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PROBLEM STATEMENT/PURPOSE: Prince William County Service Authority (PWCSA) owns and operates the H.L. Mooney Advanced Water Reclamation Facility (AWRF) in Northern VA. The AWRF is nestled in a residential community with parks and a walking path along the property line. The AWRF first implemented odor control in 2001, and subsequently upgraded the system in 2011 to provide odor control for preliminary treatment and solids thickening processes. To further reduce odors at the AWRF's property line and beyond, PWCSA is completing a design-build project that includes the assessment of odors at the AWRF through sampling and dispersion modeling, evaluation of odor control technologies, and the design and construction of the chosen system. The purpose of this abstract is to present the odor sampling, monitoring, and extensive dispersion modeling that led to the current design (2022) and future construction (2023) of a 95,000 CFM centralized odor control facility at the AWRF.

BACKGROUND:
The AWRF is located in Woodbridge, VA, approximately 30 miles outside Washington, DC and is in close proximity to several livable communities, nature parks, and walking paths. The AWRF is designed to treat 24 million gallons per day (mgd) average daily flow with current flows in the 14 to 16 mgd range. The AWRF has an existing packed tower chemical scrubber odor control system that treats odors from preaeration, screening, grit removal, and gravity thickening processes at the AWRF. Odorous air from solids dewatering and incineration are routed out of a high stack for improved dispersion. However, odor control improvements are needed to reduce odors within the AWRF site and reduce odor excursions into neighboring residential communities and walking paths outside the AWRF property line.

METHODOLOGY:
In the summer of 2021 odor sampling was conducted at various source locations throughout the AWRF to characterize the odors onsite coming from untreated sources and assess the treatment of the existing odor control facility. Odor sampling was completed during summer months to obtain samples under worst-case conditions (warm weather, higher anticipated odors). The sampled untreated process sources included the equalization basins, primary clarifiers, aeration basins, solids processing building odor exhaust (untreated odors routed to the high stack), and the incinerator exhaust stack. In addition to the untreated odor sources, sampling was also completed on the chemical scrubber inlet and outlet to assess the system performance. The odor sampling completed included: -US EPA Surface Emission Isolation Flux Chamber -Grab samples collected for olfactory odor analysis by ASTM E679 -Odor speciation using ASTM D194 -Reduced sulfur compounds using USEPA Method TO-15 (GC/FPD detector) -Field measurement of H2S using Acrulogs and Jerome 631X H2S meters -Ammonia, Amines, and Dissolved Sulfide with Colorimetric Detection Tubes -Temperature and pH Sampling data was evaluated and used to characterize the types and concentrations of odor species present at the AWRF, and to determine the odor emission rates from each odor source for use in the dispersion model.

RESULTS:
The results of the sampling showed the solids processing building exhaust to have the highest dilution to threshold (D/T) value, followed by turbulent zones of the primary clarifiers, anoxic stages of the aerobic basins, and quiescent zones of the primary clarifiers. The chemical scrubber exhaust results showed the system to be effectively reducing odors from the treated sources. The speciation sampling resulted in the detection of four odor compounds including hydrogen sulfide, methyl mercaptan, dimethyl sulfide, and dimethyl disulfide. Ammonia was also detected in samples from the solids processing building. D/T results were used to develop the odor emission rates (OERs) for each odor source. OERs were developed by translating sampled values into odor units per second (OU/sec) based on airflow and odor magnitude. The OERS were used as inputs for the baseline emissions model, also known as the AERMOD dispersion model. Meteorological data for the AERMOD dispersion model was sourced directly from the National Oceanic and Atmospheric Administration archives for representative observation sites. The most recent three years of available data (2018–2020) were used in this analysis and surface data was obtained from the Quantico Marine Corps Airfield, which is 8 miles south of the AWRF. The resultant impacts calculated by AERMOD are expressed in odor units per cubic meter of air (OU/m3) and can be compared directly to the sampled D/T values. Several scenarios of modeling were completed to evaluate existing conditions, identify the most impactful sources of odor dispersion, and assess potential treatment solution results for the sources. The baseline dispersion model, or existing conditions scenario, showed the predicted impacts from the sampled odor sources on site and their impact outside the AWRF fence line. Figure 1 provides the baseline scenario potential impacts. The worst-case D/T concentrations predicted to reach a given area are shown with the color/label. Based on the baseline scenario, the odor source impacts of the AWRF would be noticeable, and potentially a nuisance, for all areas above 7 D/T (shown in yellow in Figure 1). This includes the communities to the north and east of the AWRF, which have maximum odorous impacts of 7 to 10 D/T. The wide impact of the 3 D/T contour extends beyond the frame of this view, which suggests that the AWRF could potentially contribute to ambient odors greater than 1 mile from the fence line. Individual sources were modeled and showed the solids processing building exhaust and the aerobic basin anoxic zones to have the greatest D/T dispersion impact. Before additional treatment options were evaluated, an odor impact criterion, or D/T fence line goal, was developed with PWCSA during several workshops. Virginia odor criteria are plant-specific, and a survey of Virginia plants showed criteria generally range from 5 to 10 D/T with different averaging time requirements. It was determined that the impact goal should be one that minimizes the risk of negatively impacting neighbors but is balanced with controlling increased cost that will be incurred if goals are excessively tight. For PWCSA, the recommended goal of 100 percent compliance with 7 D/T (1-hour impact goal) at the fence line was used for the evaluation of the model. Once the odor impact criterion was determined, six (6) additional modeling scenarios were developed to evaluate the impacts from treating/reducing odors from the untreated sources. The scenarios were as follow: 1.Treatment of solids processing building exhaust (assumed 90% D/T reduction from solids processing) 2.Coverage and treatment of the primary clarifier odors (assumed 95% D/T reduction from solids processing) 3.Combination of 1 and 2 (treatment of solids processing and primary clarifier odors) 4.Combination of 2 and treating EQ basin odors (assumed 50% D/T reduction from EQ basins) 5.Combination of 2 and covering and treating odors from the aerobic basin anoxic zones (90% reduction of odors from anoxic zones) 6. All control alternatives combined The different modeled scenarios showed the greatest odor reduction results for control scenario 6 (all sources treated), followed by control scenario 3 (primary clarifiers and solids processing building treated). Although control scenario 6 reduced the 7 D/T line impact slightly more than control scenario 3, both scenario results show benefit and bring the 7 D/T line close to the fence line. The model predicted dispersion results from scenario 3 are shown in Figure 2. All six of the scenario results will be shown in the presentation.

DISCUSSION/CONCLUSIONS:
The sampling and modeling results were used to identify the primary clarifiers and solids processing building as additional sources for odor control treatment at the AWRF. Once the sources were determined, a capacity assessment was completed on the existing system which showed it did not have sufficient capacity to treat the additional sources. A complete treatment technology evaluation was completed for the AWRF based on the airflows, odor species present, and required treatment for dispersion. Ultimately, the team decided to move forward with a new centralized chemical scrubber facility re-using the existing vessels and a new vessel to meet the design capacity of 95,000 CFM. Chemical scrubbers were chosen based on the sampling results, odorous airflow capacity requirements, and site space constraints. The presentation will provide insight and potential project path solutions for other utilities looking to evaluate the odor impacts from their treatment facilities on neighboring communities, experiencing odor complaints, or wishing to evaluate dispersion modeling uses.

ABSTRACT A brewery wastewater treatment plant (WWTP) experienced high hydrogen sulfide (H2S) concentrations in and around the biosolids handling building which led to concerns around worker safety, overloading of the existing odor scrubber, and odor complaints from the surrounding neighborhoods. The Brewery WWTP dewaters a total of 250,000 300,000 gallons per day of mixed primary and waste activated sludge (biosolids). Of the total flow to the dewatering presses, 80% is from the brewery and the remaining 20% from a nearby municipal wastewater treatment plant. Historically, the brewery fed sodium permanganate ahead of the belt filter press in an effort to reduce H2S odors in and around the biosolids dewatering area. A second permanganate dosing point of was added in 2021 to address the continued odor complaints. Later in 2021, both permanganate injection points were decommissioned due to operational concerns. Permanganate was also suspected of contributing to elevated manganese levels at the effluent due to release of manganese in the filtrate. In early 2022, the brewery WWTP embarked on a 90-day field trial of Peroxide Regenerated Iron Technology (PRI-TECH ®) to address H2S odors generated in the biosolids dewatering facility and also eliminate a source of manganese in the final effluent. For H2S control, PRI-TECH ® functions in two ways: 1) Direct oxidation of H2S by hydrogen peroxide (H2O2) and 2) regeneration of bound iron (e.g, FeS) in-situ, yielding either free ferrous (Fe2+) or ferric (Fe3+) iron and colloidal sulfur. This regenerated iron is now available to bind additional H2S in the biosolids handling process, functioning the same as if fresh iron salts were being added. Pre-trial laboratory testing showed that there were already significant levels of total available iron present in the brewery biosolids (15 25 mg/L total Fe). This equates to 35 40 lbs. per day of iron that was available for regeneration. In this case, the iron needed for PRI-TECH ® was already present in the biosolids and could be used for the benefit of H2S control in the belt filter press area. For the PRI-TECH ® trial, hydrogen peroxide was fed into the combined biosolids line upstream of the belt filter presses to oxidize H2S and regenerate free iron (Fe+2, Fe+3). Baseline (untreated) H2S levels at the belt press ranged from 5 90 ppm with an average above 10 ppm. The brewery safety committee set the H2S compliance target below an average of 10 ppm during dewatering operations to ensure worker safety and to reduce complaints from surrounding neighborhoods. Trial results showed that PRI-TECH ® reduced the sulfide levels by >95% with operational vapor level averages <1ppm inside the belt filter press room. Operations noticed a substantial reduction in local and personal H2S alarms (alarm at 10 ppm) in and around the dewatering building, local odor complaints also decreased, and there were no effluent manganese violations since beginning the PRI-TECH ® program, supporting compliance with metal discharge limits. Based on the successful trial results, the brewery WWTP will continue utilizing PRI-TECH ® to maintain effective H2S control in the dewatering facility to ensure worker safety and maintain effective H2S odor. Future work is planned to further optimize PRI-TECH ® program, with additional investigation into the improvement in critical metals reduction.

WSSC WATER is nearing completion of the Bio-Energy project to thermally hydrolyze and anaerobically digest all biosolids from their five Water Resource Recovery Facilities (WRRFs) at a centralized facility to produce a Class A biosolids. As part of this project, thermal hydrolysis pretreatment (THP) and mesophilic anaerobic digesters are being constructed at the Piscataway WRRF to provide the necessary stabilization to meet regulatory requirements as well as produce valuable digester gas, which will be converted to renewable natural gas (RNG) suitable for pipeline injection. See Figure 1 for an overall process schematic. The Bio-Energy project will fundamentally change how WSSC WATER manages biosolids, allowing a focus on long-term sustainable end products with a Class A dewatered cake biosolids, and RNG suitable for pipeline injection and use as vehicle fuel. The project will reduce the greenhouse gas emissions and result in significant operational cost savings. But with these benefits comes one of the biggest challenges of the Bio-Energy Project to treat the additional nutrient recycle loads that will be generated from sludge imported from the other WRFs and increased even more by THP and anaerobic digestion. Total nitrogen recycle loads from the Bio-Energy Project must be limited to ensure the Piscataway WRRF can maintain compliance with effluent discharge limits. A two reactor ANITATM Mox sidestream treatment process will startup concurrent with the digestion process to treat high ammonia filtrate from the Bio-Energy dewatering process. Managing filtrate generation in coordination with startup of both the Digester and Sidestream processes is essential to maintaining process compliance at Piscataway WRRF. Figures 2 and 3 present digester and sidestream treatment startup graphs. This presentation discusses the integrated startup plan for anaerobic digestion and sidestream deammonification at the Piscataway WRRF to meet multiple goals: - Stable startup of both biological systems, minimizing potential for digester souring, biological washout, etc. - Limiting nitrogen recycle to Piscataway WRRF - Expediting the commissioning schedule as much as practical to allow WSSC WATER to reap the benefits from this facility as soon as possible. Phase 1 Preparation and Seeding Phase 1 involves preparation and biological seeding of both digestion and sidestream deammonification, initially with one digester and one reactor. - Digester 1 will be partially filled with disinfected utility water to a minimum level to initiate pump mixing. The headspace will be purged with nitrogen to prevent an explosive atmosphere as methane concentrations increase. Steam will be used to bring the water to the mesophilic temperature range. Then liquid seed sludge will be imported from the DC Water Blue Plains Advanced Wastewater Treatment Plant (WWTP), which is thermally hydrolyzed and Class A. The digester is now ready to receive hydrolyzed sludge from the Bio-Energy THP process. - Sidestream deammonification has a similar preparation process. The first treatment reactor will be mostly filled with virgin media. Process flow from the WRRF will be introduced to the reactor to condition the media and promote biological attachment. Media conditioning will continue into Phase 2 - Digester Ramp Up to Piscataway Load. Once conditioning is complete, media with annamox biology from an operating ANITATM Mox process will be introduced to the reactor. The sidestream deammonification process is now ready to begin receiving filtrate. Phase 2 Digester Ramp Up to Piscataway Load Indigenous sludge from the Piscataway WRRF will be thickened, screened and dewatered prior to THP. THP throughput will be increased from approximately 4 dry tons/day (dtpd) up to the full Piscataway load, approximately 16 dtpd over approximately 30 days. During this ramp up, the ratio of volatile solids feed to volatile solids under digestion will be kept below 10%. At the end of Phase 2, Digester 1 will reach its normal operating level. Digester 2 will be prepared with water, nitrogen purge and heating before Digester 1 contents are split to Digester 2. Digestate will not be withdrawn during Phase 2 and no filtrate will be sent to the sidestream deammonification process. Phase 3 Sidestream Reactor 1 Startup and Initial Acclimation During Phase 3, digester feed will be held constant at the Piscataway WRRF load (16 dtpd). This period will be used to build the volume under digestion, establish robust mesophilic anerobic digestion microbial communities, and fine-tune operations prior to introduction of imported sludges. Digester withdrawal also begins during Phase 3 to generate filtrate to be used in the Sidestream Deammonification Reactors biological startup. Filtrate sent to the sidestream deammonification process will increase in both concentration and mass loading of ammonia (nitrogen), allowing the annamox bacteria to grow and acclimate to THP filtrate, increasing treatment capacity. During Phase 3, ammonia concentrations in the digesters and filtrate will also be increasing, and will be accounted for when calculating digester withdrawal and filtrate generation and dilution rates into the sidestream reactor. The sidestream process will start in moving bed biofilm reactor (MBBR) mode, with any sludge collected in the clarifier wasted to drain. Phase 4 Sidestream Reactor 1 Acclimation and Reactor 2 Preparation Digester 1 and 2 continue building the volume under digestion, establishing robust mesophilic digestion microbial communities, and fine-tuning operations during the 16 dtpd hold period. The influent ammonia concentration and load will be gradually increased to sidestream reactor 1. Dilution water will be adjusted to meet target feed concentrations and the mass loading will be gradually increased. RAS recycle will be initiated, and the sidestream process will convert from MBBR to integrated fixed-film activated sludge (IFAS) mode. Sidestream Reactor 2 will be prepared for startup, including conditioning of virgin media, introduction of seeded media and phased influent loading. Earlier startup of sidestream Reactor 2 represents an optimization from the initial startup plan, which deferred sidestream reactor 2 startup until reactor 1 was fully acclimated and performance tested. Phase 5 Increased Digester Loadings, Sidestream Reactor 1 Fast Acclimation and Reactor 2 Initial Acclimation After the digester 16 dtpd hold period, sludge will be imported from the four remote WSSC Water WRRFs to increase sludge to the Bio-Energy process. Both digesters will reach normal operating level, and digester withdrawal will be carefully managed to ensure filtrate does not overwhelm the sidestream reactor treatment capacity or exceed total allowable Bio-Energy recycle limits. While there is additional in-tank volume reserved for rapid volume expansion, once the digesters are full feed volume will generally match withdrawal volume, so sidestream treatment capacity must be sufficient to maintain total recycle load below plant limits. Sidestream Reactor 2 seeding and phased influent loading will commence at the conclusion of the Sidestream Reactor 1 slow acclimation period, and follows the same approach as reactor 1. Phase 6 Steady State Digestion and Sidestream Deammonification Phase 6 begins as the Bio-Energy process reaches full sludge load, with all indigenous and remote sludge being treated through THP and digestion. Both digesters will be in steady state operation. As Sidestream Reactors 1 and 2 complete ramp up to full treatment load capacity; startup will be complete, sidestream will be in steady state, and final operation and performance testing will commence. Conclusion Sidestream deammonification is critical to the successful implementation of WSSC Water's Bio-Energy Project, mitigating the impacts of increased nutrient recycle from THP and digestion with imported sludge from WSSC Water's remote WRRFs. The concurrent biological startups of sidestream treatment and digestion must provide stable startup of both biological systems while staying below nutrient recycle targets, all while maintaining an advantageous startup and commissioning schedule. The detailed planning undertaken for this facility allows for all parties to be fully informed and prepared moving into this integrated startup process.

Wastewater treatment plants (WWTPs) were considered to be the biggest microplastics (MPs) source in urban environment (Carr, S.A., Liu, J., Tesoro, A.G., 2016.). Most of MPs in wastewater removed and transferred to sewage sludge (Magnusson, K., Noren, F., 2014.), on the other hand, evidence shown that lager plastic pieces might break apart into small pieces due to the physical or chemical factors in environment (Murphy, F., Ewins, C., Carbonnier, F., Quinn, B., 2016.), some of them will become secondary MPs, therefore, sewage sludge plays the most important role in MPs pollution. In this study, a WWTP in western Japan (we call it as WWTP A here) was the research target. Fig. 1 is the diagram of the sewage sludge treatment system of WWTP A, in this research, all 7 kinds of sludge in WWTP A (marked in red numbers) including primary sludge (raw and thickened), waste activated sludge (raw and thickened), mixed thickened sludge, digested sludge and dewatered sludge were sampled, and all non-fiber MPs larger than 100 μm in those sludges were analyzed. The size, plastic type and color of every MPs were recorded, concentration and annual discharge of MPs were calculated. The sampling will be conducted in some seasons and finally MPs flow in WWTP A was built. Since there are no standard analyzing method of MPs, an analyzing method for sewage sludge was examined and established in this research. Firstly, the pretreatment, if the sludge was in solid state, then dissolved it into milli-Q water until the water content was 96%, after that, all sludge was homogenized by ultrasonic (TOMY, 90% power output of 100 W, 80% duty) for 1 hour. Secondly, every gram (in dry weight) of pretreated sludge was digested by 60 mL of 30% H2O2 in 55 „ƒ for two days, the H2O2 was divided into two parts equally and used in the beginning of each day. After digesting, gravity separation using NaI was used to separate MPs from the solid remains. Finally, micro FTIR (Shimadzu, AIM-9000) was used to analyzing the suspicious MPs. In the summer sample of 2022, Fig. 2(a) shows the MPs concentration in different sludges, MPs concentration was 0.83×103 pcs/kg dry sludge in thickened primary sludge, 2.3×103 pcs/kg dry sludge in thickened waste activated sludge, 1.7×103 pcs/kg dry sludge in mixed thickened sludge, 2.7×103 pcs/kg dry sludge in digested sludge and 3.3×103 pcs/kg dry sludge in dewatered sludge. The MPs concentration in thickened waste activated sludge was much higher than thickened primary sludge, this indicates that more MPs were removed in secondary sedimentation tank in this WWTP, the conclusion here is different in other researches, some report that in some WWTPs, the majority of MPs was removed during primary treatment (Carr et al., 2016; Murphy et al., 2016; Talvitie et al., 2015), while another researcher report that the MPs concentration in primary and secondary treatment was basically the same level (Li et al., 2018.), that's may because the specific treatment method and discharge standard is different between WWTPs. In digesting and dewatering process, the MPs concentration raised 60% and 100% comparing to the mixed thickened sludge, there were two possible explains, one is that lager plastics may break apart into smaller ones due to the physical or microbial factors, the other is the loss of total solid cause the increase of the MPs concentration, combining the MPs amount data in Fig. 2(c), the break apart of MPs might be the major factor since the MPs amount also increased substantially in digesting and dewatering process. Table 1 shows the MPs concentration in this and some other researchers, we can see the MPs concentration varies greatly between WWTPs, the WWTP itself, seasonal reason, analyzing method, target MPs size or other detail cause this difference, overall, the MPs concentration in this Japanese WWTP was in the middle-lower level. Comparing between sludge types, it seems the MPs concentration in primary sludge was the lowest and highly related to the target MPs size, the target MPs size was set smaller, the more MPs would be found, this may indicate the widely existence of smaller size MPs in primary sludge. In waste activated sludge, digested sludge and dewatered sludge, the difference of MPs concentration between WWTPs became even lager and hard to find a pattern, thus it is critical to collect more data to provide some reference for governments to make MPs related policies. Fig. 2(b) shows the particle size of the MPs in different sludges, all MPs found in those sample was smaller than 1,000 μm, the percentage of 100-200 μm MPs was decreasing during the sludge treatment process, those MPs might loss with the separate water during thickening and dewatering. The percentage of 300-400 μm MPs increased significantly, this might because the fermenting bacteria or methanogens are somehow able to decompose MPs partially, it may make lager plastics become fragile and break into 300-400 μm MPs. Fig. 2(c) shows the MPs amount different sludges. The MPs amount in thickened primary sludge was 5.0×109 pcs/y, also much lower than thickened waste activated sludge which was 18.4×109 pcs/y, in mixed thickened sludge the amount was 24.0×109 pcs/y, in digested sludge the amount was 18.6×109 pcs/y and in dewatered sludge the amount was 21.9×109 pcs/y. Different to the concentration, the amount of MPs didn't increased during the sludge treatment process, instead, comparing to the mixed thickened sludge the amount decreased about 23% in digesting and increased 10% in dewatering, the decreased MPs may break apart and become smaller than 100μm thus can not be extract in this research, or possibly drain with the separate water during dewatering. In this research, significant number of MPs was detected in the whole sludge treating process in WWTP A in Japan, evidence also shows that sludge treating process was not able to have a proper treatment of MPs. The final fate of MPs must raise our concern, if those MPs were not treated properly, serious environmental pollution may occur in sludge utilization like compost or agriculture use.

The California Association of Sewerage Agencies Regulatory Workgroup prepared a guidance document in 2022-23 for wastewater agencies who produce biosolids and contract out land application services. The document is aimed at producers of Class B biosolids and it aims to help agencies oversee their contractors in a manner compliant with 40 C.F.R. § 503, i.e. EPA 503 regulations. The purpose of the document is not to address all the elements of an Environmental Management System, nor is it to substitute the best practice guidance from the National Biosolids Partnership. Rather, this document provides a simple distillation of duties retained by a generator of biosolids when the land application of the biosolids is handled by an outside contractor. EPA 503 regulations promote a spirit of cradle-to-grave involvement in biosolids handling on the part of the generator, yet the regulations leave room for interpretation. This is especially complicated for tasks that have been contractually transferred to the biosolids handler and are beyond the operational control of the generator, yet the generator remains responsible in principle. Further complicating interpretation is that EPA 503 does not clearly list generator duties for land application beyond sampling and analysis, leaving the reader to find duties throughout the full legal code. The document describes how the utilities should provide oversight via desktop review and in the field, before, during, and after land application. Aspects of the contractor's operation that can be reviewed via desktop include field permits, trucking routes, crops to be grown, and timing of application. Also, outreach to landowners and local regulators can be conducted in office. It is important to note that EPA 503 promotes communication between the generator and the landowner to ensure that the landowner is aware of the land application practice occurring on their fields. The document describes how a utility can conduct effective site visits to verify that land application practices are consistent with federal, state, and local (county) regulations. Site visits are also encouraged after application to verify the crop being grown at the site. Perhaps most importantly, the guidance describes agronomic loading rates. It provides definitions, calculations, and guidance related to biosolids analysis, soil analysis, field loading, and crop uptake. The guidance addresses how climate and soil type will affect assumptions. The guidance helps agency staff demystify and interpret field reports from a land applier. Finally, while the guidance document describes the limitations of contracts in abdicating a generator's duties, it nevertheless includes example contractual language to help agencies develop strong agreements. In general, the guidance is meant to help both new and experienced agencies monitor their biosolids land application practices. This talk will step through the guidance document and discuss input and nuances for the various recommendations. This talk will be useful to agency staff persons and biosolids contractors alike, as well as consultants and regulators. While the guidance was developed in California, it is applicable to all states.

KEYWORDS Sludge dewatering, data collection, screw press, meta-analysis BACKGROUND Performance estimation for Biosolids dewatering is of great importance for project planning and dewatering system design. Given the cost implications associated with dewatered solids hauling, polymer consumption, and capture rate efficiency, identifying accurate ranges for predicted equipment performance is advantageous to facilities that produce and process biosolids. Equipment manufacturers are able to collect data from existing installations and pilot scale testing for utilization in large scale meta-analysis. This analysis increases predictive capability as it yields insight into how upstream processes and sludge composition influence dewatering performance. Bench scale testing can also be utilized, however should be viewed with more scrutiny, as it cannot exactly replicate onsite performance. METHODS Bench, Pilot, and Full Scale installation testing data was collected from hundreds of facilities across the United States, during a period of time between 2014 and 2022. A Screw Press dewatering device was used on all tests. Figure 1 below shows the number of data points for each type of testing: Bench Scale Testing Pilot Scale Testing Full Scale Installation Testing ~360 ~200 ~100 Table 1: Number of data points for each type of testing conducted in this analysis Figure 1. Dewatered Cake Solids from Screw Press Equipment To assist in the statistical analysis of performance data, multiple descriptive 'tags' were created and assigned to various parameters of the sludge being tested. These tags allowed for the storage, categorization, and comparison of performance data between similar sludges. Each parameter used in the meta-analysis was obtained from a questionnaire filled out by the facility contact, and is one of the 23 following: Sludge Parameter Tags 1. Cake Solids (%) 2. Polymer Dose (lb active/DT) 3. Capture Rate (%) 4. Feed Solids Concentration (%) 5. Throughput (gpm) 6. Solids loading (lb/hr) 7. Machine Size 8. Facility Flow (MGD) 9. Waste Sludge Flow (GPD) 10. Sludge Age (days) 11. Sludge Type (WAS, Primary, Blend) 12. Volatile Solids Ratio (%) 13. Digestion Type (Aerobic, Anaerobic) 14. Total Dissolved Solids (mg/L) 15. Sludge pH 16. Chloride Value (mg/L) 17. Phosphate Value (mg/L) 18. Nitrate/Nitrite (mg/L) 19. Sludge Temp (F) 20. Bench Cake/Bench Polymer Dose (For comparison to field values) 21. Biological Process Type 22. Type of sludge storage (Day tank, Holding tank, Lagoon) 23. Digestion temperature range (Mesophilic, Thermophilic, TPAD, None) Table 2: Sludge Parameter Tags Recorded parameters were tabulated and analyzed using Microsoft Excel, as this provided the easiest means for exporting data collected from online forms. The programming language Visual Basic was utilized as a tool to filter and plot all of the data, allowing for comparison and determination of trends between two different sludge parameters. RESULTS The operator of this analysis tool is able to define X-axis and Y-axis parameters for comparison. Once selected, data points will be plotted along with a trend line to describe the behavior of the data set. Any additional filters applied to the data will further narrow the data set, allowing the operator to view only those data points which fall within a desired range of sludge characteristics. Figure 2. Data Analysis Main Page Further analysis employing the use of standard deviations for each data set allowed for the creation of statistically derived ranges that aid in estimating performance to a more accurate degree than sludge type alone. One such example is shown below in Figure 3, where Cake Solids (%) is compared with Volatile Solids Ratio (%). This search is further refined by only looking at Waste Activated Sludges (no primary component) with Aerobic Digestion. This returns a truncated list that provides a clear relation between Cake Solids and VSS for the sludge type specified. Figure 3. Cake Solids vs. VSS Ratio for Aerobically Digested WAS Sludges Another example of this can be found in Figure 4, which shows a trend of polymer dose compared to feed solids. This is further filtered by looking only at anaerobically digested sludges which fall within the mesophilic temperature range. Figure 4. Polymer Dose vs. Feed Solids for Anaerobically Digested Sludges in the Mesophilic Temperature Range DISCUSSION The tool shown above is useful in making performance determinations and estimations for new and existing projects by leveraging past data from multiple sources. The accuracy of this tool will continue to increase as the data set becomes more robust, meaning that the usefulness of this meta-analysis for project planning will continue to increase. Cooperation between manufacturers, consultants, municipalities, and academia in combination with tools similar to the one described herein has the potential to bridge the gap between dewatering system expectation and actual performance, as each party is able to bring unique contributions to the discussion. The intent of this project was to continue the conversation on ways to create more accurate projections for municipal sludge dewatering performance. Further, this project aimed to explore and qualify the intricacies that are inherent in the municipal wastewater treatment process, and provide a way to identify the factors that can positively or negatively affect dewatering system performance. It should be noted that while this project aimed to be as thorough as possible in terms of data collection and analysis, the study of sludge Dewaterability is ongoing, and as such some factors which influence dewaterability were not included at the time of writing. SIGNIFICANCE/IMPLICATIONS Manufacturers typically have the greatest access to large quantities of data, due to the many projects that they entertain. Through coordinated efforts between all involved parties, a qualitative approach to data analysis can allow for a better understanding of how to estimate performance, especially at new facilities where sludge is not available for testing. Statistical meta-analysis can provide a higher degree of certainty regarding performance expectations as compared to traditional estimations based on sludge type alone.

ABSTRACT British Columbia (BC) is 1.4 times the size of Texas. While only 1% of its land base is native grassland, these areas have been historically prized for homesteading and early agriculture. Today they are mainly used for ranching, but over a century of use has left many BC grasslands in a degraded state. These grasslands support more threatened and endangered species of birds, animals, and vegetation than any other terrestrial biome in the province. The OK Ranch is a 15,000 acre cow-calf operation located in the interior of BC, and was emblematic of these challenges. The upland grasslands of the OK Ranch experienced a decrease in productivity over the last century due to long-term agricultural and grazing practices, now compounded due to climate change. First Nations oral histories tell of tall grasses 'belly high to a horse' flowing with the upland winds, but due to historic homesteading and more recent attempts at cereal production in this dry, high-altitude area, soils were exposed to harsh elements and the natural forage was unable to return to previous production levels. In 2013, SYLVIS partnered with the OK Ranch's landowner to emphasize grassland restoration using biosolids to achieve effective stewardship as well as productivity for the ranch operation. Since that time, SYLVIS and Metro Vancouver, together with several research partners, have sought to understand and quantify the benefits conferred to the site through the careful use of biosolids as a soil amendment tool. This presentation will share the unprecedented understanding of what can happen for a degraded ecosystem when provision of critical soil conditioning supports rehabilitation. Specifically, we will discuss how: -Soils have been protected through the growth and expansion of a thatch layer, and reduction of bare soil and crusting throughout the site. -Grasses have recovered and now grow with vigour, producing up to 400% more biomass, while also being more nutritious for cattle and ungulates. -The changes in biomass and resilience have resulted in significant carbon capture on the landscape, both in short-term annual carbon through above ground biomass, but also in long-term belowground carbon capture and storage in soils and roots. -The improved grass structure has resulted in favorable habitat development for endangered or threatened insects, which in turn support threatened bird species, which has become a major research focus at the OK Ranch through a partnership with the University of British Columbia. -Mammals, large ungulates, and predators appear to spend more time in the grasslands. -The productivity has resulted in increased employment at the OK Ranch, with more cattle and more hands hired to help manage those cattle. -A desktop analysis of climate change mitigation and ultimate benefits to the environment provides a compelling case for the economic, environmental and societal value of grasslands restoration. The OK Ranch grasslands restoration project is more than just land application of biosolids. It demonstrates the layers of co-benefits provided through the restoration of semi-arid grasslands of not just soil improvement, but of carbon capture, habitat recovery, and economic development. . The presentation will conclude with a discussion of what levels of awareness and information sharing might be required, and what innovative strategies are available to increase uptake of beneficial use messages to achieve this kind of scale for grassland restoration in North America.

INTRODUCTION Thermal hydrolysis pretreatment (THP) holds promise to intensify the solid handling capacity of mesophilic anaerobic digesters (AD) by improving the sludge biodegradability, pumpability, dewaterability, and biosafety. Typically, the digester feedstock total solids concentration (TS) can be doubled from 5 to 10%, and the solids retention time (SRT) can be halved from 30 to 15 days after THP is installed, which directly enables existing AD to quadruple the loading rate capacity (Higgins et al., 2017 and Walley, 2007). Although the feedstock TS is hard to further increase due to its viscosity limit and the potential to cause free ammonia inhibition, the digester SRT has been believed to have room for further intensification (Zhang et al., 2022 and Xue et al., 2015). However, to what extent the SRTs can be further shortened without deteriorating the expected digester performance needs to be explored. To this end, a pilot study was conducted in Arlington Water Pollution Control Plant (AWPCP) to understand the impact of further reducing SRT from 15 to 12.5 days and then to 10 days on AD. This study is anticipated to provide engineering guidance for other utilities that consider pursuing process intensification of THP-AD systems. METHODS AND MATERIALS As shown in the process flow diagram in Figure 1, a pilot-scale CAMBITM THP unit shown in Figure 2 was operated at a steam pressure of 6 Barr (equivalent to 165 oC) for 30 minutes to pretreat municipal sludge in preparation for subsequent ADs. Three 10-liter, mechanically mixed ADs shown in Figure 3a were operated in parallel with temperature maintained at 36.5 ± 0.3 oC and SRTs controlled at 10, 12.5, and 15 days, respectively, by manipulating the daily sludge exchange volume. The system temperature control configuration is illustrated in Figure 3b. All ADs were inoculated with the effluent from a full-scale THP-AD system in DCWater. AWPCP cake consists of primary sludge (PS) and wasted activated sludge (WAS) blended at a dry mass ratio of 3:2. The cake was diluted with distilled water or THP steam in each step of the flow diagram according to the TS levels shown in Figure 1. This AD system was continuously operated for 273 days from 6/3/2021 to 3/2/2022. RESULTS AND DISCUSSION AD Startup All three ADs were started with the same SRTs of 30 days (Figure 4). Their SRTs were then step-wise decreased by 0.5 days per day until reaching a 16-day SRT at which all three reactors were stabilized for 1.5 months to prevent reactor failure due to high volatile fatty acid (VFA) concentration. After that, the SRTs were further reduced to 15 days and stabilized for another 1.5 months. In the end, the SRTs of two ADs were finally reduced to 12.5 and 10 days, respectively, at a pace of 0.5 days every other day, and all three ADs were operated without any SRT change thereafter for the remaining 152 days of operation. Effect of SRTs on solids reduction and methane yield As shown in Figure 5a, the steady-state volatile solids reductions (VSRs) were measured to be almost linearly correlated to the SRTs, indicating that shortening SRTs played a major impact on the sludge hydrolysis rate. This is because shortening SRTs from 15 days to 12.5 days and then to 10 days has reduced VSR from 60.7% to 57.5% and then to 53.6%, respectively. In contrast, the methane yield did not show a clear dependence on the SRTs even though the AD with 15-day SRT produced 7% more methane than those with 10-day and 12.5-day SRTs (Figure 5b). This asynchronization between VSR and methane yield suggests that it was the methanogenesis but not hydrolysis limiting the methane production (Figure 5a and 5b) probably due to the THP enhancement on hydrolysis. This can be seen from the substantial reduction of sludge particle size before and after THP as well as AD as shown in Figure 5c. It is noteworthy that SRTs did not cause any significant impact on the particle size distribution of digested sludge (Figure 5c). Effect of SRTs on COD, nitrogen, and phosphorus turnover The total chemical oxygen demand (tCOD) was slightly decreased after THP probably due to the loss of some volatile organics during sludge transfer to AD (Figure 6a). A linear SRT effect on tCOD can be seen in Figure 6a, which is consistent with the trend of VSR in Figure 4a. In contrast, total kjeldahl nitrogen (TKN) in Figure 6b remained unchanged during THP but slightly decreased in ADs with increasing SRT probably due to the volatilization of ammonia nitrogen at a higher bulk concentration as shown in Figure 6d regarding the total ammonia nitrogen (TAN). The soluble COD (sCOD), on the other hand, was significantly increased after THP, evidencing the effectiveness of thermal hydrolysis (Figure 6c). Figure 6c showed that about 60% of sCOD was removed in the form of methane in ADs. The levels of residual sCOD, especially the 1.5 µm filtered, appeared to be inversely related to the SRTs, corroborating the rate-limiting step is methanogenesis inferred from Figure 5a (Figure 6c). It is interesting to see that the orthophosphate (OP) released into the bulk solution was mainly affected by THP but not by AD SRTs probably due to the convolution between hydrolysis and precipitation in ADs (Figure 6e). Effect of SRTs on sludge rheology and dewaterability The sludge rheology was mainly influenced by the THP instead of SRTs. This can be seen from the dramatic drop of apparent viscosity from 3.6*105 millipascal-second (mPas) to 2.8*105 mPas measured at a shear rate of 0.021 s-1 after THP, while only slight changes were observed at different SRTs (Figure 7a). Nevertheless, all of the sludge showed non-Newtonian, shear thinning behavior which is in consensus with the literature (Higgins et al., 2017). The sludge dewaterability as indicated by the capillary suction time (CST) showed that the sludge dewaterability became worse after AD which is expected based on the literature (Novak et al., 2003). However, SRTs did not show any significant impact on the CST, suggesting that the sludge dewaterability should remain the same when SRTs were reduced from 15 days to 10 days. CONCLUSIONS This study revealed that shortening SRTs from 15 to 10 days reduced VSR from 60.7% to 53.6%; however, other key AD performance parameters such as methane yield and sludge properties in terms of rheology and dewaterability largely remained unchanged.

Liquid biosolids land application programs have successfully operated in North America for decades. Land application of biosolids is an economical way for farmers to improve crop production and soil health while reducing greenhouse gas emissions and the landfilling of biosolids. However, with growing populations and increasing wet weather events, some programs have more recently experienced operational challenges surrounding hauling, land application, and inadequate storage. This has encouraged some programs to explore alternatives to their traditional biosolids management practices. Lystek THP is a biosolids management solution that uses thermal hydrolysis to transform biosolids and residuals into a concentrated and pathogen free liquid fertilizer product. It is a cost-effective way to extend liquid storage and reduce management stresses in facilities with existing dilute liquid land application programs. The patented process produces a concentrated (13-16% solids) EPA Class A biosolids fertilizer, LysteGro. This concentrated liquid fertilizer is applied via sub-surface injection, ensuring cleanliness when compared to traditional surface methods. Injection application increases soil contact, ensuring efficient nutrient use, and mitigation of run-off potential. The liquid product also allows for efficient loading and off-loading, as well as odor mitigation at the plant and throughout transportation. Notably, the concentrated liquid biosolids fertilizer contains added potassium (K), a key nutrient that is present in only very low quantities in other biosolids. The addition of potassium ensures the product can be used as a full replacement for conventional mineral fertilizers - providing significant value to the farmer. Benefits of this biosolids fertilizer application are realized over multiple years due to the slow-release nature of the nutrients in the product and improvements in soil health. Micronutrients, including zinc and copper, as well as macronutrients, including calcium and sulfur, important for crop growth are inherent in biosolids. This provides farmers with an accessible and sustainable option for these nutrients that would typically be expensive to purchase in the mineral fertilizer form. The addition of organic matter to soils helps improve overall soil health - including improved water holding capacity, soil structure and tilth, increased microbial activity, as well as increased resilience to severe weather conditions. We will discuss two relevant case studies: St. Cloud, Minnesota, and the South Huron Valley Utility Authority (SHUVA) in Brownstown, Michigan and the operational improvements they have realized as a result of a reducing residual biosolids volumes by implementing a concentrated Class A liquid biosolids fertilizer program. The City of St. Cloud's Nutrient, Energy, and Water Recovery Facility was looking to pursue a Class A treatment technology as part of its Resource Recovery and Energy Efficiency master plan to prepare for possible future regulatory changes. Facing storage capacity issues with their previous dilute liquid Class B program, they were also looking for solutions that could reduce their biosolids volume. St. Cloud's Class B biosolids application program had been successfully managed and operated for many years by City staff, with a receptive farming community for biosolids. Lystek was selected by the City of St. Cloud to supply the Class A biosolids treatment technology. The system became operational in the plant by September 2018 and St. Cloud has continued to operate their successful land application program using their existing infrastructure and equipment, without the addition of any new buildings or biosolids storage. They have seen a dramatic 70% reduction in their biosolids volumes and associated trucking, correspondingly reducing their biosolids program's transport greenhouse gas emissions by 70%. The program itself has also become easier to manage as the City of St. Cloud saw decreases of 85% in their overtime hours associated with land application. The estimated cost savings of producing and managing a concentrated liquid fertilizer at St. Cloud are approximately $12 million over the 20-year life cycle when compared to alternative solutions. The South Huron Valley Utility Authority (SHVUA) was seeking a solution to manage their dilute liquid biosolids program at their wastewater treatment plant serving a population of 90,000. The existing low-solids, lime stabilized Class B biosolids program was severely limited by insufficient winter storage and the WWTP was required to implement a costly contingency option of dewatering and hauling to landfill. Switching to a concentrated liquid fertilizer program has provided the SHVUA WWTP with a solution to reduce biosolids volumes by over 50%, effectively doubling that plant's storage capacity, while also producing a Class A biosolids fertilizer for local agricultural use. This change has ensured operational security and eliminated the need to dispose of 'excess' biosolids in landfills, allowing the Authority's resource recovery program to advance. Additionally, the plant was able to eliminate the use of lime stabilization and the associated chemical costs, as well as necessary storage clean out activities. The Lystek THP module processing footprint was small enough that it could be installed in an existing building with unused space, maximizing the use of existing infrastructure. Concentrated liquid biosolids fertilizer programs allow for efficient biosolids management through integration with conventional wastewater treatment plant equipment and processes. This program can greatly reduce a WWTPs volume of biosolids and required storage infrastructure, remove the need for complex management systems and infrastructure, and decrease trucking costs, all while providing a desirable fertilizer product.

Enormous quantities of pharmaceutical and personal care products (PPCPs) are used worldwide every day. Significant amounts of these PPCPs reach wastewater treatment plants (WWTP) where they are primarily concentrated within biosolids in the solids treatment train and are not completely treated (McClellan et.al., 2001). Approximately 60% of the biosolids generated in the United States (US) are land applied. As a result, the US Environmental Protection Agency (EPA) has recognized the need to evaluate the occurrence, fate, and potential risk of unregulated pollutants in biosolids considering that land-applied biosolids may result in introduction of these pollutants to the environment via transport to soils, surface, and ground waters, as well as edible crops and animal products (Gerba et. Al., 2009, US EPA 1999). The 40 CFR Part 503 Sludge Rule provide us confidence and a framework on how to best manage risks from unregulated emerging pollutants in biosolids (National Academic Press, 2002). Additionally, Section 405(d) of the Clean Water Act (CWA) requires EPA to periodically review sewage sludge regulations to identify any additional pollutants that may occur in biosolids, and to set regulations if sufficient scientific evidence shows they may adversely impact human health or the environment. The emergence of analytical methods to measure increasingly lower concentrations of pollutants, combined with new data on the potential for human health and environ-mental impacts, requires the EPA to evaluate these newly detected compounds. With the universe of compounds that must be considered under this paradigm, the EPA is working to modernize, standardize, and streamline the risk assessment process for risk assessment of these constituents of emerging concern in biosolids. The EPA's Office of Water has developed a draft Biosolids Chemical Risk Assessment and Biosolids Screening Tool (BST) and a User's Guide to identify pollutants, pathways, and receptors of greatest interest and inform decisions regarding the need for refined risk assessment of land-applied biosolids, which is currently under review by a Scientific Advisory Board. Additional information can be obtained on EPA's website. In context of this issue, the EPA Recently funded nearly $6M to four institutions for research to support states, municipalities, and utilities in determining the potential risk from pollutants found in biosolids. Results from this research will be used to inform the development of standards and policies for biosolids management. One of the four funded projects, being led by Michigan State University, Colorado State University, University of Georgia Research Foundation, and the Great Lakes Water Authority is focused on PPCPs and PFAS as representative pseudo-persistent emerging contaminants (due to continuous discharge despite relatively rapid dissipation in soils). The teams aim to improve knowledge of occurrence, transport, fate, plant uptake, livestock, and human exposure to pollutants in land-based biosolids. The study will generate scientific information that will be important in risk management and in informing beneficial use management strategies. As an extension to this interdisciplinary, multi-institutional, multi-state, and university-industry collaborative partnership, including an initial 12 wastewater utility partners, the team has funded additional sampling to expand the study to 28 individual WRRF sites in North America (Figure 1). The objective of this surveillance study is to understand the range of concentrations of these compounds in biosolids, and to determine correlations of concentrations as a function of treatment processes. Participating Utilities were contacted in the summer of 2022 to complete a 102-question survey about their operations and process trains. After analyzing the survey data, samples were collected. Currently samples collected from the 24 WWTPs and remaining will be collected by end of 2022. Samples were collected as solids entered the solids treatment train (e.g., blended primary and waste activate sludge entering the anaerobic digesters) and at the compliance point of the stabilized biosolids product leaving the WWTP, regardless of end use or disposal method. WWTPs where the solids treatment trains were complex or had multiple outputs, more than two samples were collected and assessed. The samples were analyzed for 57 PPCPs (Table 1) by SGS AXYS according to method MLA-075 (EPA 1694). In addition to PPCP analyses, general characterization of the sludge was also conducted which included: pH, alkalinity, total solids, total volatile solids, and chemical oxygen demand (COD) and other parameters. To maintain anonymity, with respect to potentially sensitive data, WWTPs are not named, and data is presented to analytical laboratories and universities according to facility codes. Results from this surveillance study will be presented to provide an initial overview of the range of PPCP concentrations that enter solids treatment processes, percentage treated/removed by the various solids treatment trains, and the final concentration present in the biosolids. The data is invaluable in supporting an understanding of what utilities throughout North America could expect and can support an understanding of how PPCPs are removed through biosolids treatment processes, which can support decisions on management practices and strategies for biosolids disposal/beneficial reuse.

INTRODUCTION Despite the fact that MPs can be removed from wastewater with an efficiency of up to 90 %, still 105108 microplastics (MPs) are released from WWTPs each day (HatinoÄŸlu & Sanin, 2021). Indeed, more than 90% of the removed MPs accumulate in sludge during treatment (Okoffo et al., 2019) reaching an abundance varying from 510 to 495,000 MP particles/g DS (HatinoÄŸlu & Sanin, 2021). Studies reveal that MPs have harmful impacts on organisms; they may act as a vector of hazardous pollutants such as pharmaceuticals and heavy metals with an absorption mechanism onto their surfaces. Moreover, they provide sustainable surfaces for pathogens to colonize and form biofilm. Even though pathogens can be removed by WWTPs to a great extent, MPs can offer a safe environment for them to survive during the treatment process. MPs themselves, together with the hazardous chemicals and pathogens they can accumulate on their surfaces, pose a new concern for the land application of biosolids. Anaerobic digestion (AD) is a sustainable stabilization system with renewable energy generation and good-quality biosolids production for land application. Thermophilic digestion (TAD) is well known to be more effective in stabilization compared to mesophilic AD (MAD) due to its effective pathogen inactivation and Class A biosolids generation. Recent studies have shown that the presence of MPs can affect AD, and in addition, MPs themselves seem to be affected during the process. Yet, all these studies investigating MPs in AD are conducted under mesophilic conditions. TAD has not been investigated so far to reveal the fate and effect of MPs during the process. Polyamide (PA) (nylon) with amide groups (-CO-NH-) having the strength and fatigue resistance is one of most commonly encountered type of MP in sludge (El Hayany et al., 2022). Its high abundance and leaking potential of its monomer caprolactam (CPL) during MAD (Chen et al. 2021) creates interest for PA6. This study aims to comparatively investigate the effect of PA6 on methane production with MAD and TAD while evaluating this MPs' fate during these processes. This work is unique for identifying the behavior of MPs in TAD and specifically evaluating the fate and effects of PA6 comparatively in MAD and TAD processes. MATERIAL & METHOD For the simulation of MAD and TAD, biochemical methane potential (BMP) test was conducted at 35oC and 55oC, respectively. Waste activated sludge (WAS) (substrate) and anaerobically digested sludge (ADS) (inoculum) were sampled from a conventional WWTP designed for a population equivalent of 4 million with a capacity of 765,000 m3/day. The seed was used as sampled for MAD BMPs but was acclimated for the TAD study. As PA6, a fishline with a diameter of 0.5 mm was cut into sizes in the 425-500 µm range and used. Each mesophilic and thermophilic BMP tests had 13 sets of triplicate reactors comprising biotic, abiotic control and seed control groups. Each biotic and abiotic set included six different PA6 doses in reactors, 0, 10, 30, 60, 100, and 200 MPs/g TS. Reactor TS values were adjusted to 2% with an F/M of 1 (g VS of WAS/g VSS of seed). All reactors were purged with 99% nitrogen gas, and were incubated for 60 days. Biogas volume was measured routinely with water displacement and its composition was determined by Gas Chromatography (GC) with a thermal conductivity detector (TCD). Solids were measured using Standard Methods and COD was measured with the US EPA-approved digestion method. Mass, size, and morphology of PA6 before and after digestion were evaluated with scanning electron microscope (SEM), fourier transform infrared (FTIR) spectroscopy, and differential scanning calorimetry (DSC) to comparatively assess the changes in MPs during digestion. RESULTS & DISCUSSION The cumulative methane productions of MAD and TAD reactors are shown in Figure 1 and Figure 2, respectively. In both groups, methane production started immediately and increased steadily as time went on. In the thermophilic reactors different than the mesophilic reactors, methane volume increased in two distinct steps; second step coming about 10 days after the first. In both mesophilic and thermophilic reactors, the highest methane production has been observed in the reactors containing the highest dose (200 PA6/g TS), with the lowest dose, 10 PA6/g TS, following. However, for the mesophilic group, reactors with all other doses of PA6 produced lower methane than the control set (R0M). Even though one-way ANOVA test showed a significant difference between the sets (p<0.05), a further test of post hoc (TUKEY test) demonstrated that the significant difference was only between the R30M and R200M sets. As a consequence, when compared to the control set, PA6 addition seemed to have no effect on methane production. In TAD reactors however, while no pattern between dose and methane production is seen (Figure 2), the outstanding results reveal that all PA6-added reactors produced significantly higher methane than the control set (R0T), as validated by One-Way ANOVA results (p<0.05). Additionally, the post hoc test (TUKEY test) found that except R100T, all the PA6 added sets have significantly different methane production compared to the control set (R0T), indicating PA6 affected methane production positively in TAD. This is thought to be due to leaching of monomer CPL. Chen et al., (2021) claims that CPL attaches to enzyme molecules, changing the enzyme's active site and other conformations, increasing the enzyme's affinity for the substrate and catalytic activity. The distinct second step of increase in methane production may hint the leaching of CPL providing additional affinity for enzyme-substrate system, which is currently under investigation. SEM images were captured to examine the changes in the shape and surface of PA6 during the MAD and TAD processes. Figure 3 depicts the SEM results of biotic and abiotic controls from the mesophilic BMP test. Images exhibit minor changes on the borders of PA6 after digestion. In order to better understand the changes experienced by PA6, FTIR and DSC analyses for both mesophilic and thermophilic reactors are currently underway. ACKNOWLEDGEMENT This study is supported by METU-BAP with a grant number of BAP-GAP-311-2021-10613.

INTRODUCTION Mechanical dewatering of solids before or after digestion or stabilization processes is typically employed by utilities to reduce the water content of their solids in order to decrease transport costs. Prior to the mechanical dewatering process (such as centrifuges or belt filter presses) the solids need to be flocculated to increase the particle size and strength to make the solids amenable to mechanical dewatering such that the water drains easily through the particles and the particles can withstand the shear during dewatering. The process of preparing the solids for dewatering is typically referred to as 'conditioning'. The vast majority of WRRFs use high molecular weight, cationic polymers to condition their solids. Unfortunately, polymer costs have risen dramatically in recent years and these costs have become significant. In some cases, the availability of polymer has also become limited due to supply chain issues. As a result, WRRFs need approaches to reduce polymer demand for their conditioning process while not sacrificing performance in terms of cake solids and capture of solids. One approach to reducing polymer demand is through a multi-point polymer addition scheme in which a smaller dose is added at one point in the solids pipeline, this dose is allowed to mix, and then additional dosages are added downstream to fully condition the solids. This approach has been shown to reduce overall polymer demand, although the effects on cake solids and capture have not been well studied. The objectives of this research are to evaluate the impact of multi-point polymer conditioning on the overall polymer demand as well as cake solids and capture. METHODS AND MATERIALS The solids used for this testing were from a conventional, mesophilic anaerobic digester that was a mix of primary and waste activated sludges. To evaluate multi-point addition of polymer, a laboratory-based method of dewatering was employed. The details of this method have been described by Ngwenya et al. (2017). Figure 1 shows an overview of this method. Briefly, the method utilized controlled mixing to impart the same velocity gradient, G, for the same amount of time during the conditioning step since the shear during mixing has been shown to impact polymer demand. The extent of conditioning or flocculation is assessed using the capillary suction time (CST) and the optimum polymer dose is taken as the polymer dose with the lowest CST. After finding the optimum polymer dose, the solids are then dewatering using the centrifuge cup method, again, all parameters are held constant such that the only variable would be the characteristics of the solids. To evaluate the multi-point polymer addition versus traditional approach with all the polymer addition at one location, the solids were conditioned using a constant mixing time and all the polymer dose added at one time and the optimum polymer dose was determined using the CST versus polymer dose curve. To compare this conventional approach with multi-point addition, the dosage was broken up, typically applying half the original dosage at time equals zero, and then the additional dosages were added at different time intervals. In all cases, the total time of mixing remained constant such that the shear did not vary during the experiments. An example timeline for the multi-point addition experiments is shown in Figure 2. At the optimum dosage, the solids were then dewatered to determine the impact on cake solids and the filtrate solids were also measured to assess capture. The full details of the method will be described in the paper. RESULTS AND DISCUSSION The CST versus polymer dose curves for single, two- and three-point addition are shown in Figure 3. The curves show the typical U-shape in that the CST decreases as the polymer dose increase, reaches a minimum, and then begins to increase due to polymer overdosing. Using the minimum CST as a the optimum dosage, two point addition reduced the polymer demand by about 20% relative to the control, while three point addition reduced the polymer demand by about 30% which would result in substantial cost savings. The box plot of cake solids for these three polymer addition schemes is shown Figure 5. The one- and two-point addition had the same cake solids, around 19%, while the three-point addition had a slightly lower cake solids, around 18%. Interestingly, the cake solids were generally not impacted much using multi-point addition as long as good mixing intensity was used. In cases where less intense mixing was used, the multipoint addition decreased the polymer dose, but also resulted in a greater reduction in the cake solids. These various results will be discussed in more detail in the full paper, along with an overall economic analysis to show the tradeoffs between reducing polymer demand versus the impacts in cake solids. SUMMARY The results showed that significant polymer reduction can be achieved with multi-point addition schemes without sacrificing cake solids as long as mixing was sufficient. This approach could be a simple approach that WRRFs could implement to reduce costs by reducing their polymer demand while not sacrificing cake solids.