Results

This assessment and report was performed by Cameron Colby, P.E., a Master's in Environmental Engineering candidate from Clemson University and employee of Renewable Water Resources, with expected program completion and graduation on December 17, 2020. Dr. Timothy DeVol, PhD served as the primary advisor for this project. Background and Introduction Poly-and perfluoroalkyl compounds (PFAS) are an emerging category of synthetic organic contaminant first included in the EPA's Third Unmonitored Contaminant Monitoring Rule 3 (UCMR 3) in 2012 (Environmental Protection Agency, 2016). Six PFAS compounds, perfluorooctanesulfonic acid (PFOS), perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), perfluorohexanesulfonic acid (PFHxS), perfluoroheptanoic acid (PFHpA), and perfluorobutanesulfonic acid (PFBS) were named to UCMR 3 (Environmental Protection Agency, 2016). PFAS compounds have historically been used in firefighting foams and, more recently, widely used in numerous consumer items such as textiles, non-stick cookware, paper products, carpets, and cleaning materials (Hamid, 2016). Industrial uses are also prevalent, incorporating PFAS compounds into processes such as metal plating, electronics production, and photography (Hamid, 2016). At the time of this report, no studies were identified that assessed the fate and transport of PFAS from the land application of wastewater biosolids to a human receptor. It is imperative for water resource recovery facilities to be able to quantify and understand, on a scientific basis, the potential impact of PFAS contamination from the biosolid product stream as it pertains to groundwater, vegetation, livestock, and a human receptor. Where lifecycle quantification of a contaminant are not measured or modeled, managerial and operational decisions involving biosolids could be made arbitrarily or unnecessarily, leading to costly program burdens. This risk assessment sought to quantify the possible cumulative oral risk posed to a human receptor from the land application of biosolids from water resource recovery facilities owned and operated by Renewable Water Resources (ReWa). Six biosolids samples from each of four water resource recovery facilities were analyzed for the presence of PFOS, PFOA, PFNA, PFHxS, PFBS, and pentafluorobutanoic acid (PFBA), with the average concentration of each compound from each facility used in a risk assessment. Transport and fate of PFAS from the land application of municipal Class B liquid biosolids in the Piedmont region of South Carolina were modeled in one dimension using derivations of the contaminant transport equation through the vadose zone, groundwater, and vegetative pathways. Chemical partioning, diffusion, bioaccumulation, and transfer parameters were compiled from multiple peer reviewed studies. The level of impact to a human receptor was quantified as a dose in milligrams per kilogram per day of contaminant and compared to the oral chronic or sub-chronic established or proposed reference dose, where available. Summary findings Vadose zone transport velocity was found to be retarded by the compounds' calculated soil partitioning coefficients (KD), which are dependent on the fraction of organic carbon present in the soil. In general, compounds with longer carbon chains (C>7) experienced longer retardation than those with shorter chains and are expected to be present at higher concentrations in shallower soil than in deeper soil. PFOA was an exception, and the assessment predicted it reaching the groundwater table in approximately 40 years as opposed to PFOS, also containing an eight-carbon chain, which was predicted to reach the groundwater table in 128 years. Additionally, vertical transport appeared to occur more quickly than horizontal transport, which is a factor of percolation rate and can vary based on region specific rainfall amounts and soil attributes. Saturated transport below the groundwater table was less retarded than vadose zone transport, suggesting the air-water interface in the vadose zone may play an important role in a compounds' mobility. In general, and similarly to vadose transport, soil partitioning played a large role in the retardation of groundwater transport, with longer carbon chain compounds taking longer to reach a well located ten meters from the point of application when compared to shorter chain compounds. PFOA was again an exception to this pattern. Transport through the vadose zone and groundwater presented the most temporally varied behavior amongst PFAS compounds, largely due to differing organic carbon sorption behavior. Biosolid concentration levels resulted in a maximum modeled groundwater contamination level an order of magnitude below the EPA's current health advisory level of 70 parts per trillion for PFOS or PFOA, signifying a nominal risk. Groundwater consumption did not contribute to the exceedance of any oral chronic or sub-chronic reference doses. PFOS and PFHxS exhibited modeled concentration in cow's milk from the consumption of fescue and Bermuda grass on land application fields in excess of the oral chronic RfD and sub-chronic RfD respectively. PFHxS also exceeded the oral sub-chronic RfD in cow muscle tissue. This suggests that livestock and livestock products may be a source of potential exposure for utilities land applying biosolids and having those fields' products serve as feedstock or grazing space. Having a grasp of the end-use of vegetation from land application fields could become a critical component in biosolid program decisions. Additional studies are needed to firmly establish compound bioaccumulation and transfer factors. Municipalities should consider, where feasible, understanding the lifecycle of biosolid impact to local, regional, or nationally distributed livestock products, i.e. milk and meat, produced from animals fed hay and wet feed from biosolid amended fields. Model verification Soil samples in 3 locations from the field used in the risk assessment were collected to verify the model. Two six-inch core samples were taken at the outer boundaries of the field, with each separated into 3-inch sections for analysis. A third core sample was taken at the middle of the field and measured 24-inches, with analysis being conducted on 1-3-inches, 4-6 inches, 6-12 inches, and 12-24 inches. At the time of this abstract, results have not yet been returned. The expected result should verify that compounds with longer carbon chains (C>7) will have higher concentrations in the shallower samples than when compared to deeper samples, and shorter chain carbons (C<7) should be present at deeper soil depths. Final results would be incorporated into the presentation and final manuscript.

Biofiltration involves the use of biofilms to aerobically oxidize air-borne pollutants using either a packed bed of natural or synthetic media. In these cases the air-borne pollutants diffuse into the biofilm established on the biomedia surface and biodegrade, eventually forming carbon dioxide, nitrates, nitrites, sulfates, etc. The overall biological treatment rate is usually affected by this diffusion rate into the biofilm, which is part of the mass transfer process. When the air-borne concentration of the pollutant is low, as in odor treatment, this diffusive flux into the biofilm becomes the rate controlling step. This also occurs when the molecular weight of the pollutant is high, which decreases its diffusivity into the biofilm. A convective biofilter is designed to allow the exhaust gas with its air-borne pollutants to flow through the biofilm, rather than past it, and this allows the pollutant to flow through the biofilm rather than diffusing through it. This eliminates the dependance of the overall treatment rate on the diffusive flux through the biofilm while providing oxygen, carbon and nutrients into the biofilm. In this paper, experimental data on the treatment of toluene through a convective biofilter will be presented. The convective biofilter was constructed using a highly porous, ceramic, activated-carbon coated, rectangular block which had holes from one end to the other end. Exhaust gas with toluene flowed into the porous block at one end, and we closed the other end of the holes, which forced the gas through the porous walls between the holes. When the biofilms were established on these porous walls, the contaminated air was forced to flow through the biofilms adhering to the porous walls, while the media was kept moist through humidification of air using aerosolized water. The control was a Diffusive Flow Biofilter Media (DFBM) in which the other end of the straight holes were not plugged, and this allowed the contaminated air to flow through the holes while the biofilms were established on the porous walls inside each of the straight passage through the block. By using a similar size media block and the same flow of contaminated air with identical influent concentration of toluene, the CFBM filter could be compared side-by-side with a DFBM biofilter. The CFBM performed consistently better than the DFBM at a toluene concentration level below 100 ppmv, indicated by higher removal efficiency and more carbon dioxide production. Mathematical models for the CFBM were developed to better understand the processes within the CFBM biofilter and the results of these simulations for both the CFBM and DFBM biofilters agreed well with the experimental data. Results of this study will be presented in this paper.

The BlueKolding utility in Kolding, Denmark (population ~90,000) has implemented global real time control in 19 basins in the combined sewer network. The objective of the implementation was to reduce combined sewer overflows, minimize the risk of flooding in the city and at the same time reduce the needed extension of basin volume from 5,000 m3 to just 2,000 m3 to fulfill the demands and maintain the same level of service. This system has now been running, tuned and operated with success. BlueKolding has decided to take the next step and introduce cloud-based model predictive control in the system (Jess, 2018). The goal of this is to further reduce CSOs in the system, make it easier to implement and calibrate new control points, maintain the system and prepare for future developments. Background: The control algorithm used in BlueKolding, was developed in its original form during the Storm- and Wastewater Informatics project (Vezzaro and Grum, 2012; Vezzaro et. al., 2013). Since then it has been tested online and gone through several upgrades, which have added more robustness into the algorithm. The updated cloud-based control algorithm in Sewerflex is now part of AQUAVISTA, Veolia Water Technologies' global digital offer for real-time performance optimization of water treatment facilities. Methods: The MPC routine: The Sewerflex MPC routine is performing a coordinated 'smart' usage of the retention basin volumes in order to minimize combined sewer overflows. The control strategy is based on a dynamic risk assessment where the risk of overflow is calculated for every retention basin every 5 minutes, based on:

-- Actual retention basin filling and total retention basin volume
-- Predicted runoff volume from dry weather and rainfall forecast
-- The relative cost due to overflow (depending on i.e. recipient sensitivity)
-- Possible hydraulic emptying capacity of the retention basin equivalent to fixed gate position and/or pump operation
-- The actual hydraulic capacity of the downstream wastewater treatment plant.

Using a simplified model of the sewer system (Figure 1.1) together with a genetic optimization algorithm, the total overflow risk (all retention basins combined) is minimized, by changing the emptying capacities of the retention basins. The simplified model contains the retention basins, the catchment to the retention basins, the sewer connections between the retention basins and a downstream boundary (the wastewater treatment plant). By using a relative cost for overflow (cost/m3) at each location, the optimal solution - predicted optimal flows in connections between retention basins - takes into account which retention basins are more 'expensive' to use than others. This will try to locate any unavoidable combined sewer overflows at 'low cost' locations -- being the most environmentally robust locations. These settings can be changed at any time by the operator, allowing different CSO priority during the year to prioritize e.g. bathing waters and beaches in the summer time. Implementation and Operation: As the first step in the implementation, Sewerflex performance has been evaluated on 120 rain events, in an offline test environment where the MPC interacts with a hydraulic model representing the sewer network of Kolding. Performance of Sewerflex MPC is evaluated based on stability of calculated set-points and from calculated CSO volumes compared to similar calculations based on the current calibrated and tuned Sewerflex 1.0 code implemented in Kolding. In this test environment the Sewerflex MPC has improved the overall performance by approximately 10% based on CSO volume. In order to allow 'proactive' control, where the Sewerflex MPC algorithm can prepare the sewer network for future rain events before they occur (Water Smart Cities 2016), the algorithm will use both online measurements from the system, and weather forecast information. All these input data are visualized through SewerView, see Figure 1.2. As default, the SewerView map gives basic live information about the state of the sewer network, e.g. rainfall, flood risk and overflow. Following the test environment, the algorithm will be launched in 'offline cloud mode', meaning live visualization but no optimization of the sewer network. This phase of the project will allow for everyone to feel comfortable with the information given before online operation. The online operation is expected to be carried out in steps, allowing a slow transformation from the current online control to the cloud-based algorithm. The current RTC control will be kept as a fallback strategy. Further upgrades: The downstream WWTP is also upgraded to a cloud based real-time performance optimization using AQUAVISTA Plant, thereby achieving a holistic solution of a full optimized wastewater system. In dry weather, an ongoing development project (2017-2020) called 'BlueGrid' will add the functionality of flexible power consumption using demand/response at both the WWTP and sewer network, thereby achieving a flexible 'all weather optimization' which minimizes CSO during rain events and reduces costs for power consumption during dry weather (BlueGrid 2017).

1. Background Sludge treatment processes typically incorporate physical, chemical, and biological unit operations to reduce sludge volume, odour, vector attraction, and pathogens in the product biosolids [1]. Biosolids are regulated with respect to pathogen, nutrient, and heavy metal content if land applied [2]. However, biosolids may also carry a wide range of anthropogenic chemicals such as pharmaceuticals, personal car e products, surfactants, plasticizers, flame retardants, and water and stain resistant coatings [3], collectively called emerging organic contaminants (EOC). The presence of trace levels of EOCs has been identified as a concern associated with their land application as they could potentially mobilize into soil, infiltrate into ground water, or be uptaken by vegetation [4]. While the long-term risks of exposure to humans are relatively unknown, some of the EOCs are known to be toxic, persistent and bioaccumulative [3,4]. Hence, an understanding of the occurrence and fate of EOCs in sludge handling systems that produce biosolids will provide a basis on which risks can be quantified. Further, most studies pertaining to EOCs and wastewater solids only document the contaminant presence in the product biosolids and there is little information on their removal through sludge processing systems. Further, the relative performance of different physical, chemical and biological sludge treatment processes is also largely unknown The objective of this study was to study the behavior of five major classes of EOCs: per- and poly-fluoroalkyl substances (PFAS), polybrominated diphenyl ethers (PBDE), alkyl phenols and ethoxylate derivatives, bisphenol A (BPA), and triclosan in common sludge treatment systems. The final paper will highlight the key findings from this multi-plant study and discuss the practical implications for biosolids management practices. 2. Study Design Samples of raw sludge and the final stabilized biosolids were collected from nine sludge treatment systems that included pelletization (P), alkaline stabilization (AS), aerobic digestion (AE1 and AE2) and anaerobic digestion (AN1 to AN5) processes. Grab samples were collected in glass jars on three consecutive days within a one-month period in each of 2015 and 2016 and shipped overnight on ice to the lab for contaminant analysis. The target analytes included 13 PFAS, 21 PBDEs, 4 alkyl phenols and ethoxylate derivatives, BPA, and triclosan. All the EOC analyses were conducted by SGS AXYS International (Sidney, BC) following stringent quality control procedures. 3. Major Findings The measured concentrations were used to estimate contaminant mass flows (mg/day) in and out of the system (contaminant concentration ng/g x solids flow kg/day) to assemble contaminant mass balance through the system. Percent removal was then calculated to evaluate the relative performance of the treatment systems. An overview of five major findings from this study are subsequently presented. A detailed discussion on the influence of the contaminant and treatment plant related factors will be included in the final paper. 3.1 All types of sludge treatment lead to EOC removal: While sludge treatment systems are primarily designed to prepare biosolids for subsequent disposition, the results of this study suggest that some removal of EOCs also occurs during the process. Up to 87% removal of triclosan was observed in AE2 during aerobic digestion. Nonylphenol monoethoxylate and diethoxylates were removed in both aerobic (Mono: 59 to 86%; Di: 84 to 95%) and anaerobic digestion (Mono: 35 to 79%; Di: 69 to 96%). Alkaline stabilization, where the raw sludge was stabilized at high pH using lime and cement kiln dust, was effective in reducing ΣPBDE mass flows by 53 ±12%. During pelletization, where the raw sludge was thermally dried and compacted, there were low removals of perfluorodecanoate (PFDA) (17%) and ΣPBDE (6%) mass flows. Hence, all treatments resulted in some degree of contaminant removal but removals differed between technologies. 3.2 Contaminant formation is possible during sludge treatment: The conditions established in sludge treatment can also lead to transformation of contaminants resulting in an increase in mass flows through the systems. Such an effect was commonly observed for selected PFAS where the average mass flow of the measured compounds increased by 59%, 19%, 2%, 264%, and 13% in AS, P, AE1, AN1, and AN5, respectively (Figure 1). Further, a net increase in mass flow of 4-nonylphenol was consistently observed in all five anaerobic digestion systems. Evidence of reductive debromination of fully brominated PBDE congeners into partially brominated PBDE congeners was also seen in anaerobic digestion systems. Thus, sludge treatment systems can transform precursors to increase contaminant mass flows through treatment. 3.3 Removal is dependent on sludge feed characteristics: The raw sludge fed to sludge treatment processes can differ because of differences in the inputs of contaminants to the sewershed and in the types of wastewater treatment processes generating the sludge. EOC use and release in a given sewershed will be reflected in the contaminant loading from the sludge treatment process. For example, BPA was measured in the raw sludge in all treatment systems except AE2. Since BPA was not detected in the raw sludge at AE2, this substance was also not detected in the biosolids at this treatment system. Differences in upstream wastewater treatment processes design can also impact the EOC content in the final biosolids. For instance, the biosolids where the raw sludge was predominantly composed of primary sludge had less diversity in overall PFAS composition compared to blended raw sludge feeds (primary and waste activated sludge) where a wide variety in PFAS composition was observed. Hence, differences in raw sludge properties were found to impact the biosolids quality following treatment. 3.4 Removal is dependent on the type of sludge treatment: The target compounds behaved differently in physical, chemical and biological treatments leading to different final biosolids quality. For example, while alkaline stabilization was effective in removing PBDEs, anaerobic digestion led to an increase in PBDE mass flows. In addition, the behavior of perfluorodecanoate (PFDA) differed between treatment systems with responses ranging from moderate removal (41%) to substantial formation (-264%). Even in the studied biological processes, there were distinctions between aerobic and anaerobic sludge treatments. For example, PFOA had low levels of net removal (< 25%) during anaerobic digestion (AN3 and AN5) and contrarily a net increase in mass flow by -68% and -282% in aerobic digestion systems (AE1 and AE2 respectively). The differences in transformations was found to impact the final biosolids quality. 3.5 Removal is dependent on the plant operations: Site specific factors, especially in biological treatment systems, such as the solids retention time, staging of the treatment processes and the active microbial consortia appeared to impact contaminant fate through treatment and hence biosolids quality. For instance, BPA was removed in AN2 with an average efficiency of 75% whereas formation of BPA was seen in other anaerobic digestion processes (AN1, AN4 and AN5). In aerobic digestion, there were low levels of average removals of perfluorohexanoate (PFHxA) (28%) in plant AE1, whereas AE2 reported low average levels of formation (-11%). A detailed discussion on the site-specific factors and operating conditions that may be responsible for the observed removals and biosolids quality will be presented in the full paper. 4. Significance of the findings This study evaluated contaminant loadings and removal of five major classes of EOCs namely PFAS, PBDEs, alkyl phenol, BPA, and triclosan in different full scale sludge treatment systems. The lessons learned will benefit all stakeholders of the biosolids industry in understanding the responses of EOCs thorough sludge treatment. The removal efficiencies presented in this study will enable the treatment plant managers to appraise the performance of sludge handling systems with respect to EOCs. The contaminant loading estimates could be used to communicate the significance of biosolids quality to end users. Further, there is little information describing contaminant mass balances and overall removal through sludge treatment. This study bridged this critical knowledge gap and addressed major questions related to PFAS, PBDEs and phenolics in physical, chemical and biological sludge treatment processes.

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

The City of Houston is the fourth largest city in the nation. Houston Water within the Houston Public Works department operates and maintains a large water and wastewater system. Its wastewater system includes approx. 39 treatment plants (WWTP) with a combined permitted capacity of 564 MGD, 5900 miles of sewer pipes, 127,000 manholes, and 385 lift stations spread out over 650 square miles to serve about 2.3 million customers. City of Houston's 311 Call Center receives an average of 1800 wastewater customer complaints per month. Issues may range from odor complaints, cave-ins to sewer backups in bathtubs. Houston Water is responsible for addressing these issues by mitigating the impact on public health and environment. Houston Water has a long history of using state-of-the-art technologies for managing its huge water and wastewater infrastructure. For Wastewater, it relies on systems such as; Infor IPS to manage work orders, service requests and tracking SSO records, HachWIMS to manage regulatory reporting, Infor EAM for facilities work order management and Enterprise GIS to support asset management for collection system. Recently, Houston Water introduced ArcGIS Online and Business Intelligence Tool, Power BI in every aspect of full-cycle process- starting from receiving customers call to satisfactory resolution of the problems.

THE PROCESS
Initial Call It all starts when a possible SSO is reported to the City of Houston's 311 Call Center. The 311 operator generates a service request (SR) which is logged into the Infor IPS. Once a service request is initiated, the clock starts ticking for the first responders, wastewater inspections team to respond to the request. Depending on the type of request -- a priority level is assigned to each Service Request. As an example- 'High Priority' is assigned to an active SSO that is threatening to enter a storm drain. A 'Medium-Priority' may be assigned to an odor complaint. First Responders Wastewater inspectors are equipped with a tablet to notify them of newly created SR through Infor IPS dashboard and also to enter field data into the Infor system. Inspectors are responsible to identify the type of SSO- Public or Private, where it occurred, the volume, flow rate, status of manholes upstream and downstream of the incident location and the possible cause. Inspectors create an SSO incident in the Infor platform for the stoppage team to take further action. The start times and flow rate data are recorded in real-time and cannot be edited to maintain the integrity of data. Stoppage team- Further Investigation Stoppage team are equipped with jetting and vacuum trucks to clear a blockage, stop the SSO, clean and disinfect the area and report the confirmed cause of the SSO. Stoppage crew is also equipped with tablets to enter details of SSO such as confirmed cause, actions taken to mitigate the SSO, and request for work orders. Depending on the needs work order could be issued for televising the line or installing bypass pumps. Quality Checking the Data for Regulatory Purposes Data is validated and confirmed in a weekly SSO meeting before weekly reports are sent to State Regulatory Agency- TCEQ. The meeting is attended by various stakeholders that includes regulatory team, inspection and stoppage team, customer service and Houston Health Department (HHD). ArcGIS Online and Power BI Dashboards provide the real-time and historical reference information. Recurrence Prevention through Analysis Greater than 70% of all public SSOs are preventable SSOs as they are caused by the accumulation of grease and rags/non flushable wipes in the sewer pipelines. Repeat SSOs are plotted on a dynamic ArcGIS map to identify SSO hot spots. This makes it easier for the wastewater analysis group to target high priority areas for Preventive Maintenance (PM) cleaning. A sample hotspot snapshot is shown in Exhibit 1, which illustrates the effectiveness of the PM cleaning program by reducing the preventable SSOs from 63 SSOs in 2018 to 29 SSOs in 2019.

Tracking Wet Weather SSOs
SSOs are also caused due to hydraulic capacity constraints in the collection system. Power BI is used to track the high volume (over 100,000 gallons) and number of repeat SSOs (3 or more) occurred during wet weather in previous three years in one manhole, as shown in Exhibit 2. This information is used to develop a capacity remedial measures plan. Fats, Oil and Grease (FOG) Program Houston Water's FOG outreach group uses ArcGIS Online based tool for targeted campaigns. HHD administers FOG Generator Interceptor Inspection program. HHD maintains a database for the Grease Trap inspections that are used by the FOG Outreach group to identify target areas that includes apartment complex and Food Service Establishments. Both, HHD and FOG outreach group use similar density maps as seen in Exhibit 1 for their respective needs. Intelligent Manhole Covers Houston Water uses intelligent manhole covers to provide real-time water levels to pro-actively detect a potential SSO that helps to mobilize maintenance crews to prevent SSOs from occurring. The continuously monitored manhole covers provide information to determine the rate of accumulation of debris in the pipes that eventually helps to develop PM cleaning program. The data from the manhole covers along with the lift station SCADA data are also used for verification of the collection system hydraulic models. Business Intelligence software such as Power BI and ArcGIS Online Dynamic mapping tools are used to efficiently process, visualize, analyze and share the outcome to present in a meaning way to effectively use the resources. The experience and effectiveness of using these emerging techniques and technologies, some of which are free, would be beneficial for water and wastewater utilities of all sizes.

Designing odor control systems for operation in cold weather climates requires additional considerations to ensure success. Overlooking these details can lead to decreased performance and even failure. Webster Environmental Associates (WEA) has been designing and testing odor control systems throughout the country for over 35 years and we've learned a number of lessons along the way. This presentation will provide a road map for evaluating the potential effects of cold weather on odor control systems and will include the following: -Seasonal effects on odor control loading -Odor control technology comparison for cold weather conditions -Estimating inlet air temperatures -Freeze protection options -Adjusting airflows for seasonal changes -Backup power supply requirements -Startup issues in cold weather -Provisions for re-acclimation of biological systems This presentation will include case studies and lessons learned. One case study that will be included in detail is a recent project located in Michigan that WEA designed with Tetra Tech. The design of this project was completed in 2018 and construction was completed in 2019. This project included the design and installation of a 9,000 cfm carbon adsorber and a 10,000 cfm bioscrubber. The carbon adsorber treats air from a series of rotating biological contactors (RBCs) and the bioscrubber treats air from primary clarifiers, a septage receiving facility, headworks, a grit facility, sludge storage tanks, and a series of channels. The first challenge of this project was that the client requested that the system be able to continually operate at ambient temperatures of -20 °F which was the historic low for the area. This requirement caused us to take a closer look at what the inlet temperatures to the odor control systems could be at this condition. We went back to the site during very cold weather and took temperature readings at the different sources. One of our surprise findings was that some of the channels didn't always have water in them, especially in the middle of the night when flows were low (and of course this would be the coldest time!). During that condition, the temperature of the air coming from the channels would be near the ambient temperature. We had a mechanical engineer on the team conduct heat loss calcs based on the data we collected and he determined that the inlet temperature at the bioscrubber could go below freezing when the ambient temperature is -20 °F. We evaluated multiple solutions, including an inline heater, capturing waste heat from another source, etc. In the end the most cost-effective solution was to provide an auxiliary heat source that would add heat into the primary clarifier (see Figure 1 below). This option was the least expensive as it utilized a standard makeup air unit (MAU). The MAU would be controlled by the bioscrubber control panel and only come on when needed. The below is an excerpt from the specified control logic: The MAU shall provide additional heat to the foul air system when the inlet air temperature goes below 36°F. Bioscrubber shall send signal to MAU to turn it on. The bioscrubber will turn off the MAU after 4 hours and re-evaluate the inlet temperature. If the inlet temperature again falls below 36°F, then the bioscrubber will initiate the MAU again for another 4-hour cycle. This cycle will continue until the inlet air temperature remains above 36°F without the MAU.
The next challenge that we faced was the significant seasonal fluctuation in hydrogen sulfide (H2S) levels. Prior to initiating design, WEA conducted an odor study which included two rounds of testing, one in the cool weather and one in the warm weather (see Figure 2 and 3). The results of the testing revealed that H2S averaged 34 ppm during the warm weather testing and 5 ppm during cool weather. However, we did some additional spot testing as design was proceeding during colder weather (in February) to verify loadings and found that the H2S actually drops below 1 ppm throughout facility during the winter. This created a challenge as the bioscrubber may struggle to stay acclimated over the winter, depending on how long the H2S stays depressed. In order to address this potential issue, the design required that the system have the ability to operate in a once-through or recirculation mode without any modification of piping or the addition of any equipment. If needed, the bioscrubber could easily be switched over to a recirculation mode temporarily in the spring to allow the bioscrubber to re-acclimate.
Several other hurdles were also encountered, including the need for the duct to be insulated and acclimation during the early spring. These will all be discussed in detail in the presentation. In addition to the Michigan project, we will also be presenting lessons learned from other projects in cold weather climates as time allows. Additionally, an overall comparison will be made between different odor control technologies operating in cold weather and provisions that need to be made to ensure efficient performance.

Air pollutants such as hydrogen sulfide and reduced sulfur compounds (RSCs) are a common by-product of wastewater collections and treatment. The transfer and processing of wastewater causes turbulent conditions which releases these odorous and corrosive compounds into the air. As development encroaches on wastewater treatment plants and pump stations, complaints from nearby residents and businesses are on the rise. In order to protect public health, quality of life and valuable investments in infrastructure, municipalities must develop strategies for controlling the release of these compounds. In recent years, the biological treatment of hydrogen sulfide and RSCs has become one of the primary methods for controlling odors and corrosion resulting from wastewater collections and treatment. The most common biological treatment technologies include biofilters and biotrickling filters. This presentation analyzes the unique features of each technology and introduces ways in which these biological treatment methods are now being combined into hybrid systems to improve performance and reduce life-cycle costs. A detailed analysis of multiple types of filtration media will be provided. Media types will be evaluated on such factors as cost, surface area, porosity and sourcing. An increased focus will be placed on recycled sources of filtration media. These types of media are in increased demand due to the favorable cost, availability and sustainability associated with them. Case studies will be presented comparing traditional and hybrid technologies on such metrics as odor removal efficiency, energy usage, filtration media type, water demand and nutrient addition requirements. Life-cycle analyses will be introduced to compare each technology on projected capital and operational costs. Operation and maintenance requirements for odor control systems vary widely and are often overlooked in the design process. Analyses of these requirements will be compared and presented as well. This presentation concludes with a survey of new innovations in biological odor treatment. Topics include microbiome DNA testing, smart controls and sustainable odor control systems.

Population growth brings capacity issues, climate change brings increased frequency and intensity of storm events, and ongoing system blockages from FOG result in overflow conditions that impact our communities and the environment. Municipalities are subject to ever-tightening regulatory oversight where high cost consent decrees for sanitary sewer overflows (SSOs) and combined sewer overflows (CSOs) are becoming the norm. The typical response is expensive capital upgrades to collection system infrastructure and high frequency cleaning of collection system segments on a schedule. Faced with uncertainty, municipalities are staring down the prospects of significant infrastructure investments and billion-dollar consent decrees to protect residential property, local businesses and waterways -- without a significant increase in resources. Despite the potential penalties and the prospect of massive capital projects, the benefits they may produce are decades in the making and consume billions of dollars of municipal revenue. It is imperative, then, that we begin to understand the real-time operation of our existing collection system infrastructure to maximize utility, minimize costs and target investments to the appropriate and highest risk areas. For more than 500 sewers around North America, the solution involves innovative turbo charging of their collection system engine to take an aggressive stance on risk management. A data-driven early warning system designed combines a real-time view of the sewer and stormwater networks, weather and storm data and real time notifications allowing them to be proactive in responding to conditions and detecting emergencies before an overflow. Those who attend 'Turbocharged Engines' will learn how agencies of varying size are using real-time sewer monitoring technology to provide actionable information in order to protect the environment, safeguard public health and optimize investments in maintenance and capital improvements. Many collection systems adhere to the EPA's comprehensive capacity assurance, management, operations and maintenance (CMOM) programs to prevent CSOs and SSOs. Such measures include backup pumps, frequent cleaning in high-risk areas, capital projects and flow reduction measures that maintain the pipes at their design capacity. While these programs can be effective, they often do not allow utility staff to be proactive – particularly in the face of rapidly evolving events. To provide that next level of understanding, control and response, three cities in Texas turbocharged their sewer intelligence with real-time visibility into the status of their underground infrastructure. These municipalities deployed a network of SmartCover systems to provide real-time sewer level and trend analysis information to a centralized, online dashboard and mobile app. Designed with the unique challenges of a collection system in mind, the technology transmits data from a sensor in the manhole to a satellite in the sky to relay reliable sewer information throughout all conditions – a particular benefit in places like Texas where weather events can often disrupt terrestrial communications. The patented sensors are purpose-built to withstand the harsh conditions in sewer systems and can be installed and serviced without confined space entry. SmartCover provided each utility with an event management platform with localized weather data from the National Oceanic and Atmospheric Administration (NOAA) to rapidly respond to issues before they become environmental, public health and financial emergencies. This system architecture has revolutionized the utility's response, allowing changes in conditions to be monitored in real-time, while reducing the uncertainty around the conditions in the network. Knowing the level trends in the sewers has helped the utilities schedule maintenance when and where it is needed most, and more importantly has been critical in preventing overflow events. SILENT SENTRIES PROTECT ENVIRONMENT The City of San Marcos, TX, treasures the San Marcos River, a spring-fed river winding 75 miles providing a critical habitat for eight endangered species. Further, the region is of significant archaeological interest as one of the oldest continuously inhabited places in North America. Given the river's rich history and central role in the city, its protection is a primary focus. Yet, extreme weather events are making this increasingly difficult. Solution: To preserve the local waterways during extreme weather events, the city installed 10 SmartCover monitors in high risk spots and outflows. Results: Automatic advance notification of blockages has helped the city mitigate SSOs and monitor and report on CSOs, adhering to the Texas Pollutant Discharge Elimination System Small Municipal Separate Storm Sewer (MS4) requirements. SSO MITIGATION SEES IMMEDIATE ROI Heavy rain events contribute to sewer overflows in the City of Arlington, TX, damaging property, the environment and impacting public health. Solution: Installation of 10 SmartCover sensors and rain monitors to measure flow in typical sewer trouble spots. This event-driven system allows staff to react to any blockages and other potential overflow conditions before wastewater backs up into homes and businesses or overflows the system. Results: In the first few months, the City of Arlington was notified of three alarms that helped avoid sanitary sewer overflows-- more than paying for the systems in a short period of time. After a presentation to City Council, the initial deployment was expanded to 60 SmartCover units using NOAA rain data. CLEANING PROGRAM OPTIMIZATION RESULTS IN SAVING 95% San Antonio Water System was facing an EPA Consent Decree with an estimated cost of $1.2 billion. SAWS adopted the EPA's CMOM guidelines and instituted high frequency cleaning for their 110,000 manholes and pipeline segments. Effectively this meant SAWS established a program of cleaning high risk pipes with potential for overflows, and instituted routine cleanings at monthly, bi-monthly, quarterly, semi-annual and annual frequencies. As conscientious sewer operators, SAWS identified 200 high risk sites for regular monthly cleanings – whether the pipes needed cleaning or not. While prudent, the logistics, labor and equipment costs to maintain this level of effort was staggering. Solution: SAWS deployed 200 SmartCover sensors to collect data. SAWS effectively transitioned from a routine, calendar-based cleaning system, to a prescriptive 'as needed' cleaning program when automatically notified of blockages. Results: SAWS has experienced a 95% reduction in cleaning, ZERO SSO incidence and 216 SSO 'saves.' Nearly 1,300 cleanings were scheduled, but only 65 cleanings were identified and performed -- an estimated $1 million in savings. By trusting automated data analysis, the optimized maintenance schedule has led to significant positive benefits for the operator, environment, and communities served. Not only is SAWS effectively reducing wear and tear on pipelines from the routine cleaning, it's also allowing their operators to refocus on other pressing activities. CONCLUSION Operators in the City of San Marcos, City of Arlington and City of San Antonio have successfully turbocharged their collection systems with innovative technology. All cities reported reduced overflows and costs. These 24/7, silent sentries have brought peace of mind knowing sewers are being monitored, data is automatically analyzed and plenty of advance notice will be given.

This presentation shares the unique journey undertaken by the Manasquan River Regional Sewerage Authority (Authority) to understand the odor and corrosion issues in their system and the systematic steps taken to study, sample, evaluate, and select a holistic solution. The project is divided into three phases: Study, Chemical Trial, and Design Phases. During the Study Phase, air and wastewater hydrogen sulfide (H2S) data was collected and a triple bottom line (TBL) evaluation was performed to recommend potential improvements for odor and corrosion control. Results from the Study Phase indicated that the Authority’s system is generally functioning well, but there are hot spots in the system that need to be addressed locally. These locations were the focus of the TBL evaluation, which evaluated three alternatives using economic, social, and environmental criteria. The recommended alternative was evaluated during a three-month Chemical Trial that showed that the Authority’s systems can be treated effectively using calcium nitrate (i.e. Bioxide) and/or hydrogen peroxide (H2O2) to reduce H2Sand dissolved sulfide concentrations. As of March 2021, the Study Phase and Chemical Trial have been completed and the Design Phase is in progress. Calcium nitrate systems will be implemented at two meter chambers within the Authority’s system. A technology evaluation was completed for implementation of odor control systems to mitigate odors and corrosion at two pump stations. A new carbon column system will be implemented at Upper Manasquan Pump Station (UMPS)while a high plume up-blast exhaust fan will be implemented at the Lower Manasquan Pump Station (LMPS). Civil, process, structural, mechanical, electrical, and instrumentation and controls components were included in the designs.

The purpose of this presentation is to describe how a Great Lakes community is addressing its goals of reducing overflows and basement flooding while enabling real time control of its wastewater system. Peel Region believes it will require best in class measured and predictive rainfall data, to create efficiencies for conveyance and treatment, that will allow the Region to face the unique challenges of climate change, population growth, and aging infrastructure. Peel has implemented the program described in this abstract, in its 2020 Water and Wastewater Master Plan for the Lake-Based Systems. The Region of Peel, Ontario (Peel or Region) is responsible for the operation and maintenance of the sanitary sewer network, pumping stations, and wastewater treatment plants within its collection system. Peel is composed of the Cities of Brampton and Mississauga and the Town of Caledon that drain a combined surface area of 1,246 km2 to Lake Ontario. Wastewater services are also provided by Peel to neighboring Toronto and York through inter-regional servicing strategies, thus making accurate rainfall over Peel and for neighboring jurisdictions of increasing importance for managing wastewater flows. Wastewater is conveyed by gravity, generally from north to south through the collection system to the wastewater treatment facilities at Lake Ontario. Peel provides wastewater system services to Mississauga, Brampton and parts of Caledon. Demands are placed on the wastewater system because Peel is one of the fastest growing municipalities in Ontario, in excess of 1.4 million people. The Region's wastewater system comprises two principal trunk systems: the west trunk system that conveys flows along and near the Credit Valley to the Clarkson Wastewater Treatment Plant, and the east trunk system that conveys flows along and near the Etobicoke Creek Valley to the GE Booth Wastewater Treatment Plant. Planned construction of a 11-km of the East to West Diversion Trunk Sewer will require RTC and forecast precipitation. There are over 3,600 km of wastewater pipes in Peel, with 300 km of trunk sewers consisting of pipes ranging from 750 mm to 3,150 mm in diameter, servicing 294,000 customer accounts. Climate change and population growth continue to put pressure on the wastewater system. Recently, a climate change mitigation strategy was endorsed by the Region of Peel Council to reduce basement flooding due to sewer backups. Understanding system response to rainfall and taking proactive measures to reduce I/I are strategic actions aimed at reducing flooding issues region wide, and to maintain wastewater treatment capacity in the long-term. The flash flood that occurred on July 8, 2013, had a larger impact on the Region of Peel and City of Toronto than any storm since Hurricane Hazel (1954), and reinforced the need for better preparation and operation of the wastewater system. The Region is seeking to improve the wastewater system for future growth, achieve cost efficiencies, derive environmental benefits, and to lower the risks to human health. Improved rainfall monitoring, both current and forecast, are key to achieving these goals: increasing volume of wastewater treated; reducing incidents of overflows/basement flooding; and achieving effective operation of real-time controls. These goals can be more efficiently achieved through accurate and representative rainfall monitoring. This is achieved through the combination of weather radar and rain gauges. Radar-based precipitation measurement that relies on both gauges and radar is called GARR, or gauge adjusted radar rainfall. The target region and neighboring weather radars (both Canada and US) are shown in Figure 1 with range rings indicating coverage distance. Current and forecast rainfall is needed to meet the Region's objectives. Technical details on forecast rainfall is not discussed here but will be presented along with GARR during the presentation. The GARR system embodies both near-real-time (NRT) and End-of-Month (EOM). During EOM, Quality Control (QC) of rain gauges and radar removes or mitigates radar anomalies and erroneous or inconsistent gauge measurements. Gauges identified as consistent are used to bias -correct the radar precipitation rates. Thus, GARR is the combination of two sensor systems that results in better maps of rainfall than either sensor system could produce alone. GARR provides coverage of targeted areas at spatial and temporal resolutions commensurate with the sewer catchments. GARR is needed for better understanding and modeling of:

-- Basement flooding from both Sanitary Sewer Overflows (SSO) and Combined Sewer Overflow (CSO), and Facility By-Pass
-- Inflow and Infiltration Calculations
-- Hydraulic model calibration
-- Stormwater flood modelling

To illustrate the properties of GARR required by the Region, we summarize the characteristics of the extreme event, July 8, 2013. GARR was produced with weather radar and rain gauges from multiple networks from Region of Peel (29), City of Mississauga (14), and Credit Valley Conservation (13). Figure 2 depicts the spatial distribution of rainfall depth depicted by the color scale ranging 11.9 - 138.3 mm with a mean of 65.3 mm over the target area. Rain gauges are shown by black triangles with depths in mm. The scatter plot in Figure 3 shows bias-corrected radar (note 1:1 line) versus rain gauge depths for a selected period. Gauges excluded are shown in red, whereas rain gauges that pass QC (included) are shown in blue. Quality control removes bias in the GARR rainfall estimates, and generally improves accuracy from more than ± 20% to less than ± 5%.

Benefits of Presentation
This presentation should be selected because it shares the experience and challenges faced in characterizing rainfall. While GARR is an accepted technology in wastewater, the needs in the Great Lakes Region are unique and would benefit other communities with similar climate and population/development pressures.
Status of Completion
At the time of submittal this project is complete in terms of setup and operations. Historic data analysis was completed for requested storm events in March 2019. End-of Month quality-controlled GARR for all storms in May to November 2019, was completed in April 2020. Continuous production of Forecast and NRT GARR is operational beginning April 2020, and EOM GARR production continues.

Conclusion
Besides climate change, growth will continue to place pressure on water and wastewater infrastructure in Ontario. GARR is fit-for-purpose and helps address objectives of the 2020 Water and Wastewater Master Plan for the Lake-Based Systems.

INTRODUCTION
The Albuquerque Bernalillo County Water Utility Authority (Water Authority) owns and maintains over 2,000 miles of pipes in the collection system to convey approximately 50 MGD wastewater from the service area to the Southside Water Reclamation Plant (SWRP). The Water Authority has implemented a range of methods and technologies for controlling odors and corrosion in the collection system, resulting in significant institutional knowledge and experience of this branch of engineering science. Nevertheless, the sewer network still faces corrosion challenges due to sulfide generation with numerous pipes that are at risk of collapse. Comprehensive analysis of a complex collection system to allow for the optimization of sulfide control relies on the understanding and quantification of the processes impacting sulfide production and release (Revilla et al, 2016). To facilitate this intricated task, properly implemented sewer process models become a valuable tool. This implementation could also support the evaluation of the impacts of the sulfide control strategy on the SWRP process performance. The objective of this project was to marshal and organize the resource expenditure on odor and corrosion control so that it is optimized, coordinated across the collection system, and harmonized with the pipe rehabilitation program and the identified operational constrains of the SWRP. A novel approach using sewer process model (the WATS model) was implemented to develop a comprehensive sulfide control strategy, and to empower the Water Utility with a tool to support the migration from a reactive to a proactive approach on asset management while being able to communicate to SWRP staff the potential impacts in the treatment process.

METHODOLOGY
The study area for the Water Authority collection system included approximately 250 miles of pipe with a minimum diameter of 15 inch in four main interceptors (plus tributaries). A sewer process model was used to apprehend the study area as a whole and analyze physical, biological and chemical processes bearing on odor and sulfide corrosion. Data Collection. The Water Authority collected data on several parameters as part of the regular monitoring program for the collection system in 17 locations and the influent to the WWTP. These included grabs samples for wastewater temperature, pH, total and dissolved sulfide, total iron and continuous monitoring of headspace hydrogen sulfide. Additional monitoring at each of the most downstream location in the four interceptors was performed. Sewer Process Modelling. The WATS model (Hvitved-Jacobsen et al, 2013) was selected as the most appropriate software tool for this purpose. WATS is currently the most rigorous and complete sewer process model in the world and is well suited to assessing the Water Authority sewerage. The model was set up using the existing hydraulic model of the system and considering the operation of the collection system at the time of the selected calibration period in terms of flow diversions and chemical addition. Considerations for the optimization strategy in the collection system were in place to prevent negative impacts in the SWRP: 1) a minimum pH of 7 in the plant influent needed to meet the permitted effluent pH; 2) a maximum magnesium concentration in the influent to prevent formation of nuisance struvite (impacts use of magnesium hydroxide); 3) a limit in the use of solids produced in the potable water treatment plant that have the potential to be used for sulfide control if discharged to the collection system.

RESULTS AND DISCUSSION
Model Calibration The WATS model for the Water Authority collection system was calibrated to dissolved sulfide and headspace hydrogen sulfide in the 17 monitoring locations throughout the four interceptors. In addition, diurnal pH data was available to refine model calibration. Data for winter and summer were available and seasonal models were developed to allow for a more detailed strategy for optimizing sulfide control. Stochastic simulations (n=100) were run and the results compared to the complete data set for the calibration period. Figure 2 shows measurement-model agreement for station 10. Alternatives analysis for sulfide control optimization The calibrated WATS model allowed for the screening of a wide range of alternatives, including chemical dosing at various dose rates using different chemicals at various locations, and assisted in the prioritization of pipe rehabilitation given the relative cost of on-going chemical treatment versus rehabilitation. The screening resulted in novel and the most cost-effective strategies with potential to be implemented in each of the four major interceptors. Some of this approaches include: Addition of iron-rich water treatment plant solids. The San Juan Chama Water Treatment Plant can discharge residual sludge containing high levels of iron for sulfide control in the collection system. Bench-scale testing provided the input to the WATS model in terms of sulfide removal efficiency. It was determined that the amount of solids the SJCWTP was limited to discharge to prevent negative impacts at the SWRP was enough to provide comprehensive treatment for the Edith Interceptor and partial treatment at the Valley Interceptor. Comprehensive treatment at the Valley Interceptor was achieved by dosing Iron for the upstream end and by applying PRI-SC to reach sulfide control at the downstream end of it, providing the most cost effective approach. Iron addition with pH adjustment and Peroxide Regenerated Iron for Sulfide Control (PRI-SC). An evaluation was performed using the WATS model combining chemical dosing for a synergistic and cost-effective interaction between Mg(OH)2, ferric and PRISC. As shown in Figure 2, the Westside Interceptor relies on iron addition in the upstream end of the system with pH adjustment using Mg(OH)2, recognizing that sulfide precipitation rate increases as pH approaches 8 units (Hvitved-Jacobsen et al, 2013). This treatment targeted Station 64 where the PRISC process allowed for a more cost-effective solution to achieve comprehensive treatment to the nearest pump station. In addition to considering the limitations set by the SWRP influent characteristics to protect plant operation, a qualitative assessment of the impacts of the optimized strategy on the performance of the SWRP resulted in potential benefits to sulfide control in the solids train; SWRP better prepared for potential stricter phosphorus limits; and) an increase in soluble substrate for enhanced BNR. The optimization routine using WATS resulted in chemical selection and dosing maximizing existing infrastructure while maintaining wastewater characteristics in the SWRP influent within the constrains identified by plant operations.

CONCLUSION
The careful implementation of the WATS process model to the Water Authority collection system allowed for the understanding of the processes bearing in sulfide production and release, and for the screening and identification of alternatives for controlling sulfide in the system as a whole and in an optimized manner. The results confirmed that the presented methodology allows for the incorporation of modelling tools in the decision making for management of collection systems.