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Background Wastewater Treatment Plants (WWTPs) in South Carolina and Georgia have been historically dependent on landfill disposal for the management of the wastewater solids generated through their respective treatment processes. In Georgia and South Carolina nearly 65% of wastewater solids are sent to landfill. In recent years, landfills in both states have undergone policy changes that include steep increases in tipping fees for wastewater solids and a reduction in wet waste acceptance. The reduction of wet waste acceptance limits the percent wet waste (>40% moisture) accepted into landfills. In Georgia, landfills are required to develop a detailed Sludge Management Plan (SMP) if they accept more than a 5% wet waste to 95% Municipal Solid Waste (MSW) ratio. The changing landscape surrounding landfill disposal creates significant challenges for WWTPs in both states. The uncertainties resulting from these changes have served as the impetus for four WWTPs (two in Georgia and two in South Carolina) to evaluate new biosolids management technologies, beneficial use markets, and management methods. Objective Four utilities located in Gainesville, GA, Douglasville, GA, Beaufort, SC, and East Richland, SC underwent Biosolids Regulatory and Market Assessments for their respective WWTPs. The assessment worked to identify opportunities and challenges resulting from state regulations, local markets, and corresponding economics, associated with managing various biosolids products under consideration. Comprehensively, the Regulatory and Market Assessments for all of the utilities serve as a guide to the biosolids beneficial use and disposal outlets and management methods to achieve the following three objectives. 1. Identify permitting pathway for several biosolids products and management methods in Georgia and South Carolina; 2. Identify beneficial use and disposal outlets in the region for the respective baseline products generated by each WWTP; 3. Identify beneficial use and disposal outlets in the region for proposed products; and 4. Define market details including market capacity, storage requirements, and revenues and expenses associated with product management. Methodology The Biosolids Regulatory Assessments included a detailed review of existing Federal and state biosolids beneficial use and disposal regulations, as well as future regulatory federal and state regulatory considerations. Encompassed in the Market Assessment for each utility, the baseline solids management program was examined to understand existing practices and costs associated with solids disposal. Information about the local market preferences and demand for the biosolids products being considered for each utility was gathered through market research and interviews with potential market outlets. Collected data was used to identify the opportunities, challenges, and outside-the-gate program expenses (those expenses associated with product management only) associated with each market/product combination. The data from each utility was further analyzed to develop an idea of the current biosolids beneficial use and disposal trends relating to the management of several biosolids products in both South Carolina and Georgia. Four main products were evaluated including Class B digested cake, Class B and A/EQ alkaline stabilized cake, Class A/EQ compost, and Class A/EQ thermally dried granules. Findings and Current Status Assessment findings reveal that the development of beneficial use programs, both self-managed programs (SMP) and Third-Party Contractor (TPC) managed programs are available and viable in South Carolina and Georgia. Listed below are the main recommendations and findings that were consistent for each Market Assessment: 1. High Level of Interest in Class A/EQ Thermally Dried Granules: In each Market Assessment, thermally dried granules scored higher than other products due to the high level of interest noted in outlet surveys as well as the increased product flexibility within several different markets. Although interest level is high, many interested market outlets require a high-quality product, which is typically generated from rotary drum dryers. 2. Availability of Off-Site Stabilization Facilities: Off-site stabilization facilities are currently available with more coming online in the coming years. The majority of stabilization facilities in Georgia and South Carolina are composting facilities which product Class A/EQ compost for several markets. 3. On-Site Storage Requirement: 3 months of on-site storage is highly recommended, regardless of which market/product combination is pursued. The increase of on-site storage presents each utility with increased flexibility and resiliency. A summary of the selected products, most promising markets, relative outside-the-gate costs, opportunities, and considerations are summarized in Table 1. Furthermore, a summary of the regulatory considerations for Georgia and South Carolina can be found in Table 2. The Market Assessment findings indicate the current market conditions are strongly favorable for beneficial use of Class A/EQ compost and dried granule biosolids products. The presentation will further discuss the relative outside-the-gate costs associated with the management of each product as well as growing trends relating to the beneficial use of biosolids in this region.

Executive Summary: South San Francisco-San Bruno Water Quality Control Plant (WQCP) incorporated high-solids digestion to cost-effectively provide necessary capacity and avoid the need to build additional digester tanks. Following third-party validation of healthy digester operations in high-solids conditions, the WQCP advanced a food waste co-digestion pilot in partnership with a nearby waste management authority. The pilot demonstrated significant increase in biogas production, without negative impact to digester health. The initiative not only sets the stage for the WQCP to advance energy-neutrality but also supports achievement of state-level organic waste diversion mandates in California to support greenhouse gas reductions. Background: The WQCP identified a need to rebuild the plant's three existing digesters due to seismic concerns and built additional AD to meet future load growth. While capital planning initially called for new construction of five (5) digesters total, Carollo Engineers conducted an alternatives analysis considering high-solids digestion to more cost-effectively achieve the required digester capacity. Carollo evaluated a scenario pairing two (2) conventional AD with one (1) high solids digester employing Anaergia's Omnivore high-solids digestion platform. Anaergia's two-part Omnivore AD platform triples capacity of existing digesters to maximize existing WRRF infrastructure and provide redundancy. Anaergia's sludge screw thickener (SST) (Fig. 1) recuperatively thickens digestate to decouple SRT from HRT, allowing digesters to operate at significantly higher solids content. By separating water from digestate, excess water is removed and returned to plant headworks for additional treatment and/or nutrient recovery, while thickened solids (typically 12% TS) are returned to the digester (Fig. 2). Digestate is therefore thickened up to three-fold (6-8% TS) thus tripling F:M ratio and enabling organic loading rates up to 0.33 lb-VS/ft3/day. By decoupling SRT from HRT, Omnivore ensures SRT well over 15 days required for regulatory compliance and stable digester operation. To ensure proper mixing in higher solids conditions, Omnivore employs Anaergia's high-torque submersible propeller mixers (Fig. 3). These high-efficiency mixers are designed to effectively mix high viscosities that result from thickening digestate and resist ragging. By applying mixing energy directly to digestate, Omnivore mixing achieves a high standard of mixing performance, over 90% of the digester volume continuously mixed above critical velocity (0.3 ft/s) ensuring maximum volatile solids destruction, biogas production, avoiding settling of grit, and homogeneity de-risking upset events such as rapid rise. The Carollo evaluation indicated that the proposed configuration leveraging high-solids digestion would deliver equivalent digester capacity to the originally planned five (5) tanks. Further, lifecycle cost analysis confirmed that the high-solids alternative would not only achieve CAPEX savings but OPEX savings, resulting in approximately 10% overall savings over the project life. OPEX savings to the WQCP primarily result from improved mixer energy efficiency and reduced polymer consumption associated with dewatering. Application: In late 2020, construction was completed to retrofit Digester 1 (0.83 MG) with the Anaergia Omnivore high-solids digestion (HSD) system. The technology package included one skid-mounted sludge screw thickener (SST) for recuperative thickening, three high-solids submersible PSM digester mixers, three mixer service boxes, and all ancillary equipment for a complete Omnivore system. Existing mixers were removed from Dig. 1 and replaced with new Anaergia propeller mixers. Mixer selection was validated and informed by computational fluid dynamic (CFD) modelling, the results of which are summarized in Tables 1-4. The model demonstrated low energy demand, improved tank mixing, and energy-efficient mixing performance, particularly in high-solids conditions (6% TS), as compared to linear motion and pump mix alternatives. Platforms installed provide access to Anaergia service boxes (Fig. 3), which enable in-situ mixer access without interrupting AD operations. Each mixer is mounted to a vertical post inside the digester allowing for height and attack angle adjustments to achieve optimal mixing, resuspend settled grit, and break scum accumulation in upper layers. The SST and accessory equipment were installed adjacent to Dig. 1, reducing pump energy, footprint, and impact on WQCP operations. Dig. 1 was brought online on January 5, 2021. Recuperative thickening was initiated in February and achieved steady performance in April (Fig. 4). Third-party performance testing was conducted in conjunction with Anaergia from April to July 2021. The below performance criteria were evaluated and achieved (Table 5): -Min. volatile solids reduction (VSR) above 57% for 80% of the time over 90-day test period, over a 30-day moving average (Fig. 5) -Demonstrate stable digester operation with volatile fatty acid (VFA)/alkalinity ratio <0.2 (Fig. 6) Testing further confirmed successful HSD in Dig. 1 as demonstrated by increased digester feed volumes, TS loading, and VSR. A third-party Lithium-ion Tracer test was conducted to confirm achievement of mixer performance requirements. The independent study (1) validated achievement of Anaergia's high-performance mixing standard (>90% of digester volume >0.3 ft/s) and (2) aligned with CFD modeling of mixer performance, which indicated superior performance compared to alternate mixing technologies. Co-Digestion Pilot: In July 2022, following successful completion of performance testing, the WQCP began a pilot program to receive 1-2 deliveries per day of slurried food waste. The organic slurry is produced at the South Bayside Waste Management Authority's Shoreway Environmental Center. The materials recovery facility (MRF) employs an Anaergia Organics Extrusion (OREX) press and Organics Polishing System (OPS) to remove contamination from commercial source separated organics and create a clean, homogenized, pumpable organic slurry. The slurry is pumped into 5,000-gallon liquid tanker trucks and hauled approximately 15 miles from the MRF to the WQCP. The slurry is fed to Dig. 1 for co-digestion with indigenous biosolids. The high-solids digestion upgrades have facilitated the pilot by provided excess capacity for external feedstock, as well as high-solids mixing capability within the digester to maintain digester health and mixing performance. WQCP monitoring indicates significant increases in biogas production since the initiation of high-solids digestion and co-digestion, respectively. Ongoing data collection during the pilot will inform planning and design of food waste receiving and biogas utilization upgrades to facilitate long-term co-digestion and advance energy-neutrality at the WQCP. Note that the high-solids digestion design was developed to meet performance requirements and operational objectives requested by WQCP representatives and does not maximize use of Dig. 1 volume. Operation at higher solids would further increase digester capacity for future growth needs or expanded co-digestion. Conclusion: The Omnivore system effectively addressed the biosolids and residuals management needs of the WQCP leveraging existing infrastructure; provided third-party validated performance improvements; and facilitated a successful food waste co-digestion pilot. As a result of the project's success, the below benefits were delivered to the WQCP: -Avoided major capital expenditure of an additional digester -Addressed capital improvement needs -Redundant digester capacity -Reliable production of stabilized biosolids -Improved digester performance -Improved mixing performance -High-efficiency mixers with lowest overall lifecycle cost -Future-proofing for load growth and changes in feedstock composition -Enable co-digestion of organic waste -Increased biogas production and energy neutrality The cost-effective retrofit has the ability to unlock additional digester capacity and increase redundancy while simultaneously improving digester performance. With the additional AD capacity created, WRRFs can rapidly accommodate increased internal sludge loads, high strength waste (HSW) for co-digestion, and improve plant resiliency. A similar solution may be replicated at WRRF throughout North America to cost-effectively improve biosolids management while significantly enhancing the ability of municipalities to leverage existing infrastructure for meaningful resource recovery and energy neutrality.

Introduction Affinity Laws for pumps and fans are commonly known but why aren't they commonly known for decanter centrifuges? Dewatering performance has a large impact on overall wastewater treatment operations and understanding how modern decanter centrifuge technology has evolved is critical to selecting the correctly sized equipment. The optimized selection of a decanter centrifuge and its performance plays an important role in the cost of returned solids (solids recovery) and the cost of disposal (dryness of solids). The scaling methodology (Affinity Laws for Decanter Centrifuges) of capacity and performance becomes a crucial activity. The inner diameter of the bowl has historically been one of the main criteria for comparing decanter centrifuges. However, this approach has not been sufficiently accurate for the prediction of capacity or performance. The holding volume, geometry, and operating speeds all need to be compared. For this purpose, GEA has developed and validated a theoretical model by performing side-by-side field trials. The validation of the G x Volume affinity law (See Figure 1) demonstrates that G force combined with volume are reliable criteria for the scaling of capacity and performance of decanter centrifuges for dewatering in wastewater treatment plants. Hypotheses 1. Comparing geometrically similar decanter centrifuges with an equivalent volume with a higher G force would result in either a higher cake dryness or a greater capacity. See figure 2 2. Comparing decanters with a different bowl diameter but with the same G volume, the performance and capacity would be the same. See figure 3 Methodology 1. Side-by-side operation with two equivalent bowl diameter decanter centrifuges with different G-volume was performed at WWTP Langenberg, Germany, keeping other parameters such as sludge characteristics, concentration of infeed sludge and solids recovery identical. 2. Side-by-side operation with two different bowl diameter decanter centrifuges with an equivalent G volume was performed at WWTP Oldenburg, Germany, keeping other parameters like sludge characteristics, concentration of infeed sludge and solids recovery identical. 3. In both trials, the services of KBKopp (Dr. Julia Kopp) were utilized to determine the maximum sludge dewaterability. See figure 4 for photos of the test equipment and site Results The research establishes that centrifuges with an equivalent bowl geometry, but having different G volume owing to rotational speeds, will have an equivalent capacity at the same performance level or a different performance at the same capacity. The capacity and performance is directly proportional to the G volume difference, and only indirectly related to the bowl diameter. See figures 5, 6, 7 Implications The study brings forward 'G x Volume' as reliable criteria for scaling and selection of decanter centrifuges in wastewater treatment plant design and also brings a paradigm shift from conventional wisdom of bowl diameter as the comparative driver. The research helps in selection of centrifuges that get higher capacity per square meter space or significant reduction in cost of operation (disposal and polymer consumption) per cubic meter of sludge handled. In either of the cases, 'G x Volume' based selection drives towards optimized scaling for reduction in CO2 footprint and an efficient circular economy. The Future The development and use of Affinity Laws for Decanter Centrifuges is on-going and is expected to result in more economically efficient and environmentally friendly operations.

1. INTRODUCTION Considering continuous generation of wastewater sludge in vast amounts and beneficial constituents, many countries have been using sludge on land. Nevertheless, land application of insufficiently treated sludge raises concerns due to transferring pathogens and trace pollutants, including toxic organics and microplastics (MPs) into the environment. MPs constitute a large portion of pollutants in sludge because of inseparable and versatile use of plastics in our daily life. Due to their small sizes (<5 mm), MPs can easily transport across environmental compartments and reach WWTPs in great amounts. WWTPs with modern technologies can remove MPs from wastewater with >90% efficiency but concentrate them in sludge. Anaerobic digestion of sludge is a widely used management option that stabilizes the sludge and reduces the amount to be disposed of. Various pretreatment methods have been developed to improve the efficiency of digestion such as thermal hydrolysis process (THP), chemical, and mechanical techniques. Recent studies have revealed that MPs can affect the efficiency of anaerobic digestion process.1 Furthermore, corresponding deteriorative effects of stabilization on MPs have been superficially addressed.2 Despite their stiff nature, exposure to abiotic factors such as heat, light, water, chemicals, and mechanical impacts may initiate structural changes and induce biodeterioration. For example, polyethylene terephthalate (PET), can hydrolyze to a certain degree in the presence of alkaline solutions due to saponification process in ester linkages. In addition, they can hydrolyze in wet conditions at high temperatures as in the case of THP.3 For the first time in literature, this study investigates whether alkaline pretreatment, THP and combined alkaline and thermal hydrolysis pretreatment (ATHP) processes applied for sludge disintegration and biogas enhancement can concurrently deteriorate PET MPs and lead them biodegrade during anaerobic digestion. Moreover, the study investigates the effects of different concentrations of MPs on digestion efficiency. 2.MATERIALS AND METHODS WAS and anaerobically digested sludge (ADS) were taken from a conventional WWTP serving a population of 4 million with a capacity of 765,000 m3/day. The model PET MPs were obtained by cutting water bottles into square shapes using scissors. Then, the particles were passed through a series of sieves to obtain MPs in sizes of 250-500 µm. WAS solubilization efficiency of three different disintegration techniques (i.e., alkaline, THP, and ATHP) were tested in varying conditions by monitoring soluble COD (sCOD) of WAS, which was spiked with 3 mg PET/g TS. Alkaline pretreatment was carried out for 5 days by dosing WAS with 0.5 M alkali using KOH and NaOH at 0.10 and 0.40 M, respectively. THP was performed at 127 °C and 1.7 bar for 30, 60 and 120 min using an autoclave. In ATHP, WAS samples (three sets) which had been alkaline pretreated (0.5 M) for 2, 4 and 5 days were autoclaved at 127 °C for 120 min. PET MPs collected from pretreated WAS were analyzed using SEM and FTIR to observe the changes they experienced during pretreatment. Biochemical methane potential (BMP) reactors of pretreated and unpretreated sludges spiked with 0, 1, 3, 6 mg PET MPs/g TS were set up in triplicates at a food-to-microorganism ratio of 1, and a total solids content of 2%. Reactors were coded as R0, R1, R3 and R6, with the letter P added for disintegrated reactors. All reactors were operated for 60 days under mesophilic conditions. Reactors were monitored for gas production throughout their operation. At reactor termination, digester performance and plastic characteristics were analyzed. 3.RESULTS AND DISCUSSION As shown in Table 1, disintegration degree (DDCOD) reached up to 81% by alkaline pretreatment in 5 days. Considering the most evident increase (71%), two days alkali pretreatment was selected. As the duration of separate THP was prolonged, solubilization increased only slightly and reached to a DDCOD of 19% at a maximum, comparable to literature.4 Although there was no notable difference beyond 30 min, 120 min was selected as the main purpose was exposing MPs to stress conditions before anaerobic digestion. Figure 1 shows that solubilization achieved in two days of alkaline pretreatment was improved with the addition of THP. However, the contribution of THP became relatively small beyond two days of alkaline application. Two days of alkaline application and a subsequent 120 min THP was selected for ATHP, which altogether resulted in DDCOD of 79%. MPs extracted from pretreated sludges were analyzed for changes in physical and chemical structure by evaluating their FTIR spectra and SEM micro-photographs comparatively with control samples. PET exposed to different pretreatment processes experienced varying levels of changes in different regions of the polymer structure, which differentiates the impacts of thermal and chemical stress factors. Both alkaline pretreatment and THP caused an overall decrease in the absorption intensity of PET. Crystallinity of the polymer increased the most with THP and followed by ATHP. Alkali treatment did not cause a significant change. Therefore, heat application might be the mechanism of increasing the crystallinity of ATHP pretreated PET. This is possibly due to the formation of new crystalline zones in polymer's structure from the breakdown of branches in backbone and bending on themselves. Partial melting and the recrystallization of the amorphous region of the polymer can be the reason of increase in crystallinity. It is evident from Figure 3(a) that MPs exposed to alkaline environment experience a strong surface peeling in comparison to untreated samples. Furthermore, THP seems to cause the corners of the square-shaped MPs to expand outward compared to those of untreated MPs. When two techniques were combined, the notable peeling effect caused by alkaline pretreatment diminished to a great extent, possibly due to the heat applied afterwards. The expanded MPs lost the previous changes occurred on their surfaces and reformed, but the cross-sectional layers appeared. As shown in Figure 2, ATHP pretreated reactors produced statistically higher amounts (22.0%) of methane than unpretreated ones regardless of the MPs dose. This can be attributed to that pretreatment process overwhelmed the impact of MPs on digesters. In contrast, the dose of MPs significantly affected the methane yield of unpretreated reactors. Among unpretreated reactor sets, R3 yielded the highest methane production (p<0.05), which was followed by R6, R1 and R0, in decreasing order. Both crystallinity and carbonyl index of MPs showed smaller changes by anaerobic digestion compared to more dramatic effect of sole ATHP. Figure 3(b) shows that there was an observable predominant impact of digestion, giving the MPs a squashed surface appearance and decreased surface thickness at some points. These images supported the current claim that MPs pretreated prior to anaerobic digestion becomes more prone to microbial attack. Acknowledgement: This study was funded by TUBITAK through the project grant 121Y156.

Introduction The waste activated sludge (WAS) produced in Washington Suburban Sanitary Commission's (WSSC Water) Water Resource Recovery Facilities (WRRFs) is historically known to have relatively poor digestibility, even with thermal hydrolysis pretreatment (THP). In agricultural waste management, it has been a common practice to co-digest a poorly biodegradable feedstock with an easily biodegradable feedstock to improve the overall digestibility of the former (Karki et al., 2021). Since primary sludge (PS) generated in WRRFs usually possesses much better digestibility over that of the WAS, this study tested the hypothesis whether blending PS with WAS can increase the biodegradability of WAS. Because WRRFs need to use more coagulants such as alum to precipitate more PS for the blending, the impact of alum on the WAS biodegradability was also taken into consideration. Therefore, this study investigated the effects of PS:WAS blending ratio and alum doses on the WAS digestibility in a THP-anaerobic digestion system. Meanwhile, this study also tested the hypothesis that blending PS with WAS may produce more recalcitrant dissolved organic nitrogen (rDON) as a result of Maillard reaction in THP (Zhang et al., 2020). Maillard reaction occurs between the carbonyl groups of reducing sugar and the amino groups of proteins (Hodge, 1953). Since PS and WAS are mainly composed of carbohydrates and proteins, respectively, and the typical THP temperature at 165 0C is ideal for Maillard reaction, it is a reasonable prediction that more rDON may form within THP fed with PS and WAS blending than without. Materials and Methods Experimental design Dewatered WAS and PS cake samples with around 20% total solids (TS) were collected from two WRRFs of WSSC Water. Depending on the Al that came with each type of cakes, additional Al was supplemented according to the Al doses designed in Table 1. Basically, more Al was supplemented when more PS was blended to simulate the scenario when more alum was consumed for more PS production. A jar test was performed to estimate the Al dose it took to produce enough PS for the blending ratio in Table 1. Then, the PS and WAS cake samples were either individually processed in THP-anaerobic digester (AD) systems as controls or blended according to the blending ratio as summarized in Table 1 to study the blending effects during this three-phase study. All cake feedstocks were diluted to 16% TS prior to feeding into the CAMBI pilot THP system operated at 165 oC for 30 min. The THP effluent was further diluted to 9% prior to being fed into the four pilot mesophilic AD systems. These ADs were inoculated with fresh effluent sludge from a full-scale THP-fed mesophilic AD at DC Water. The steady-state digestates were analyzed for understanding the impacts of PS:WAS blending ratio and alum doses on WAS digestibility. In general, four phases of studies described in Table 1 were performed with controls to understand the effects of 1:1 blended with low Al in phase I, 1:1 Blended with high Al in phase II, and 3:1 Blended with high Al in phase III. rDON determination The four AD effluent samples from Phase II study in Table 1 were subjected to a rDON test. This test was divided into two steps including air stripping and aerobic incubation. The goal of air stripping was to reduce the total ammonia nitrogen (TAN) of the AD effluent to lower than 200 mg/L. This is because the TAN concentration is significantly greater than that of dissolved organic nitrogen (DON) and thus may overshadow the DON level readings which are calculated as the difference between soluble Kjeldahl nitrogen and TAN. The aerobic incubation aimed to remove the biodegradable DON, and in turn the remaining DON in the system can be regarded as rDON. Results WAS digestibility The volatile solid reduction (VSR) has been used as an indicator of sludge digestibility (Luo et al., 2022). Hence, the steady-state VSR of all digesters were determined. Assuming the VSR of PS does not change with and without blending, the blended WAS VSR can be calculated and compared to the control WAS VSR without blending and Al supplementation to assess whether the WAS digestibility has been improved. As can be seen from Figure 1, the WAS VSR did not change with and without blending with PS at a 1:1 ratio without external Al addition. This means blending PS at this low ratio does not improve the WAS digestibility. When a low dose of Al was added to increase the blended sludge background Al level from 1.49 to 1.95%, it can be seen that WAS VSR decreased about 2%, indicating the inhibitory effect of Al on WAS digestion. The reduced hydrolysis rate as a result of binding between Al and protein in WAS has been regarded as the reason accounting for the WAS digestibility decrease (Luo et al., 2022). This conclusion was reinforced by the fact that WAS VSR substantially decreased to 15% when further increasing the background Al level from 1.95 to 2.85% without changing the blending ratio (Figure 1). It is interesting to see that tripling the PS blending ratios can bring WAS VSR back to 28% even when the same high Al dose (2.85%) was used in the sludge mixture. These observations suggest that co-digesting PS with WAS does not directly improve WAS digestibility; however, adding more PS does mitigate the Al inhibition on WAS digestion. It was reported in a previous study that Al is expected to play greater binding effects on WAS than on PS because the affinity of Al to proteins in WAS is higher than that to the polysaccharides in PS (Luo et al., 2022). Therefore, PS might be able to prevent the binding between Al and protein in WAS by acting as a barrier. Hence, the reduced binding potential between Al and protein in WAS could mitigate the Al inhibition on WAS digestion. rDON The centrates containing DON generated from all four digesters in phase II study (Table 1) were exposed to aerobic incubation for 14 days. Profiles in Figure 2a showed that centrates from PS only and blended sludge with high Al addition contained the least DON. PS does not contain much protein and thus is reasonable to produce less DON. Al ¬ is known to be capable of precipitating DON (Zhang et al., 2020), which may explain the low DON level in centrate with high Al addition. In contrast, the DON levels in both WAS only and blending sludge without external Al addition were two times greater. The same trends were also observed with the residual DON, namely rDON in Figure 2b. It should be pointed out that the rDON level in blended sludge was actually substantially greater than the average level from the two individual sludge without blending, indicating extensive Maillard reaction might have occurred when PS and WAS were blended. Conclusions It can be concluded from this study that blending PS does not directly improve the WAS digestibility. Instead, blending more PS did mitigate the inhibitory effect of Al on WAS digestion. However, blending PS with WAS promoted rDON formation due to Maillard reaction between the two types of sludges.

Introduction The Woodman Point (WP) Water Resource Recovery Facility (WRRF) is owned and operated by Water Corporation. The WP WRRF is the largest treatment plant in Western Australia and services industrial, commercial, and residential customers in the southern Perth metropolitan region. The WRRF liquid stream treatment process was upgraded in 2019 to provide 180 ML/d wastewater treatment capacity (approximately 900,000 equivalent population). The Water Corporation selected a 120 tDS/d design horizon for the next WP solids handling upgrade, which corresponds roughly to the 180 ML/d design horizon and includes dewatered solids imported from regional WRRFs. Growth in the WP WRRF catchment is projected to continue beyond 250 ML/d and 160 tDS/d (including imported solids) in 2060. The existing egg-shaped digesters (ESDs) at WP WRRF use mesophilic anaerobic digestion to stabilize combined thickened primary sludge (PS) and excess activated sludge (EAS) into digested sludge (EAS is equivalent to Waste Activated Sludge), which is then dewatered into biosolids cake, suitable for direct beneficial use in agriculture under the Western Australia (WA) Guidelines for Biosolids Management. Biosolids must be Pathogen Grade 3 (P3) (equivalent to Class B), Contaminant Grade 2 (C2) or of better quality to be suitable for direct beneficial use in agricultural land. Without an upgrade to the current solids handling process, achieving the P3 C2 requirement is at risk. The only alternative for management of off-specification biosolids is landfill disposal, which is financially and environmentally unsustainable. Water Corporation completed a planning study in 2019 that identified EAS only thermal hydrolysis process (THP) and EAS only carbonization process as preferred technologies for consideration. The principal driver for implementing THP is achieving a design minimum digester solids retention time of 15 days within the existing digesters to meet P3 requirements. Carbonization was identified as an technology to potentially augment digestion capacity and manage emerging contaminants of concern, notably Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) and microplastics. Methodology Six different process options utilizing one or both of Water Corporation's preferred technologies, THP and carbonization, were evaluated to select the preferred process configuration for the WP solids handling upgrade. These options included: -EAS only THP PS and hydrolysed EAS are digested in the existing ESDs. -EAS only carbonisation PS is digested in the existing ESDs and undigested EAS to diverted to a new carbonisation facility. -Full THP Hydrolysed PS and EAS are digested in the existing ESDs. -Full THP with digestate carbonisation Hydrolysed PS and EAS are digested in the existing ESDs, and digestate is diverted to a new carbonisation facility. -Intermediate THP (i-THP) PS is digested in a new ESD. Digested PS and EAS are hydrolysed and digested in the existing ESDs. -Post THP PS and EAS are digested in the ESDs, with additional ESD capacity provided. Digestate is hydrolysed and dewatered. Dewatering centrate is returned to the digesters for further digestion. Simplified block diagrams for each option are presented in Figure 1 through Figure 6. Mass and energy balances were completed, incorporating key inputs from vendor-specific equipment/processes. Key outputs from the mass and energy balances are presented in Table 1. Post digestion THP was not evaluated in detail as it required the greatest additional digestion capacity, despite potentially providing the highest dewatered cake solids concentration. Results The THP options were assessed to be the most favorable options based on a multi-criteria assessment. One of the key drawbacks considered for THP is that it cannot manage emerging contaminants (including, but not limited to, PFAS and microplastics). The current regulatory environment does not require management of these contaminants. As a result, carbonization was considered as a future augmentation if PFAS were to become strictly regulated. The key drawbacks of biosolids carbonization at the time of evaluation was the technology was considered to be embryonic and not sufficiently established at full scale to be implemented with confidence by 2024 without any onsite trials, and there is uncertainty in acceptable the biochar bi-product end-uses in Western Australia. EAS only THP was selected as the preferred option as it balances initial capital expenditure by intensifying the existing process capacity, enhances generation of biogas, and allows for future implementation of other process options (including energy neutral carbonization). EAS only THP also provides the greatest (net positive) energy balance, without requiring supplemental fuel for heat/steam during normal operations. The EAS only THP option provides the flexibility to increase future plant capacity with another THP train and/or construction of the fourth ESD and implementation of i-THP. The capacity can be augmented in stages to manage capital investments. Alternatively, digestate carbonization can be implemented at any stage, with the benefit of having fully or partially digested solids as the feed to the thermal dryer, reducing the drying capacity required. Carbonization can also be implemented to manage emerging pollutants or minimize transport of the end product off-site. Figure 7 show the concept design layout of the EAS only THP implementation, with areas for future expansion. Conclusion This paper will benefit the water utilities, and consultants as it demonstrated how both THP and carbonization technologies can be complementary. EAS only THP was determined to be the preferred option for the 120 tDS/d solids upgrade, and a staged implementation approach to carbonization was identified for consideration beyond the 120 tDS/d. EAS only THP maintains the current biosolids quality required for the projected growth in plant capacity and balances initial capital expenditure by intensifying the existing process capacity while allowing for future implementation of other process options such as carbonization if PFAS were to become strictly regulated.

This paper and presentation will survey and analyze the latest lawsuits and regulatory developments affecting the beneficial use of biosolids, including compost, to provide wastewater and residuals professionals current information that will help inform their decisions on risk, liability, management, and planning. Slaughter and Silton regularly defend land application in litigation, and counsel both POTWs and biosolids service providers on regulatory issues. The speakers will discuss the challenges posed by local ordinances, tort litigation, and the ongoing campaign to regulate per- and polyfluoroalkyl substances (PFAS) in biosolids and groundwater. This talk will outline potential risks, while also highlighting strategies for managing land application and discouraging attacks on beneficial use in the face of a changing legal environment and local communities that may be hostile to land application. Slaughter and Silton will first address the dynamic and problematic regulatory landscape for land application, highlighted by Maine's ban on land application because of trace PFAS. Federal, state and local legislators and regulators, at the behest of many advocacy groups, have turned their focus to PFAS and other trace chemicals that may be found in biosolids. These efforts have spurred regulators to take a variety of actions, including EPA's September 2022 proposal to designate two PFAS-PFOA and PFOS-as hazardous substances under the federal Superfund statute. If the proposal is adopted as a final rule, it could pose risks to land appliers and POTWs. Silton and Slaughter will survey recently regulatory developments and their implications for POTWs, biosolids service providers, and farmers, including ongoing litigation challenging some of the stringent PFAS regulations. Slaughter and Silton will also address the interplay between state and local regulation by exploring several case studies involving local attempts to restrict or ban land application. Their discussion will cover California, where decade-long litigation over a local biosolids ban resulted in a trial and settlement striking down the ban. City of Los Angeles v. Kern County, 2017 WL 1292822 (Tulare Co. Super. Ct. Mar. 14, 2017). Notably, the Kern trial resulted in findings that land application poses few risks after hearing evidence concerning minimal concentrations of PFAS in soil and groundwater beneath a farm where biosolids had been land applied for decades. The speakers will also address recent developments in other states, including Pennsylvania, where the speakers recently challenged enforcement of a local waste ordinance against land application. Second, the speakers will survey risks to land application posed by tort lawsuits. The risk of tort lawsuits based on trace PFAS in biosolids, soil, and groundwater will be examined. Cases in which plaintiffs' lawyers have alleged nuisance conditions caused by land application will be discussed, including the important decision of the Pennsylvania Supreme Court in Gilbert v. Synagro Central, LLC, 131 A.3d 1, which ruled that farming with biosolids is a normal agricultural operation entitled to protection under Pennsylvania's Right to Farm Act. The presentation will conclude with how stakeholders in land application-POTWs, contractors, and farmers-can collaborate to reduce their risks and navigate a challenging, dynamic legal and regulatory landscape.

Introduction: Odor complaints often originate from neighbors near odorous sources, such as industrial facilities. Typically, when a complaint is filed with a regulatory agency, the agency sends an inspector to the location of the complaint to verify the odor. Data recorded from this method is often sporadic and can be unreliable, as many inspectors do not arrive at the site for hours or even days, long after the odor has vanished. This paper presents the conceptual framework for a community-based odor app ('Community OdorApp') that provides a mechanism for members of the public to report odors directly through a web-based program. The Community OdorApp overcomes many of the limitations of current odor complaint and response approaches and offers a cost-effective strategy for facilities, municipalities, and/or other odorous sources to engage with their communities. Background In 2013, Ramboll US Consulting, Inc. introduced a facility-based odor app ('Facility OdorApp'), which is a data acquisition and management system that allows facilities to track their own odor patrol efforts. The Community OdorApp aims to build on the Facility OdorApp, overcoming some of the limitations of the Facility OdorApp by integrating public participation (i.e., crowdsourcing). Crowdsourcing is growing in popularity and utility. Currently, there are numerous apps that leverage crowdsourcing to provide a public benefit (e.g., Waze, MiFlight, Street Bump). The Community OdorApp provides a public benefit not only by making it more convenient to report odors, but also by providing the community with information about odor 'hotspots' and allowing the community to participate in understanding and potentially addressing odor problems. While there are some existing applications, deployed or under development, that are designed to record odors reported by the community (e.g., Smell PGH, Smell MyCity, EPA's Odor Explore), these applications have limitations, such as lacking weather data to trace the source(s) of the odors and not providing a variety of useful analytical tools to analyze odor trends. As discussed below, the Community OdorApp has features that advance the state of the science, allowing users of the app to analyze and act upon the data collected. Design The Community OdorApp, which operates on any web-enabled device (e.g., computer, tablet, smartphone), collects data from the public via a browser-based form that has a simplified, user-friendly interface. The app requires that the user share their location to verify the authenticity of the report but does not require the user to enter any other identifying information. The user can then input the date and time of the odor occurrence, which allows the app to retrieve contemporaneous weather data from nearby weather stations. The next screen on the app requests odor-specific information, including the offensiveness of the odor and a description of the odor. Next, the app requests information about odor duration. Finally, there is a comment section for additional information, and then the report can be submitted. Once a report is submitted, it is immediately incorporated into the app's backend database, which offers various reporting features and analytical tools, including raw data download, site map, heat map, and several data analysis charts (see examples in Figure 1). With this information, interested parties can quickly analyze the data, identify potential odor sources/trends, and take action to address odor issues. Discussion The Community OdorApp offers numerous advantages over traditional odor complaint and investigation approaches, including: -Faster response to odor complaints since the data gets reported directly to the sponsoring entity who can respond immediately rather than having to wait for a regulatory agency to send an inspector to the site. -The app saves time for the complainant since complaints can be logged directly over the internet rather than having to call the local regulatory agency. -The app allows odors to be reported from a broader geographic area, as it does not rely on odor surveillance restricted to fixed routes which is often the case with facility-based odor patrol. -The app typically provides more complete information on odor start/end times and duration because the complainant often lives or works at the location of the odor and therefore has knowledge of the history of the odor, unlike an inspector who may only visit the location for a brief period. -The data for the app is free since it is provided by the public, rather than having to pay an employee or third party to collect the data as is frequently done with facility-based odor patrol. -The app can be used to educate and inform the public by summarizing key findings via periodic reports, which can be posted on the app's landing page. Despite these advantages, the Community OdorApp also has some limitations/challenges, such as: -Since the Community OdorApp collects data via a public-facing website, abusers of the app could enter erroneous or false data. However, the Community OdorApp has features that are designed to protect against this. Specifically, the app documents the location of each user via GPS or IP address, so it is possible to ascertain if complaints are coming from a single or appropriate location. - Since the Community OdorApp collects location information on each user, this raises potential data privacy concerns. To help protect data privacy, the app uses a differential privacy strategy, where the location of each complaint is shifted slightly to still locate the odor event without revealing the exact location of the user. In addition, the app is built on the Google App Engine, which has multiple layers of security to protect data once it has been submitted. -The quality of data submitted to the Community OdorApp could be questionable since the users are not typically trained odor inspectors. However, the app helps to maintain data quality by presenting the user with a simple form with mostly pre-determined, forced-choice options (e.g., drop down menu, radio button). This data collection approach also helps to ensure that data is recorded in a consistent fashion to facilitate data analysis and reporting. -The Community OdorApp works best when it has many users; however, promoting the availability of the app can be a challenge. The entity sponsoring the app will likely need to utilize multiple communication channels (e.g., email distribution lists, phone calls, text messages, video, radio, social media, etc.) in order to attract users. Implications The Community OdorApp has the potential to shift the paradigm of odor complaints from one in which neighbors are working against an odorous source to one in which neighbors are working together with the odorous source to provide useful data that can help identify and solve odor problems. In this regard, the Community OdorApp has the potential to strengthen the relationship between odorous sources and their neighbors, thereby allowing critical public service facilities such as wastewater treatment facilities and landfills to continue operating in the communities they serve. The app helps everyone gain a better understanding of odor patterns affecting local communities and provides data to create solutions. With the success of this app, it could lead to the development of many more crowdsourcing apps with environmental applications (e.g., noise pollution, air quality, wind, water quality, wildfires, natural disasters, etc.).

The call to meet industry standards and operate according to best practices is one which all industry professionals can appreciate, but where standards are clearly outlined best practices is far less concrete. Within the residuals and biosolids treatment industry, that which constitutes best practices can vary greatly across facilities depending on a number of factors. In the spirit of diminishing this ambiguity, three case studies examining industrial dewatering and thickening systems at separate facilities will be presented. Two of the featured case studies will focus on dewatering; the first facility produces primarily inorganic residuals while the second facility's dewatering process treats starch-laden residuals. The third study also focuses on organic residuals and biosolids treatment, however their overall treatment involves a thickening process for relatively unique biosolids disposal which could be mutually beneficial for manufacturers and municipal processors alike. This presentation will include analysis of the technical aspects in each case study and a discussion of related findings. STUDY 1 DEWATERING INORGANIC RESIDUALS The subject of the first study is a facility which manufactures paint and coatings for electronic devices. In many treatment systems, flocculation is a vital step in dewatering solids. While this facility integrates flocculants, the waste stream composition poses additional challenges. Treatment begins in reactor tanks with coagulants, flocculants, and precipitants before being transferred to a clarifier. However, because this facility's residuals are predominantly inorganic, these residuals cannot effectively form the floc structure which renders a more manageable sludge suitable for common technologies like the belt filter presses or screw presses. Because popular technologies are ill-equipped to process this facility's distinctly tacky sludge, operators rely on a plate and frame filter press for dewatering (see Figure 1). Plate and frame filter presses are comparatively inexpensive, but despite cost-efficiency this press is subject to drawbacks which would typically disqualify its utilization in other facilities. These drawbacks, including reduced processing capacity and specific labor demands, are non-issues for this facility as operation occurs at a smaller scale. Because this sludge has a challenging consistency, the plate and frame filter press allows this plant to meet municipal limitations for proper disposal. Data obtained onsite reflected 2.0% feed solids was easily able to be dewatered to 28% cake solids, with a capture rate of 96%. STUDY 2 DEWATERING ORGANIC RESIDUALS The second study highlights a food processing facility which prepares potato chips. This facility's waste stream is marked by its high concentration of starch and starchy residuals. Due to the starch and water binding at an infinitesimal level, pressing alone cannot sufficiently dewater residuals. Therefore, this facility has incorporated a technology that may not adhere to wider perceptions of best practices. After its initial biological treatment in aeration basins, the waste solids are directed to a volute press. Onsite sampling reflected 2.1% feed solids was able to be dewatered to 17% cake solids but with a capture rate of only 79%. Figure 2 shows the cake from the volute press of this process. While volute presses may not meet high capture rates (see Figure 3), the resulting sludge does meet minimum requirements for municipal disposal. This choice could be seen as a failure to meet industry standards or best practices; however, this case study offers a fair example of a facility achieving balance between efficient operation and regulatory compliance. STUDY 3 THICKENING ORGANIC RESIDUALS The final case study features a second food processing plant. This plant, which produces a variety of sauces and condiments, has a waste stream with a high concentration of fats, oils and greases (FOGs). Processing FOGs can create undue strain on equipment, leading to wear and potentially shortening its operational lifespan. In this case, a complex system of treatment and retreatment is employed to maximize separation. The waste stream processing begins with an oil and water separator. After undergoing a biological process to remove contaminants, the waste stream moves to two dissolved air flotation devices (DAFs) which take 0.98% feed solids and thickens it to a 9.10% thickened solids product. Skimmed floatate, a gel-textured product shown in Figure 4, is transferred to a hopper. But what occurs next makes this study particularly noteworthy. Rather than disposing the end-process gel, this facility stores it in a silo onsite. Daily, the material is transported offsite to a nearby farm where the gel is applied as crop fertilizer. This stands out as an instance beneficial reuse, which is rare for industrial biosolids. This practice results in lower disposal costs for the facility. This beneficial reuse simultaneously benefits the municipal processers because the receiving POTW need not process FOG-laden wastewater or fine the facility for exceeding allowable effluent pre-treatment parameters. At a time when manufacturers in all areas are finding new and creative ways to meet corporate and social demands for sustainability, this type of process is an exemplar. However, as the previous case studies demonstrated this may not be in other manufacturer's' operational capacity or best interests. CONCLUSION Ultimately, the combination of unique waste streams, facility production capacity and local disposal options function in concert to outline best practices on an individual basis. The value of efficient operations cannot be overstated, but to truly thrive facility operators must be able to achieve maximum efficiency while also complying with oft-changing regulations. Failure to achieve this balance risks company resources and a cooperative relationship with municipal waste processors. By examining and comparing facilities' pre-existing treatment systems to post-upgrade systems against prevalent norms in the wider treatment landscape, we gain greater insight regarding the fluidity of best industry practices. This comparison will also yield a greater technical understanding for industry professionals as we compare capture rates and efficacy of various techniques across diverse waste streams' compositions. Finally, in addition to generating insights through analysis, this presentation will highlight how residuals and biosolids treatment systems impact municipal treatment facilities and vice versa. This discussion is intended to help reposition municipalities as a cooperative partner with a vested interest in the treatment process and industry.

INTRODUCTION Anaerobic digestion is often used in larger wastewater treatment plants (WWTPs) in order to generate energy rather than consuming it. However, operating only in a reducing environment limits biodiversity and can create undesirable consequences. As such, research has started taking a harder look into the benefits of post-aerobic digestion (PAD) following anaerobic digestion. Having a long history of researching and improving aerobic digestion methods, Thermal Process Systems (TPS) sought to apply its existing technologies and knowledge of aerobic digestion to a two-stage anaerobic digestion system. One of the common issues faced by anaerobic digesters is becoming volatile fatty acid (VFA) overloaded. This occurs as a result of the acidogens making VFAs faster than the methanogens can convert the VFAs to methane, limiting the energy produced by the process. Two-stage anaerobic digestion was used to separate out the more rapid stages of hydrolysis and VFA formation from the much slower step of methane production in order to improve the conversion of organic material to usable energy. Optimizing and stabilizing the anaerobic digesters significantly reduces the oxygen demand in a post-aerobic digester, increasing the energy output while reducing the energy requirements. The primary goal of coupling aerobic digestion to anaerobic digestion with a recycle stream was to improve the stability of the anaerobic digester and resulting product by increasing the volatile solids reduction (VSR), improving biogas production and quality, reducing the overall hydraulic retention time (HRT) for the digestion process, and improving the dewatering characteristics. This was primarily achieved by establishing process control parameters around the pH of the anaerobic digester by varying the recycle rates. METHODOLOGY Operation of the pilot unit commenced without utilizing a recycle from the aerobic digester to establish a baseline of operations. During the initial phase of the pilot demonstration, the operational liquid levels of each tank was set so the fermentation tank, methanogen reactor, and aerobic digester operated at 2-, 15-, and 8-day hydraulic retention times (HRTs), respectively. Each phase of the pilot demonstration lasted for three sludge ages of steady-state operation. After the first phase of operating in a plug-flow fashion, the recycle was initiated at 60% of the daily feed amount. The recycle rate was later increased to 80%, 100%, and 150% of the daily feed amount to observe the ability of the system to reduce the struvite precipitation potential in the anaerobic digester by decreasing the ammonia and pH. Continuous monitoring of the system was carried out with the use of Endress & Hauser temperature/ORP/pH probes, liquid level pressure transducers, and vacuum/pressure gauges. The routine liquid analysis of each digesters' contents was carried out with the use of Hach colorimetric test kits. The routine biogas analysis was conducted with the use of Sensidyne gas detection tubes. Theoretical calculations of the potential for struvite formation were performed with the 'Struvite Tool' Microsoft Excel plug-in produced by the Office of Water Programs at CSU Sacramento. Dewatering results were obtained by sending samples to Centrysis Centrifuge Systems in Kenosha, Wisconsin. RESULTS The plug-slow operation of the pilot unit resulted in the methanogen reactor becoming VFA overloaded. This was accompanied by a decrease in the VSR, biogas production, and methane concentration in the biogas. Initiating the recycle rapidly lowered the VFA to alkalinity ratio (VFA/ALK) in the reactor; bringing it to literature values that designate a healthy anaerobic digester. The VFA/ALK was maintained at proper values without spikes in the VFA concentration or foaming events in the methanogen reactor for the remainder of the pilot demonstration. The methanogen reactor consistently achieved 55-60% VSR with the recycle in effect. Dewatering results from the centrifuge manufacturer showed a significant improvement to the dewatering characteristics of the digested biosolids, as the aerobic cultures used are capable of breaking down the extracellular polymeric substances often produced by anaerobic digestion. No coagulant and only 18 active pounds of polymer per dry ton of biosolids were required to achieve 32% TS in the dewatered cake. Not having a requirement for standard metal salt coagulants reduced the amount of phosphorus in the biosolids cake; bringing the nitrogen to phosphorus ratio in the cake to the range that agronomic studies suggest makes up a healthy soil. Increasing the recycle through the system effectively allowed the aerobic digester to remove a larger mass of ammonia from the methanogen reactor daily. The decreasing ammonia was accompanied by a controlled pH adjustment in the reactor. The methanogen reactor maintained less than 500 mg/L of ammonia and a pH of 6.8 throughout the steady-state portion of this phase of the pilot; levels that theoretically eliminate the production of struvite. The actual data obtained during the pilot demonstration showed the decreasing ammonia and pH subsequently led to an increase in the soluble ortho-phosphate present in the digester. These effects were not accompanied by a decrease in the VSR or biogas production. Another observed result that was observed was the H2S in the biogas became non-detectable with the 1 part per million gas detection tubes. The GC results confirmed this observation with a reported H2S concentration of 5.6 parts per billion while also confirming the methane concentration at 62% in the biogas. Further research discovered previously published discussions of the ability of nitrates to inhibit the activity of sulfate-reducing bacteria (SRB) that produce H2S by offering a more thermodynamically favorable electron receptor. The nitrates supplied by the recycle from the aerobic digester inhibited the SRBs while promoting a sulfur-oxidizing, nitrate-reducing bacteria (Lomas, 2005). This allowed the system to decouple the nitrification and denitrification processes by moving denitrification to the fermentation tank. DISCUSSION AND CONCLUSIONS This pilot demonstration showed the capabilities of coupling two-stage anaerobic digestion to a conditioning aerobic digester that recycled material through the system. The recycle supplied by the aerobic digester offset variations in the feed material, improving the stability and energy output of the anaerobic digestion process. Maintaining high VSR increases the total amount of methane produced through anaerobic digestion. High VSR combines with the reduction of dewatering chemical requirements and higher cake solids to offer substantial cost savings for facilities. The ability of the recycle to reduce the struvite potential in the methanogen reactor reduces maintenance concerns that often accompany anaerobic digestion. This is linked to the elimination of H2S in the biogas which removes the need for more expensive forms of H2S treatment and continuous maintenance of boilers and CHP units. The removal of H2S allows facilities to utilize the energy produced through anaerobic digestion on a more consistent basis. The capabilities of this system offer cost savings and solutions for problems that many anaerobic digestion facilities face.

Microplastics (MPs) are a kind of pollutants that have attracted widespread attention in recent years. Previous research shows that the vast majority of MPs will be intercepted by sludge after the wastewater enters the wastewater treatment plant (WWTP) 1), and will enter the soil with the subsequent utilization of sludge. Before the sludge enters the soil, it is usually subjected to a series of treatments such as high-temperature composting and methane fermentation. Methane fermentation is an energy conversion of sewage sludge, and its use will expand in the future. Recent study found that the shape, quantity and size of MPs in methane fermentation or high temperature composting of sewage sludge changed 2) but the reason and the MPs' characteristics was not deeply studied. This research study and summarized the characteristics of MPs in the sewage sludge before and after methane fermentation in Japan. We sampled sludge before and after methane fermentation at WWTP A and B in Japan several times in 2022 from June to December. Both WWTP A and B use methane fermentation for sludge treatment. WWTP A uses mesophilic fermentation while WWTP B uses thermophilic fermentation. After organic matter removal using H2O2, ultrasonic treatment, and density separation steps, the sludge sample will be screened for particles suspected to be MP using microscopy and their chemical composition will be determined using μ-FTIR (AIM-9000; Shimadzu.Corp.). This study is focus on non-fibrous MPs with particle size greater than 100 μm. The size (long axis and short axis) and the plastic type of every MPs were recorded, concentration by dry weight and monthly discharge of MPs were calculated. With the above information, the characteristics of MPs before and after methane fermentation of sludge were summarized. In the sludge samples in this research, the concentration of MPs ranged from 0.72×104 to 1.8×104 pcs per kg dry weight. (Figure 1.) Overall, WWTP A had a higher concentration of MPs than WWTP B. The sludge from both WWTPs showed 2.9%-37.1% of decrease in MPs' concentration after methane fermentation. The concentration of MPs in samples from the same WWTP did not show great fluctuations from month to month. If the change in the amount of MPs in the methane fermentation system is calculated from the input and production of sludge, the amount of MPs was reduced by 50.1%-71.1% after the methane fermentation. For the plastic type, PE was found in all of the samples, accounting for 9.1%-21.7%. The detection rates of PP, PP-PE, acrylic and ABS were higher than 75%, PVC, PMMA and EVA were higher than 50%. Some particles with the spectral characteristics of MPs but with an ambiguous spectral information, or with the spectral characteristics of several MPs at the same time were founded. These particles may have been subjected to degradation or may be a mixture of plastics. Although it was not possible to determine the exact type of plastic, these particles were determined to be MPs in this study. The maximum size of MPs observed in this study was 1637.5 µm. 86.5% of the MPs in the sludge were smaller than 500 µm, 8.8% of the MPs were between 500 and 1000 µm, and only 4.7% of the MPs were larger than 1000 µm. (Figure 2.) The particle size of MPs became smaller after methane fermentation in WWTP A. Before digestion, the range of 200-300 µm had the most MPs. After digestion, the range of 100-200 µm had the most MPs. In WWTP B, the range of 200-300 µm had the most MPs but after methane fermentation, the percentage of MPs in this range has decreased significantly. After methane fermentation, there was a decrease in MPs' quantity. The degradation of MPs may have occurred during methane fermentation. Since there is a lower limit of detection of MP size in the analytical and detection methods, the accuracy of analysis decreases near this lower limit, and effective analysis is not possible for MPs smaller than the lower limit of size, 3) the possibility that the decrease in the number and size of MPs was caused by physical effects still cannot be excluded in this study.

Nuisance odors are caused by chemical odorants. Recent studies at the Orange County Sanitation District (OCSD) at two wastewater treatment plants showed that, besides hydrogen sulfide [H2S], eight other odorants in four different family of compounds were consistently present (1). These were rotten vegetable and garlic odorants (methyl mercaptan [MM], dimethyl sulfide [DMS] and dimethyl disulfide [DMDS]), ammonia, earthy/musty/moldy odorants (2-methylisoborneol [MIB] and 2-isopropyl-3-methoxypyrazine [IPMP]) and fecal odorants (indole and skatole). The odor profile method (OPM) with a trained odor panel was used to assess these odors during dilution of the samples. The OPM uses a 7-point odor intensity scale that is based upon the drinking water flavor profile analysis (FPA), a standard method of water analysis (2). The odorous air was diluted by an olfactometer in stages from Teflon bag samples and followed by an OPM analysis to show the decrease of odor upon dilution and the appearance of masked odors. The wastewater odor wheel was used to standardize odor descriptors during the analysis, Figure 1 (3). The objective of this study was to describe a new methodology to: 1) determine the concentration at which each odorant most probably becomes a public nuisance and 2) demonstrate how olfactometry and the OPM can be used together to show masking of odorants in real life foul air samples when the samples are diluted from a source. Experimental The Odor Threshold Concentrations (OTCs) were determined by a triangular forced choice sample presentation for each odorant (4). Each panelist was forced to choose between two blanks and an odorous sample. The panelists were asked to provide an odor intensity rating during dilution of the sample by an olfactometer, using the FPA scale. The odor intensity scale is based upon the Weber-Fechner Law (4) where a single odorant's intensity is proportional to the Log of the odorant's concentration. Odor Intensity (I) = k Log (Concentration) + b Figure 2 shows the relationship between odorant intensity and the corresponding log value of odorant concentration. The red line is the odor concentration-intensity curve, which is asymptotic on both ends towards no odor and unbearable odor, respectively. The blue line is the section of the red line that obeys the Weber-Fechner Law. The odor threshold concentration (OTC) corresponds to odor intensity one (I=1) and the odor recognition concentration (ORC) corresponds to odor intensity four (I=4) for each odor when 50% of an odor panel can define the corresponding odor intensity. An action level or odor nuisance concentration (ONC) was suggested to be set at the intensity of three (I=3) to ensure action is taken before 50% of the general population recognizes the odor. Results: Odor Persistency Curves for Odorants Observed at the Wastewater Treatment Plants Figure 3 shows the OTC and the ORC of the nine persistent odorants at two wastewater treatment facilities determined by Weber-Fechner curves for each odorant using dynamic olfactometry combined with the OPM. The OTCs were within range of those determined in the literature. The ONCs have never been referenced in the literature. The odor nuisance concentration results presented here are important to odor control because they provide information defining the nuisance odorant's isopleths in modeling and avoid a public nuisance. Observing the Odor Masking Effect Observed at the Wastewater Treatment Plants Dynamic olfactometry combined with the OPM were also used with actual foul air samples from different sources. When analyzing the dilution of the initial source concentration, it was observed that the initially prominent fecal and sulfur odors gradually decreased with increased dilution (Figure 4). However, a musty odor began to gradually appear while the fecal and sulfur odors became undetectable. We named this observation the 'peeling of an onion effect'. It is apparent that this occurs because the musty odors in the foul air sample are masked by the fecal and the sulfur odors. An example of the 'peeling of an onion effect' is shown in Figure 4, which are the results of dynamic olfactometry analysis combined with the OPM. It illustrates the gradual change in odors perceived with progressing dilutions of a foul air sample of Activated Sludge Reactor at OCSD. The fecal (I=5.6) and sulfur (I=4.2) odors were initially prominent (with no musty odors reported) in the foul air. During dilution, the intensities of both the fecal and the sulfur odors decreased. At greater dilution ratios, musty odors emerged, and the other odors became undetectable, producing the 'peeling of an onion effect'. The results indicate that while fecal and sulfur odors may dominate at or near the sources, musty odors may be the primary nuisance at or beyond the fence line after some downwind distance where the public may be affected. The 'peeling of an onion effect' occurs due to the low OTCs of musty odorants; MIB (0.02 ppb) and IPMP (0.004 ppb) compared to those of fecal odorants; indole (0.5 ppb) and skatole (0.018 ppb) and sulfur odorants; DMS (3.0 ppb), H2S (0.51 ppb), DMDS (0.2 ppb), and MM (0.08 ppb). In the presence of fecal and sulfur odorants at high concentration levels, the musty odor is less perceivable unless the fecal and/or sulfur odors are 'peeled away'. Figure 4 shows that the slope of the regression line for IPMP is the most gradual, indicating that musty odors are more persistent in air because its odor intensity decreases slower with downwind dilution than the other odorants. In comparison, the fecal and sulfur odorants lines are clearly steeper, indicating a faster decrease in odor intensities with downwind distances. Thus, musty odors may cause problems at or beyond fence-line even if they are initially masked by sulfur or fecal odors at odor sources. This estimation must be verified by onsite OPM analyses at downwind distances from odor sources as atmospheric and topographical conditions will affect this behavior.