SGT system with low flaring and the lowest required storage volume. LESSONS LEARNED The lessons learned from the design and construction of the LIWWTP SGT project are summarized below: Fluctuating gas production can be managed through storage -Pressure conditions of the gas supply need to be measured and documented in detail in the early stages -Finding a balance between footprint and piping/equipment layout requirements -Programming/integration with existing facilities needs careful consideration -Changing weather conditions require a review of heat tracing requirements for piping and tanks -Options to recycle off-spec purified gas can further reduce wasting CONCLUSIONS The LIWWTP SGT System upgrades surplus digester gas to pipeline-quality biomethane (RNG), significantly reducing digester gas wasting events. In 2022, on average, the LIWWTP has seen a 78% reduction in wasting events when compared with previous years with no SGT system in operation. During summer months, the wasting events were reduced by as much as 99%. The system has been consistently producing greater than 98% methane and is projected to generate 60,000 gigajoules of RNG for the natural gas utility, enough to supply 660 typical homes.

Introduction Residual solids from wastewater treatment often require further processing prior to end use, beneficially or otherwise. Historically called sewage sludge, the industry refers to these residuals as biosolids if the final product meets specific federal and state requirements (WEF 2021). Historical applications for these materials face mounting pressures from cost and decreasing site options (Collins, 2019; Slaughter, 2013; USEPA, 1994; EREF, 2021). Another pressure emerging in the industry are per- and polyfluoroalkyl substances (PFAS) (Boxall et al., 2012; Kinney et al., 2006; Navarro et al., 2018; Sepulvado et al., 2011; Walters et al., 2010; Winchell, Wells, et al., 2022). Incineration of sludge and biosolids is a widely applied and accepted technology for addressing this suite of challenges because it provides a high level of control for municipalities. However, obtaining and maintaining permits to construct and operate facilities comes at a significant cost and resource commitments in addition to relatively complex operation and maintenance requirements (WEF, 2009). These complications create an opportunity for alternative technologies to enter the industry. Pyrolysis and gasification systems offer incineration alternatives while achieving similar objectives for mass and handling cost reductions. This paper will provide the Water Environment Federation (WEF) audience with an objective comparison of incineration, pyrolysis, and gasification technologies. Basic principles, process outputs, permitting, and equipment capital costs will get covered. The information will largely reflect the recent publication by the authors in WEF's peer-reviewed Water Environment Research journal (Winchell, Ross, et al., 2022). Basic Principles The primary differentiator, outside of temperature and products, between pyrolysis, gasification, and incineration processes is the amount of oxygen introduced into the high-temperature reactor (Figure 1). Pyrolysis thermochemically converts organic feedstock to carbon-rich char and a hydrocarbon-rich off-gas in the absence of oxygen. Gasification processes further refine the char and off-gas from a pyrolysis step using a gasifying medium (such as air, oxygen, or steam). In the presence of adequate oxygen, the primary constituents of sludge and biosolids carbon, hydrogen, oxygen, nitrogen, and sulfur are combusted to thermodynamically stable end products, such is the goal of incineration. The general arrangement of the process train for pyrolysis, gasification, and incineration is similar. Figure 2 depicts the sub-processes for thermally treating sludge or biosolids and indicates the processing train is categorically similar among the three technologies, with a few exceptions. The common input to all three technologies is dewatered sludge or biosolids. Typical outputs include gas-phase emissions from the stack and solid residuals (i.e., char or ash). Table 1 summarizes the fundamental differences among these three processes. Process Outputs Regardless of the thermal technology or site-specific considerations, each process results in solid and gas-phase emissions. The solid ash or char is collected from the thermal reactor or air pollution control equipment, while gas-phase emissions are ultimately emitted to the atmosphere through the process stack. During pyrolysis and gasification, off-gas production increases as temperatures increase, while char yields decrease due to the loss of volatile components (Chen et al., 2014; Yuan et al., 2015). Nearly all carbon is combusted, and volatile components are lost during incineration, resulting in ash comprised of inorganic minerals dominated by silicon, aluminum, iron, and phosphorus oxides along with alkaline earth minerals (Li et al., 2018; Tempest, 2013). Summaries of the ash and char characteristics and air emissions, including examples of allowed levels from operating facilities, from Winchell, Ross, et al (2022) will be presented. Permitting Permitting a gasification or pyrolysis facility differs significantly from an incinerator. The Clean Water Act and Clean Air Act have sections specific to 'incineration' of 'sewage sludge.' Further, both Acts include definitions specifying combustion of the sludge or biosolids as a critical characteristic of incineration, 40 C.F.R. § 60 (USEPA, 2011). However, there are no specific references to pyrolysis, gasification, or associated thermal oxidizers, and permitting requirements are subject to a case-by-case determination (Hambrick, 2021). To date, pyrolysis and gasification facilities have avoided the 'incineration' designation (Aries Clean Technologies, 2021; USEPA, 2013, 2016) and the associated regulatory requirements. Pyrolysis and gasification systems still must undergo an air permitting process similar to that required for an incinerator as outlined in WEF (2009). In general, the current regulatory framework provides pyrolysis and gasification systems a distinct advantage over sewage sludge incinerators if they can continue avoiding the 'incineration' designation. Equipment Capital Costs Several high-temperature equipment suppliers provided planning level capital costs for a single train of equipment from the point of dewatered sludge or biosolids delivery to the stack, including a handling system for residual solids. Figure 3 displays the cost information in cost curve fashion. The pyrolysis and gasification technologies offer a cost-benefit at lower processing capacities but become comparable to incineration at the 110 dry tonnes/day capacity. Given the cost advantages of pyrolysis and gasification technologies in small to mid-size treatment facilities, this is likely where these technologies will enter the wastewater market. Conclusions Primary advantages of pyrolysis and gasification systems versus a contemporary incinerator identified include operating characteristics, equipment sizing, air emissions, emissions regulations, potential char applications, and equipment costs. These advantages need to be weighed against the added complexity of equipment required for these processes. These advantages and disadvantages will be discussed and detailed in the full paper. Altogether, pyrolysis and gasification show promise as alternatives to incineration for some facilities, particularly small to mid-sized facilities, and the current and contracted-to-build installations will, over time, provide valuable information on real-world operating and maintenance requirements.

Background Portland Water District (PWD) has four wastewater treatment facilities (WWTFs) with a capacity of more than 25 million gallons per day. Two of the four facilities - East End and Westbrook process most of the solids in the system and were the focus of PWD's comprehensive approach to assess the current solids system and develop a strategic plan that outlines the necessary upgrades, process modifications, and state-of-good-repair projects that PWD should undertake during the next 20-year planning period. PWD began contemplating this planning effort not only due to aging infrastructure, but rather due to increasing concern over lack of biosolids management options and rising public concern around per- and polyfluoroalkyl substances (PFAS) in biosolids. Throughout New England, decreased biosolids management capacity has been a rising concern. Much of the region relies upon landfills and regional incinerators, but beneficial use (land application) has served as a reliable, sustainable option for a number of utilities. In Maine, land application had been an accepted practice, with good market understanding of the benefits of biosolids, including biosolids based compost and thermally dried products. In 2019, however, PFAS contamination was discovered at a Maine dairy farm that had historically land applied both biosolids and short paper fibers. This led the Maine Department of Environmental Protection (DEP) to promulgate soil screening standards for two PFAS - perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS). These screening standards were used to limit biosolids land application rates based on the concentrations of these two compounds, and the understanding that PWD might be able to land apply in the future served as an initial assumption of the study. Shortly after study initiation, the Maine legislature passed LD 1911, which prohibits the land application or sale of biosolids and biosolids-derived products in the state of Maine. While options were already limited before this new law, the only option for biosolids management in Maine is now landfill disposal. The passage of LD 1911 thus focused the biosolids master plan on technologies that significantly reduce volume and/or employ thermal destruction. Methodology The goal of this project is to create a 20-year system-wide implementable plan, including near- and long-term improvements that improve the reliability of PWD's solids handling assets while meeting the project goals of mitigating emerging contaminants risks, enhancing reliability and regulatory resiliency, and increasing the public's confidence in PWD's environmental stewardship. PWD worked with its consultant to create a master plan that has both near- and long-term improvements to improve the reliability of PWD's solids handling. Alternatives were evaluated based on regulatory, financial, social, and environmental goals and objectives. An overview of the master planning process is shown in Figure 1. Custom solids and energy models were created to reflect the operation of East End and Westbrook, which were used to determine alternatives for solids handling. The consultant team also provided PWD with estimated operational and capital costs, solids production, and energy requirements based on actual PWD unit costs. Throughout this process, the PWD and consultant team developed and evaluated seven alternatives at six workshops. The outcome of these workshops was a roadmap with several triggers rather than a final solution due to the uncertainty and expected changes in Maine's regulatory framework. Alternatives were evaluated using a mass and energy balance model that supported evaluation of both technical and operational performance. When combined with the capital investment required for each alternative, the model produces a net present cost (NPC) lifecycle cost of each alternative that, when compared to the baseline process condition, determines its financial viability. For this study, it was assumed that the planning horizon for the project would be 20 years. The alternatives evaluated are: -Alternative 0: Status quo. No operational or capital improvements. -Alternative 1: Modified baseline. Baseline operation with new dewatering and sludge storage. This alternative considers the possibility of sending dewatered solids to a merchant facility or to a landfill. -Alternative 2: Thin film Dryer. Westbrook dewatered solids hauled to East End, and the combined solids are dried in a thin film dryer and then disposed of at a landfill. -Alternative 3: PS AD + thermal dryer. Westbrook dewatered solids hauled to East End. East End primary sludge (PS) only mesophilic anaerobic digestion (AD) with thermal drying of all East End and Westbrook sludge. Landfill disposal with possible beneficial end use options in the future. -Alternative 4: Regional Pyrolysis. Westbrook and East End dewatered solids hauled to a PWD-owned regional pyrolysis facility, with either biodrying or thermal drying. Biochar is beneficially used. -Alternative 5: Regional Solar Drying. Westbrook and East End dewatered solids hauled to a PWD-owned regional solar drying facility. Landfill disposal with possible beneficial end use options in the future. Table 1 presents the results of the NPC analysis for these alternatives at a range of solids management costs, which are the largest contributors to the annual solids handling and processing costs. Note: Pyrolysis alternatives do not increase with rising tip fees, as it was assumed PWD had an agreement with the vendor to take the biochar at no cost. Sludge pyrolysis has not been demonstrated at PWD's size, so PWD decided the uncertainty with this technology was too significant at this high capital cost; therefore, PWD decided to continue to monitor the technology before making a final decision. The remaining alternatives were then evaluated based on non-cost factors including de-risking PWD on end use, sustainability, cost predictability, and improved reliability. Table 2 shows a summary of the goal factors for each of the alternatives. The modified baseline, which centers around improved dewatering, was found to be advantageous under current tip fees, and helps de-risk PWD as tip fee volatility increases. This was considered a 'no regrets' project as it both replaces aging infrastructure, and saves PWD money over the long term. With respect to the other alternatives, external factors, particularly the manner in which Maine DEP does or does not permit certain technologies, will affect which alternative should be implemented. As a result, a roadmap was made with key regulatory, market, and other implementation triggers to help guide PWD's actions in the next five years. The roadmap is presented as Figure 2, with the 'no regrets' project serving as the starting point (e.g. will be implemented). Key triggers will cause PWD to go on a certain path of the map, while additional triggers will further refine the likely or viable options. The final two branches (red and orange) of the roadmap are highly unlikely but could still be an outcome. The three key triggers are tip fees continue to rise, landfills reject biosolids, and tip fees stabilize or drop. This adaptable model allows PWD to make immediate improvements that will result in cost savings (dewatering upgrades and thickened sludge storage), while allowing for planning in the face of continuing regulatory flux. It is anticipated that over the next few years, Maine's regulatory approach will stabilize, clarifying the appropriate path forward. Conclusions While state and federal biosolids regulations are still uncertain, PWD can take the following actions recommended by the master plan: -Engage with regional partners now. Should support exist (both from Maine DEP and peer utilities) for regionalization, PWD and its potential partners would have time to determine challenging aspects of partnership such as governance. -Continue to engage with service providers as they explore merchant regional solutions. The master plan established a range of tip fees at which it could be advantageous for PWD to secure long-term management capacity. -Conduct a preliminary design project for the no-regrets projects at East End and Westbrook. This project would provide PWD with a basis of design report (BODR) in which dewatering technology and location would be selected as well as selection of size and location for sludge storage tanks at East End. The BODR would also include evaluation of conveyance of cake, automation of the screw press, and polymer changes at Westbrook. -Continue to engage Maine DEP on technology updates and data updates on PFAS mitigation. -Explore funding mechanisms and continue discussions with vendors on viable solutions. -Visit dryer and other vendor installations.

Introduction In order to better understand the fate and transport of PFAS compounds in wastewater sludge undergoing thermal combustion, a bench-scale system, that mimics a full-scale biosolids incineration, was constructed. Two batch studies were conducted with the system in 2020 and 2021 to investigate: 1) the decomposition and removal efficiency (DRE) of the PFAS in biosolids; 2) the residual PFAS concentrations in the ash, 3) the PFAS concentrations in the flue gas, and 4) the effect of operating parameters on the performance. The operating parameters evaluated were combustion temperature and gas residence time. Methods The two studies are identified as the 2020 and 2021 studies in this abstract. The feed sludge samples used for the two studies were obtained from two municipal wastewater treatment plants. While the same schematic of the bench scale testing system (e.g., a silica quartz tube) was used for the two studies, the sizes of the tubes were different. For example, the length and outside diameter (OD) were 54.0 inches and 2.0 inches for the 2020 study. In order to increase the gas residence time (GRT), the 2021 study used a larger tube with a length of 78.0 inches and an OD of 4.0 inches. As shown in Figure 1, the sludge sample was fed into the reactor tube by a sample boat. The average sludge sample residence time (SRT) in the reactor tube was approximately 5 min for both studies. The reactor tube consisted of three zones. The temperatures over Zone 2 (effective length) of the reactor tube were set 1,150 °C (+1 °C, -51 °C) for the 2020 study and 1,150 °C (+21 °C, -58 °C) for the 2021 study. Air was injected into the reactor tube from the feed end at a constant rate to achieve a pre-set GRT. The GRT was defined based on the volume over the effective length and the actual airflow at 1,150oC. The combustion flue gas was collected by the impingers on the exhaust end of the reactor tube. The impinger setup consisted of four impingers in series. Each 2-L impinger was filled with DI water at a volume of 1.5 L. The above operating conditions are summarized in Table 1. The 2020 study consisted of three triplet tests. Each triplet test generated one impinger sample. The residual ash from the triplet tests was combined to have one ash sample because the amount of ash generated from one triplet test was not enough for performing lab analysis. The 2021 study also consisted of three triplet tests. Due to the large amount of samples used, each triplet from the 2021 study generated one impinger sample and one ash sample. All samples were analyzed for PFAS by Eurofins/TestAmerica with 12-targeted analytes for the 2020 study and 36-targeted analytes for the 2021 study. Fluoride was analyzed for all the impinger samples by the same laboratory for PFAS. Test Results For conciseness, only the major PFAS compounds such as PFOA, PFOS and Total PFAS are presented in Table 2. As shown, total PFAS concentration in the raw sludge was 118 ng/g and 59 ng/g for the 2020 and 2021 studies, respectively. Due to the low total PFAS concentrations, the raw samples were spiked with PFOA, PFHxS, PFHps and PFOS to a total PPFAS level at 31,292 ng/g and 5,893,800 ng/g for the 2020 and 2021 studies, respectively. The purpose of the spiking was to study the PFAS decomposition capability by the combustion process. As shown in Table 2, the spiking level for the 2021 study was 188 times higher than that of the 2020 study. The PFAS level in the ash sample from the 2020 study was much lower than that of the 2021 study (0.32 ng/g versus 11.0 ng/g). This may be due to the large difference in the feed PFAS spiking. The total PFAS level in the ash sample from the 2021 study was 26.1 ng/g at maximum (i.e., 26.1 µg/kg) and 11.0 ng/g on average under the total spiked PFAS concentration of about 5,900,000 ng/g. These residual PFAS results indicate that the ash after the thermal combustion process can meet the PFOS permit level (50 µg/kg) for land application imposed by the State of Michigan. PFAS Decomposition Efficiency - As shown in the schematic (Figure 1), the impinger sampling system was designed to catch the PFAS in the flue gas from the reactor tube, which represents the flue gas coming directly out of the furnace but before the air pollution control (APC) equipment for full scale incineration projects. As mentioned in the experimental setup section, the impinger samples were analyzed for fluoride. The fluorine balance was conducted based on the measured PFAS level in the spiked sludge samples and the measured fluoride concentration in the impinger samples. A fluorine balance ranging from 78% to 88% was achieved in the combustion tests. The fluorine balance above 80% indicates a reasonably good mass balance on the combustion system, thus using total PFAS balance around the combustion reactor to calculate the decomposition efficiency is valid. The mass balance results and the decomposition efficiencies from the two studies are presented in Table 3. As shown, the PFAS mass in the feed was about 3,000 times more in the 2021 study than the 2020 study due to that the higher spiking concentration and larger sample mass were used for the 2021 study. However, the total recovered PFAS mass based on the impinger and ash samples were not significantly different between the two studies. The average total PFAS recovery by the impinger and the ash samples is 207.9 ng and 243.8 ng for the 2020 and 2021 studies, respectively. Therefore, the PFAS mass destroyed in the 2021 study was about 3,000 times that of the 2020 study, which was reflected by the PFAS decomposition efficiency. As shown, the PFAS decomposition efficiency based on total PFAS (sum of the 36 analysts) was at a level of 99.9999% (6 logs) for the 2021 study and 99.67% (close to 3 logs) for the 2020 study, on average. The major difference in operating conditions between the two studies was the gas residence times - 2 seconds for the 2020 study and 4 seconds for the 2021 study. The two tests were run at the same combustion temperature of 1,150oC. Therefore, it was believed that doubling the gas residence time from 2 s to 4 s improved the PFAS decomposition efficiency. Estimated PFAS Level in Flue Gas - The PFOA, PFOS, and 6:2 FTS levels in the flue gas were estimated based on their mass caught by the impinger divided by the total air volume (in m3 at STP) supplied during each triplet batch. The estimates represent the flue gas PFAS levels at the point before the air pollution control (APC) equipment for full-scale systems. The estimated flue gas PFOA, PFOS, and 6:2 FTS concentrations are summarized in Table 4. Statistical analysis indicates that even though the variability of concentrations within each triplet batch is large, the average concentrations of PFOA and PFOS in the flue gas obtained from each study are significantly different. The average flue gas PFOA and PFOS levels for the 2020 study were about 132.3 ng/m3 and 152.7 ng/m3, respectively. However, the average levels of PFOA and PFOS for the 2021 study were about 60.8 ng/m3 and 59.4 ng/m3, respectively, which are below the permit levels of 70 ng/m3 imposed by the State of Michigan for the air emission. It must be noted that the PFOA and PFOS levels in the flue gas estimated by the two studies represent the concentration before the APC equipment. The results from the 2021 study suggest that the air combustion operated at 1150oC and 4 seconds GRT can meet the emission requirements. Conclusions This bench scale study demonstrates that thermal combustion can be effectively and efficiently utilized to achieve near complete PFAS decomposition in the biosolids. The ash residuals generated from the two studies conducted at a combustion temperature of 1150oC and GRT of 2 and 4 seconds meet the PFAS requirements for biosolids land application. The estimated PFAS level in the flue gas indicates the potential of the combustion technology to meet the air emission requirements at 70 ng/m3 for PFOA and PFOS imposed by the State of Michigan. The gas residence time of 4 seconds at a combustion temperature of 1150oC improved the total PFAS decomposition and lowered the air emission for PFOA and PFOS, compared to the 2 seconds GRT.

Introduction: Anaerobic digestion is a proven technology to stabilize solids from water resource recovery facilities (WRRFs) and produce biogas. Enhancing anaerobic digestion would increase the volatile solids reduction (VSR), biogas production, and reduce the residual biosolids. The objective of this research was to explore how much the VSR could be increased in digestion with the addition of new technology: Microbial Hydrolysis Process (MHP). Typically, a well-performing anaerobic digester can achieve 55 percent VSR when fed a combination of primary and secondary sludge from a WRRF. High-performing digestion systems can achieve 60 percent VSR or higher, but none (until now) have achieved over 70 percent VSR. Jacobs with professors at Brigham Young University (Hansen, Jaron C., et al., Biofuel Research Journal Vol. 8 Issue 3 2021), developed the Microbial Hydrolysis Process using Caldicellulosiruptor bescii (C. bescii), a hyper-thermophilic bacterium that enhances the performance of any anaerobic digestion process. The MHP digestion process flow diagram is shown in Figure 1. The C. bescii bacterium and associated enzymes hydrolyze cellulose and other recalcitrant volatile solids that are otherwise resistant to digestion into volatile acids. These hydrolyzed volatile solids are fed to an anaerobic digester where methanogens convert them into biogas. One configuration of MHP feeds digestate from an anaerobic digester to a hydrolysis tank populated with C. bescii for a hydraulic retention time of at least 2 days at 75 degrees C. The hydrolyzed digestate is then returned to the digester to complete the digestion process by converting volatile acids into methane and carbon dioxide. MHP is compatible with any anaerobic digestion process including mesophilic anaerobic digestion (MAD), thermophilic anaerobic digestion (TAD), and thermal hydrolysis process (THP). The increase in VSR results in corresponding increases in biogas production and reductions in residual biosolids. The value of the additional biogas and cost savings of producing less biosolids reduce the operating costs of a WRRF. Methodology: The performance of anaerobic digestion with MHP was tested at lab-scale and pilot-scale systems on solids from three different WRRFs: City of Gresham Wastewater Treatment Plant in Gresham, OR with MAD and fats, oils, and grease (FOG) addition; Encina Water Pollution Control Facility (WPCF) in Carlsbad, CA with MAD; and Oakland County's Clinton River WRRF in Pontiac, MI with THP and MAD. The lab-scale system consisted of a test and control system: each with a 10 Liter (L) digester and a 5L hydrolysis tank. Figure 2 is a picture of the MHP digestion lab-scale system and Figure 3 is a process flow diagram of the system. The pilot-scale system consisted of a test system with a 1,200L digester and a 500L hydrolysis tank and a control system with a 1,200L digester. Figure 4 is a picture of the pilot-scale MHP digestion system and Figure 5 is a process flow diagram of the system. All tanks were mixed, heated, and automatically fed from digester feed tanks. The test and control systems were operated to simulate the full-scale digester operation for feed, retention time, and transfer rate between the digester and hydrolysis tank. Characteristics of the feed and contents of the digesters and hydrolysis tanks were measured using standard methods. The stability of the digestion process was monitored measuring Volatile Fatty Acids, Alkalinity, and Ammonia. The VSR of the digesters was the key indicator of performance and was determined from the TS and VS fed to the digesters compared to the TS and VS withdrawn from the digesters. Lab-scale tests for Gresham and Encina were conducted in the Gresham lab. Pilot-scale tests for Oakland County were conducted in the Clinton River WRRF lab. Labs at each WRRF were used to measure the characteristics of the feed and performance of the full-scale digesters. Findings: The digestion performance of the three WRRFs are indicated by the VSR. Results from lab-scale, and pilot-scale digestion systems have demonstrated significant increases in VSR compared to already high-performing digestion systems (e.g., THP and MAD). VSRs were observed to increase from 60 percent without MHP to greater than 75 percent with the addition of MHP. Figures 6-8 show the VSR results of the test and control systems compare to the full-scale systems. In all cases the MHP increased the VSR from current operation of 58-60 percent to over 75 percent VSR. Results were used to calibrate a process model (Sumo) to predict digestion performance for full scale facilities with different feed characteristics. Based on the results, conceptual designs were prepared for implementation at three WRRFs with three different technologies: MAD, TAD, and THP and MAD. The details of these designs are being reviewed by each utility and can be presented in the full paper. Significance: The significance of the research and development of MHP is the discovery of a new technology that enhances the performance of anaerobic digestion to the highest level achievable to date. Anaerobic digestion performance increased with the addition of MHP in tests on three different WRRFs. MHP increased the VSR from 60 percent to over 75 percent. The increase in VSR corresponded to a 25% increase in biogas production and a 25% decrease in biosolids production.

Abstract: Introduction: The San José-Santa Clara Regional Wastewater Facility (RWF) provides secondary and advanced tertiary wastewater treatment for the cities of San José and Santa Clara, California and multiple tributaries. The RWF is co-owned by the cities of San Jose and Santa Clara, and is operated by the City of San Jose (City). The RWF has a rated capacity of 167 million gallons per day (MGD) and processes wastewater solids using anaerobic digestion. The RWF has used cogeneration engines for over 30 years to provide heat and power for the facility. However, the existing cogeneration system reached the end of its useful life. The City decided to replace the existing cogeneration engines with an updated system to continue providing the RWF's heat and power demands as part of its commitment to sustainability. The San Jose Cogeneration Facility Project was designed and constructed through a progressive design-build process. The design was centered around four 3.5 MW internal-combustion, engine-driven generator units. The Cogeneration Facility is shown in Figure 1 and the engine room in Figure 2. Table 1 is a project fact sheet with key specifications. The 14 MW system has the capacity to meet the projected RWF electrical demand of 13 MW in 2040. Space for a fifth 3.5 MW unit is provided to have a firm capacity of 14 MW in the future with one unit out of service. Experience throughout the planning, design, construction, and commissioning of the project is shared. Insights discussed: -Early selection and procurement of cogeneration units -Integration of cogeneration with standby power systems -Biogas treatment and management -Fuel blending of biogas with natural gas (and provisions for future landfill gas) -Emission requirements met with post-combustion treatment -Heat recovery and management -Business-case decision making throughout the project -Startup considerations Discussion: The project included early selection of the cogeneration and gas treatment systems in the initial design stage. By selecting the equipment early in the design, subsequent design stages were tailored to known specifications. The cogeneration units were selected through an evaluated bid process that quantified the value of electrical efficiency, fuel blending capability, gas compression requirements, cost of parts, and maintenance requirements (triple bottom line analysis). The cogeneration facility is integrated with two separate utility power feeds and standby generators. This integrated power system provides a reliable power supply for the RWF. Protective relays were included to meet the electric utility interconnection agreement and allow for excess power to be supplied to the utility grid if necessary. The design provides for supplemental natural gas to be replaced with landfill gas in the future. Because of the significant amount of natural gas required (as much as 50 percent of the fuel energy content), prior to landfill gas availability, to meet the plant power demand, these cogeneration units need to meet the stringent Bay Area Air Quality Management District (BAAQMD) emission requirements of a natural gas fueled cogeneration system. Digester gas treatment protects both the engines and the engine exhaust gas treatment equipment. The biogas treatment system is shown in Figure 3. Biogas treatment includes hydrogen sulfide removal (initially iron sponge, now a proprietary media), moisture reduction, siloxane removal via activated carbon, and particulate removal. In this case, gas treatment followed gas compression and moisture removal. Consequently, the gas treatment occurs at a relatively high pressure of 50 psig. Provisions for the incorporation of future landfill gas were also included in the piping design. Each engine is equipped with a dedicated gas blending system to allow operation using any blend of biogas and natural gas. The gas blending system responds to changes in digester gas production (via gas holder level) to achieve a power output setpoint without requiring a system shutdown, though the peak power output of a cogeneration unit reduces as the natural gas quantity increases. Exhaust gas treatment was provided to meet BAAQMD emission limits. Exhaust gas treatment consisted of selective catalytic reduction (SCR) for nitrogen oxide (NOx) reduction and an oxidative catalysis for carbon monoxide (CO) and volatile organic carbon (VOC) reduction. The most difficult contaminant to treat was NOx. The BAAQMD requirements limited the facility to 0.124 g/bhp-hr, compared to federal requirements of 1.0 and 2.0 g/bhp-hr for natural gas and biogas fueled engines respectively. Heat generated by the cogeneration units is recovered from the engine and exhaust gas to provide process heating demands as well as selected building heating. New dual-fuel auxiliary boilers provide supplemental and backup heating for the RWF. Rejection of low temperature heat that can't be beneficially used is provided by cooling towers. The anaerobic digestion system at the RWF is being converted from mesophilic anaerobic digestion to a temperature-phased anaerobic digestion (TPAD) system. The heat supply system was designed to accommodate the higher temperatures and heat requirements for the TPAD system. The heat recovery and hydronic heat supply system was coordinated with the TPAD project team to meet the heating demands both in terms of temperature and amount of heat while maximizing heat recovery from the engines. Using the progressive design-build delivery method enabled collaboration between the Owner and the Design-Builder, particularly during the early design stages. Approximately halfway through preliminary design, it became clear that the project required value engineering to reduce costs within the City's budget. Approximately 20 percent of the project cost was reduced through a value engineering effort with the City and the Design-Builder. Business case evaluations were conducted throughout the project for decision-making based on meeting multiple objectives of economic, environmental, social, and operational categories. Life cycle cost to benefit ratios were compared for different options to guide selecting the best option. There were several startup procedures that could be followed on other projects. The biogas treatment system was tested and commissioned using the boilers prior to sending treated gas to the engines. The engines were started on natural gas first to test ancillaries prior to running on biogas. Lessons Learned: -Early selection of cogeneration units and gas treatment system enables an efficient design process -Integrating the utility power feeds with the cogeneration units and standby generators results in a reliable plant power supply -Additional exhaust gas treatment (such as oxidation catalysts and selective catalytic reduction) can be used with comprehensive biogas treatment to meet strict air quality management districts. -A fuel blending system for biogas and natural gas, provides operating flexibility -Heat recovery from the engines can be designed to be compatible with a higher temperature thermophilic digestion process. -Costs can be controlled during design with a progressive design build procurement and value engineering.

Introduction and Objectives Our scientific understanding of per- and poly-fluoroalkyl substances (PFAS) in our environment has evolved rapidly in the last several years and PFAS have increasingly gained attention from the public, scientific, and regulatory sectors due to their carcinogenic and reproductive and endocrine disruptive nature. Previous research has illustrated that water resources recovery facilities (WRRF) are notable PFAS emission routes to the environment, both liquid and solid discharge routes. Despite industrial phasing-out of some PFAS and increasing source management of industrial discharges, PFAS are expected to be present in wastewater solids for the foreseeable future. According to Northeast Biosolid and Residual Association (NEBRA), more than seven million dry tons of wastewater solids were produced at WRRFs in 2004 and solids management practices have resulted in the release of approximately 3000 kg PFAS per year to agricultural lands and landfills (Venkatesan and Halden, 2013). Much work has been done to develop and demonstrate wastewater treatment technologies to destroy PFAS compounds (mineralize to non-fluorinated end-products) in wastewater solids, but few studies have documented the practical application of PFAS destruction technologies for wastewater solids or estimated the cost of implementing those technologies. Our team conducted an evaluation for the Minnesota Pollution Control Agency (MPCA) to document the technology options that could be implemented today to remove and destroy PFAS within municipal wastewater effluent, compost contact water, landfill leachate, and municipal wastewater solids. The objectives of this project were to: -establish a framework for determining which technologies meet the definition of commercially available and effective for PFAS destruction -conceptualize upgrades to destroy PFAS at existing WRRFs -estimate the cost of completing these upgrades for a range of WRRF capacities. Systems were conceptualized for facilities ranging from 0.1-10 MGD. For capacity greater than 10 MGD, a regionalized option was considered. This paper will highlight the findings from wastewater solids portion of the study. This information will be valuable for utilities looking to implement PFAS destruction technologies as regulations around PFAS evolve rapidly. Target PFAS Initial work for the study involved selecting a set of PFAS to represent the range of PFAS known or predicted to be in wastewater solids. Selected PFAS are well-described in PFAS treatment literature, frequently detected in wastewater solids, and diverse in chain length and functional groups. Table 1 lists the selected compounds, assumed typical and high concentrations in wastewater biosolids, and associated target post-treatment. The selected PFAS are generally long-chain perfluoroalkyl acids (PFAAs) or are precursors to PFAA formation, which research has shown to partition into solids. Representative concentrations of PFAS were selected from available literature. Technology Screening PFAS destruction technologies were screened for their ability to consistently remove at least one identified PFAS to below the currently accepted laboratory detection limit, as outlined in Table 1. Technologies were further screened by their readiness for full-scale implementation. Wastewater solids PFAS destruction technologies passing the screening included pyrolysis with thermal oxidation of the process gas, gasification with thermal oxidation, and supercritical water oxidation (SCWO). Pyrolysis and gasification systems were considered to use similar enough equipment to be evaluated as a single alternative for conceptual design. Pyrolysis/gasification systems included a thermal dryer as part of the equipment assembly since both technologies require high solids content. Conceptual Design and Cost Estimating A conceptual design was created for both short-listed PFAS destruction alternatives and for solids production rates of 1, 5, and 10 dry tons per day at a given WRRF, corresponding roughly with the plant influent flow rates used for the liquids portion of the study. The feed solids to the pyrolysis/gasification process were assumed to be dewatered to 25 percent total solids. For SCWO, the feed solids were assumed to be screened and dewatered to 15 percent total solids. Construction cost estimates (AACE Class 5) were prepared from recent project estimates and input from vendors. The construction costs were plotted against the system feed rate to create cost curves for each alternative. One example of a cost curve for pyrolysis/gasification is provided as Figure 1. The construction cost curves for pyrolysis/gasification and SCWO, and parameters used to develop each, will be included in the paper. Additionally, a conceptual design for a regional pyrolysis/gasification facility for wastewater solids was developed to represent another approach for utilities. Our findings showed that due to high costs associated with PFAS treatment, regional approach might become viable for smaller facilities (facilities less than 10 MGD). A regional facility would receive dewatered solids from two or more individual WRRFs within a reasonable hauling distance. Fifty dry tons per day was assigned as a representative capacity for a regional PFAS destruction facility. Operation and maintenance costs estimated for recent pyrolysis/gasification projects were assembled to select representative 2022 O&M costs for a 50 dry ton per day facility. A 20-year lifecycle cost analysis was prepared and tested for sensitivity to variations of the tipping fees and interest rates. This paper will include the results and conclusions from the lifecycle cost analysis of the regional facility concept. Conclusion This study documents the cost of implementing currently available technologies to destroy PFAS in wastewater solids. For pyrolysis/gasification, the O&M costs per dry ton trended lower as the system capacity increased, indicating that smaller utilities could reduce costs if they formed a partnership and developed a regional PFAS destruction facility. Demonstration testing of SCWO systems is expected to provide evidence to clarify if similar results can be expected for SCWO systems.

The Washington Suburban Sanitary Commission's (WSSC) Bioenergy Program is developing a $271 million regionalized solids handling facility at the Piscataway Wastewater Treatment Plant (WWTP) in Accokeek, Maryland. WSSC is a water and wastewater utility that serves approximately 1.8 million residents of Prince George's County and Montgomery County, Maryland. The facility will receive biosolids from multiple WSSC facilities in order to consolidate treatment and produce Class-A biosolids using the thermal hydrolysis process (THP) and new anaerobic digesters. The project is being implemented through a progressive design-build delivery that is in construction, with startup expected in mid-2023. The program includes the production of renewable natural gas (RNG) from biogas and injection of RNG to the Washington Gas Light (WGL) pipeline system. WSSC's approach to its RNG program is self-implemented. By comparison, other utilities have pursued RNG programs with varying levels of public-private partnership (P3) for some combination of ownership/operation of RNG production facilities, contracting with end user(s) for the use of RNG in vehicle fleets, sales of the environmental attributes for RNG use in vehicles, and/or ongoing verification and management for the program. A guiding principle behind WSSC's approach is to accept risks associated with RNG sales and renewable identification number (RIN) markets, recognizing that the benefits from managing its program can be greater by allowing risk rather than seeking pricing certainty for RNG production and renewable credits. Components of WSSC's approach include the following: RNG production. A water wash scrubbing system is being installed for conversion of biogas to RNG. WSSC staff will operate and maintain the gas treatment system at the Piscataway WWTP. WSSC could elect to pursue contract maintenance of the gas treatment equipment based on its experience following startup of the facilities. Daily RNG enrollment to the WGL pipeline based on production will be by WSSC. The anticipated RNG production is 3.4 million therms over the first four years of production. Energy utility. Where WGL is the natural gas (NG) infrastructure utility for the Piscataway WWTP, in Maryland's deregulated NG framework, an energy utility sources and supplies NG to end users. WSSC has registered as an energy utility for the Maryland market and will use this approach to deliver RNG to an in-state end user. In addition, WSSC will source NG for use at its facilities, including a 4.5 megawatt cogeneration system at the Piscataway WWTP which is part of the Bioenergy Program to provide power, steam for THP, and other process heat. An alternate approach would be to utilize an existing energy utility as an intermediary for the transfer of produced RNG and purchase of pipeline NG. However, this approach would involve the sale of the RNG fuel value to that utility and likely some portion of the environmental attributes. If WSSC sold its gas to an out-of-state end user, the step of becoming an energy utility likely could be bypassed, but an intermediary might be required to use WSSC as the RNG source and to source additional NG supply for the end user. RNG sales. To generate RINs from RNG, the fuel must be utilized in vehicles. From early in the development of the Bioenergy Program, WSSC identified the local transit agency in Montgomery County, Maryland, the utility's service area, as an end user for RNG. WSSC plans to become the sole provider of NG to the County, sourcing pipeline NG to supplement its RNG production to meet the transit fleet's fuel needs, as well as NG use at other county facilities. For the RNG, the environmental attributes will remain with WSSC. Montgomery County may pursue electrification of its transit fleet over the longer term. In this event, WSSC can seek another end user for RNG or consider the development of RNG-fueled power production for the transit fleet and the production of eRINs for electric vehicle charging. Program verification. Key parts of establishing a RNG program are the initial producer registration with USEPA, third party engineering review, and ongoing outside auditing for RIN verification. WSSC issued a request for proposals (RFP) for this work and ultimately contracted with Weaver LLC to perform these functions. The initial data collection regarding the facilities has occurred so that Weaver will be positioned to perform its engineering review and enroll the facilities with USEPA as they come online. RIN sales. WSSC has developed a sales solicitation for RINs from the program and will issue it for response in early 2023 in anticipation of starting production later in the year. Multiple entities are potential purchasers for RINs. Under the Renewable Fuel Standard (RFS), a group of obligated parties, typically fuel refiners, are required to use renewable fuels or purchase RINs as credit against their use. This generates the market for RINs. In addition to these companies, brokers also serve as intermediaries to bundle RIN credits for sale to the obligated parties. Ultimately, the solicitation is structured to select based on qualifications as well as the buyer providing the highest percentage of the Oil Price Information Service (OPIS) index price for D3 RINs (a cellulosic fuel category associated with RNG production from municipal wastewater) to WSSC as compensation for the credits. Ongoing program management. Because of its size, WSSC has a dedicated energy management team. This team has been instrumental in developing the self-implemented approach for the RNG program. In addition to its in-house staff, WSSC has used specialty consultants in addition to the program verification consultant for assistance in establishing itself as an energy utility. As the program moves from establishment to execution, WSSC will have the flexibility to maintain program functions in house or to bundle functions into outside contracts that it will manage going forward. The RNG portion of the Bioenergy Program is anticipated to generate a net revenue of approximately $9.6 million in the first four years of operation.

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.