Results

The City of Los Angeles is home to the most innovative infrastructure solutions in the world. Sustainability and environmental stewardship are at the core of actions taken daily to service the diverse community. Diversity in the city of Los Angeles gives the City (entity) access to a rich range of talent, representing different experiences, perspectives, and styles. These differences foster a collaborative and innovative work environment that makes industry stronger and a better organization on every level. DEI goals are both internal to the City as an organization and external with workforce development and business relationships. In order to meet the DEI goals set forth by the Mayor and LA City Council leadership, the City initiated various programs. This paper explores three programs in which public agencies partner with private industry to further advance DEI goals within the external workforce industry. In order to achieve the desired diversity our industry seeks; it is important to develop thoughtful outreach events that provide the opportunity to engage with local Minority/Women-Owned Business Enterprises (MWBE) where they are at. Equally challenging is staying connected with industry during COVID virtual environment. To stay connected and increase the participation and business opportunities with the Los Angeles MWBE community, City of Los Angeles has created specific programs. - Accessing LA is the flagship contracting and business networking event of the City of Los Angeles hosted virtually to share information and resources on how to do business with the City. The event aimed to offer MWBEs an opportunity to learn about business opportunities in the Greater Los Angeles area. Specifically, the partnership aimed to provide MWBEs with information on upcoming business opportunities in the Los Angeles Area, information on Tetra Tech and their disadvantaged business partnering programs and provide the strengthened message that Los Angeles leadership is committed to growing diverse business partners in the area. - Small Business Advisory Council hosted by Bureau of Public Works Commissioners' Aura Garcia and Mike Davis. The council consist of MWBE representatives, large prime contractor representatives, and public agency representatives. The council is focused on meeting regularly to address key issues that present challenges to growing the diverse industry base in the area. The council aims to share key procurement initiatives, make connections for business partnerships, and develop working solutions to industry challenges. Tetra Tech is an active participant in the council and provides input on growing MWBEs. - Small Business Academy hosted by the Department of Public Works Bureau of Public Administration. The L.A. Small Business Academy is a 7-session course that is made possible by the collaboration of the Department of Water & Power (DWP), the Port of Los Angeles (POLA), the Los Angeles World Airports (LAWA) and the Department of Public Works (DPW). The Academy was initiated to engender the growth, sustainability, and success of small business enterprises through the provision of courses that provide direct information and insight about marketing, financing, insuring, and working on design-build, and other future projects. The completion of an extensive program focusing on empowering and preparing small, women, minority, and military veteran-owned firms. Tetra Tech partnered with the academy to host an outreach event. These initiatives are proving successful at efforts to grow a diverse business base in Los Angeles.

The Washington Suburban Sanitary Commission (WSSC) is in the process of implementing a Bio-Energy project to thermally hydrolyze and anaerobically digest all biosolids from their five Water Resource Recovery Facilities (WRRFs) to produce a Class A biosolids product. This presentation will discuss four key design considerations and lessons learned in laying out this facility: - Increasing reliability and availability of the Thermal Hydrolysis Plant (THP), - Design considerations for cake and sludge piping around the THP, - Challenges of an evolving market for combined head and Power (CHP) boilers on a THP project, - Squeezing the value out of biosolids. Consideration 1 Characteristics of the THP process make it potentially damaging to equipment. The inherent risks of piping and equipment failure create a need for periodic preventive and corrective maintenance shutdown for inspections and repairs, which will lead to annual periods of unavailability of the THP. Unavailability of the THP creates logistic issues with biosolids management and potential upsets downstream biological processes (digesters, sidestream), both of which the design must consider. Solution 1 A standard way to increase availability and reliability of a process is to provide this process with redundant units. When this option became available, WSSC chose to implement it through installation of add-on modules to the THP system and minor piping modifications. Consideration 2 Cake and sludge conveyance is energy intensive, and energy use is proportional to the length of the pipe. There are limits on pumps and pipe fittings that determine the maximum pressures a system can be designed for. In an ideal situation, cake reception (if using imported cake), storage, THP and digesters should be co-located, but when retrofitting an existing facility, this becomes a mighty challenge. Dual phase piping from the THP to the digesters requires a continuously ascending slope. Flow interruption on hydrolyzed sludge can create a big sticky mess. Solution 2 Most common methods to limit the headloss include use of long turning radius elbows, use of boundary layer injection (water or polymer), and other methods have been introduced in the market, such as air assisted cake pumping. When laying out a THP project, giving these elements the proper priority and importance can save big capital and operation costs. Consideration 3 Boilers in CHP systems for THP projects often have the ability to use engine generator exhaust gas and biogas along with other fuels (normally natural gas), for reliability and optimization of the energy use. They additionally need to be responsive to the steam demands which are inherently variable because THP is a semi-batch process. In Europe, composite boilers are the standard for THP projects, but the US market has not yet evolved to a point where these units are available. Instead, the standard approach for stream production from engines for CHP units is the use of heat recovery steam generators (HRSG). Bringing standard composite boilers to the US is not only extremely expensive, but also a total nightmare from the point of view of code compliance. The biogas boilers market in the US has mostly evolved from the landfill industry and there are limited options when it comes to using both engine exhaust gases and biogas. Solution 3 Available options in the US use co-firing of exhaust gas and biogas and provide limited windows of operation when it comes to limiting flame-out of the burners, due to the presence of the CO2 that comes along with the biogas. Innovative approaches using gas recirculation and multi-variable controls provide a feasible solution. Consideration 4 There are many paths to squeeze value out of the biosolids, which many times are focused on the use of THP to increase volatile solids destruction in the downstream anaerobic digestion, producing a higher value Class A biosolids, reducing hauling costs and increasing biogas production, but there are additional approaches to capture more value from THP process. Some examples of additional value include the use of biogas to generate power on engine generators, which can be coupled with a boiler than can use engine exhaust gases to improve the CHP unit overall efficiency. At Piscataway we set out to install CHP units that would serve the dual purpose of providing steam to the THP and electricity for the plant, as well as improving the energy independence from the grid. The WSSC bioenergy project is aimed at capturing the maximum value of the process without compromising the very real capital investment constraints. Solution 4 To achieve this optimization, we set out to design a CHP unit that would allow the project to apply for an energy grant offered by the State of Maryland, to CHP units that would achieve a minimum 60% energy efficiency. To reach this challenging goal, the CHP unit was designed in a way that not only included electrically efficient engines, and a boiler that uses the engine exhaust gases, but the overall system efficiency was supplemented with energy recovery from the engine secondary cooling system, through integration of this system with the Sidestream treatment process and pre-heating of the boiler feed water. Later in the project, a new more challenging energy efficiency goal was set, to achieve a 65% efficiency, to access additional grant funds from the local electrical utility company. Multiple options where analyzed, some of which were immediately discarded, some of which were later tossed out due to the complexity of their implementation and/or cost, and two were selected for implementation. The first one associated with additional energy recovery via additional preheating of the boiler feed water on economizers, and the second one, uses the heat from the engine cooling system to preheat the dilution water used to adjust the solids content in the THP feed.

ABSTRACT
City of Los Angeles Sanitation and Environment (LASAN) owns and maintains 10,800 kilometers (6,700 miles) of sewer and operates three Air Treatment Facilities (ATF) and ten Carbon Odor adsorbers located along the sewer system for removing odor and other related constituents from the collection system. The ATFs utilize Bio-trickling Filters (BTFs) technology followed by carbon adsorbers as polishing units while the Carbon scrubber sites utilize carbon adsorbers as the only treatment for foul air. In order to improve carbon life and reduce the footprint required for carbon vessels, LASAN started conducting a series of pilot tests to evaluate alternate carbon odor adsorbers with suspended media for all-around air flow compared with traditional flow carbon design. The results of this test were published in Water Environment Federation (WEF) Odor Conference in 2018 (Haddad-Zadegan/Gilani, WEF Odor Conference 2018 and UCLA Odor Conference 2017). The purpose of this test was to evaluate the performance of the new carbon vessel design with Suspended Media Chamber (SMC) and all-around air flow which provides larger media surface area, smaller footprint, and capability to separate moisture from the inlet air stream. This testing project conducted a side-by-side comparison between a deep bed traditional vertical upward air flow and the new all-around air flow design. LASAN procured and installed the new vessel design at eight (8) City carbon scrubber sites and this paper will share the result of the new scrubbers in term of their capability on removal of Hydrogen Sulfide (H2S) and other odorous compounds Volatile Organic Compounds (VOCs) from the inlet air stream. The new vessel design has the capability to separate the water voper from the inlet air stream contributing to a longer carbon life expectancy which results in significant cost savings for LASAN.

The Allegheny County Sanitary Authority (ALCOSAN) serves an area that spans approximately 310 square miles across 83 municipalities, including the City of Pittsburgh, Pennsylvania. ALCOSAN recently adopted a Clean Water Plan (CWP) to improve and protect the water quality of the region's streams and rivers by controlling combined sewer overflows (CSOs) and eliminating sanitary sewer overflows (SSOs). The CWP is part of a Federal Consent Decree (CD) to comply with the United States Environmental Protection Agency's CSO Control Policy. The CWP is made up of several components including preventing excess water from entering the sewer systems. As part of its green stormwater infrastructure (GSI) and source control (SC) program, ALCOSAN released Controlling the Source that lays out a consistent framework for evaluating GSI/SC in the Pittsburgh region. A key component involves identifying cost€effective and impactful GSI/SC projects capable of reducing sewer overflows to improve water quality. Overflow reduction efficiencies (OREs) were developed throughout the service area using automated modeling techniques to represent different GSI/SC techniques, varying implementation levels, and different system conditions. OREs provide a hydraulically-informed estimate of the relative overflow impacts of projects in different areas, so that effort and attention can be focused in those areas with the greatest potential overflow benefits. To complement the OREs, a GIS-based constraints analysis was performed to provide a geospatially-informed estimate of areas where GSI potential may be limited and/or costlier based on mapped physical and environmental constraints. Individual constraints such as shallow bedrock and slopes were assigned a range of constraint scores based the relative impact to GSI and then overlaid and summed. By targeting areas/sites with high OREs and lower levels of constraints, practitioners have powerful planning-level tools to identify projects most likely to be feasible, cost-effective, and impactful. Using these tools, ALCOSAN identified and evaluated almost 200 potential GSI opportunities. The opportunities were ranked and prioritized based on capture potential and implementation feasibility. Detailed concept plans for 60 of the higher ranked sites were developed and incorporated in discussions with municipalities as a tool to incentivize GSI project implementation in response to public comments received during the development of the CWP. This presentation will describe the development and application of the ORE modeling and the constraint scores as well as the results of the opportunity analysis and will discuss lessons learned for applicability in helping to address wet weather issues in other communities.

Anaerobic digestion is a process central to the stabilization of sewage sludges while also proven to be the effective first step in many resource recovery programs. Mesophilic anaerobic digestion has proven efficient, effective, and reliable process for decades. However, with increasing capital costs, increased value of recovered resources and a societal push toward decarbonization, in an attempt to limit the impacts of climate change; interest in intensification of the digestion process has grown. In the past decade the adoption of intensified or advanced digestion processes has increased. Processes like thermal hydrolysis, thermophilic digestion and co-digestion have demonstrated that conventional process limits, performance and stability indices need to be reassessed and defined for the next generation of water resource recovery facility. Metro Vancouver, has experience with advanced digestion technologies, like its Class A series thermophilic anaerobic digestion system at Annacis Island, pioneering its adoption in the late 1990's. However, since its adoption and nearly 20 years of effective operations the true capacity limits of this process have yet to be defined. To define the operational limits of a biological process, a range of process metrics must be considered these include: - Substrate loading capacity. -Minimum solids retention time - Acclimation potential to inhibitory compounds - Process reaction rates - Dynamic stress responses and recovery (load, temperature, feed composition, toxicity, etc.) To elucidate these metrics at scale is possible, but the impacts of potential process failure can be significant, including long recovery times, process restart, loss of treatment and odors. Any of which can represent significant costs when managing thousands of cubic meters of material (millions of gallons). These risks further increase when new processes are being implemented and/or augmenting an existing digestion process. Further, testing new unproven technologies at scale that on paper would appear to be effective often prove to be more complicated than first envisioned, resulting in increased costs. These costs could result in a premature cessation of process development. One approach researchers and early adopters have addressed these challenges is through the bench testing, on-site and at universities. While these often provide evidence for proof of concept, they are limiting in scale and scope; often not integrating the true variability in operation that a full-scale facility, leading to conservative designs or non-adoption due to risk avoidance. Ultimately this slows the progression of technology advancement. Metro Vancouver, has elected to accelerate the testing and adoption of new processes for its wastewater treatment plants through the construction of the Pilot Digestion Facility (PDOF). This facility consists of three 8 cubic meter digesters, and a feed skid. The digesters are capable of operating at range of temperatures, retention times, mixing strategy and process phasing strategies. The PDOF not only allows for new processes to be tested but also existing systems to be stress tested to defined the maximum capacity of their existing assets. Further, at this scale, it is possible to test processes under real-world conditions, to better assess implementation at scale and process viability at scale. In June of 2023, the PDOF completed construction and commissioning and was started-up at the Lulu Island Wastewater Treatment Plant, in Richmond, BC. One of the first test plans implemented was to evaluate the reproducibility of pilot results relieve to the full-scale operating digesters. Three PDOF digesters were operated at solids retention times of 15, 20 and 28 days respectively on a mix of thickened primary (TPS) and waste secondary sludge (TWSS). Core process metrics were monitored to determine, system performance and compared to the full-scale operating digesters. Figure 1, shows the relationship between digester operating SRT and volatile solids destruction, after each of the three test digesters had reached stead-state and compared it to reference data and LIWWTP's current digester operations. What is apparent from the PDOF and the reference data is that 15 days SRT appears to be an inflection point around which further reduction in operating residence time will result in notable reduction in solids destruction which ties directly to biogas production. The current industry primary practice for resource recovery is biogas generation and methane utilization. Understanding this inflection point and being able to accurately test around this point will provide significant understanding of the total benefit of future process optimizations. Further what is also apparent is that the sludge a LIWWTP is more degradable than a 'typical' sludge, based on the reference data information. This is likely due to a combination of very low industrial input, high volatile content and a low overall residence time in the secondary system, a trickling filter solid contact system. The fact that the PDOF system produced similar VSr to the full-scale, suggests the system is performing in a similar manner to the full-scale digester, making extrapolations to full-scale relatively direct. In terms of reproducing the performance of the anaerobic digesters at LIWWTP, there was generally good agreement in the data, between the pilot and the full-scale digesters in terms of solids destruction, volatile acids, alkalinity and ammonia, Table 1. Biogas data was not completely reliable during this time as condensate was impacting meter accuracy on the pilot units. Modifications to the meter orientation, appears to have improved the response. As part of understanding the overall potential of anaerobic digestion and to gather further in-sites as to the fundamental mechanisms driving the observed results, microbial ecology analysis was conducted to understand changes in the consortia present. As part of this baselining observation the result of these efforts will be discussed. Figure 2, presents the relative abundance of different phylum level populations with time for each of the PDOF digesters and a single steady-state point for the LIWWTP digesters. Figure 3, further refines that focusing Euryarchaeota, which contain the methanogens. With the successful demonstration of the mesophilic operation of the PDOF facility, completing commissioning, the first tests of intensified digestion have commenced. The process being converted over to thermophilic operations to evaluate the limitations of the process. As of authoring the digester temperature has been increased and the microbial population is transitioning to thermophilic, as denoted by the significant increase in volatile acids and deterioration of biogas production. A process condition understood to be typical. Once steady thermophilic operation has been reached a range of process conditions will be tested. These include, reduced SRT and increased organic loading rate. This not only will demonstrate the potential for LIWWTP to utilize thermophilic digestion to increase capacity but also further define the capacity at the larger Annacis Island WWTP. This paper will discuss the results of the completed baselining operations, including lessons learned, and observation due to different operating retention times for mesophilic digestion. It will further present relevant observations from the conversion to thermophilic, which are in progress now.

1. Introduction Since 2019, 4.1M wet tons of sludge cake were produced annually at WRRFs in South Korea. Following the elimination of ocean dumping as a disposal strategy in 2006, sludge management costs have climbed significantly. As of 2018, sludge disposal reached an average of $120 USD/wet ton (MOE & KECO, 2021). In 2019, only 67 out of 4,216 Korean WRRFs larger than 500 m3/d (132,000 gpd) included anaerobic digesters (MOE, 2020). Since digestor projects cannot be deployed quickly or cheaply enough to keep up with rising disposal costs, alternative sludge reduction processes are being sought by public agencies. The thermal hydrolysis process (THP), traditionally applied as a pre-treatment for anaerobic digestion, can also be applied as a sludge cake minimization strategy in the absence of digestors. This paper describes recent pilot and full-scale demonstrations of this concept, including identification of new optimal operating setpoints specific to this application, as well as downstream dewatering performance and economic impacts. 2. Materials and Methods 2.1 Thermal Hydrolysis Process This paper describes a new thermal hydrolysis process (THP) developed and commercialized by BKT/Tomorrow Water. The process, trade-named Draco, is a three-stage, batch process comprised of a pre-heating tank followed by reactor and decompression tanks. Steam is used to build heat and pressure in the reactor vessel, causing cell lysis and improving the dewaterability of cellular sludges. The Draco process is differentiated by the inclusion of a paddle mixer in the pre-heating and reactor tanks, novel steam sparger configuration, and the use of novel temperature setpoints (as described below). 2.2 Pilot testing A containerized Draco THP pilot was deployed to a municipal WRRF in Dangjin (Korea) to process 2 wet tons/d of undigested biological sludge cake from August to October, 2021 (Figure 1). The pilot was fed mixed primary and waste activated sludge (WAS) which had been dewatered to 20.0±1.2% dry solids (DS) and fed without dilution into the Draco process. To optimize the temperature setpoint for hydrolysis of undigested sludges, influent dewatered cake was processed at either 170, 180, 190 or 200oC for 30 min. Capillary Suction Time (CST) was measured following THP as a measure of dewaterability in thermally processed sludges. To assist in optimization and selection of dewatering equipment, the 190oC-processed sludge product from the Draco THP pilot was fed into either a plate-and-frame filter press (operated at 15 bar) or a belt filter press (operated at 15, 30 and 50 bar.) The plate-and-frame filter press was operated without any chemical addition, while the belt filter press was operated with addition of cationic polyacrylamide polymer at 0.64%/kg dry solids. 2.2 Full scale operation A full-scale Draco THP system combined with a plate-and-frame filter press was installed at a slaughterhouse wastewater treatment plant in Gimhae, S. Korea. This integrated sludge minimization system, operating since June of 2019, processes roughly 50 wet tons/d of dewatered WAS containing 14.8±0.5% DS. Upstream, the slaughterhouse's wastewater is treated by a sequencing batch reactor (SBR), and sludge wasted from this SBR has similar characteristics to undigested municipal WAS. Sludge was fed undiluted into the Draco THP and processed over more than 2 years. 3. Results 3.1 Pilot Results Over three months of pilot testing, normalized capillary suction time (NCST) decreased as the processing temperature increased, while specific capillary suction time (SCST) increased with temperature (Figure 2). This suggests that higher THP temperatures produce better downstream dewatering performance. At the same time, the marginal improvements in dewatering indicators (NCST, SCST) between 190oC and 200oC were relatively minor, while the added steam energy required to meet the higher setpoint was significant. As such, 190oC was selected as the optimal temperature setpoint for this application. In subsequent dewatering testing with hydrolyzed pilot sludge, dewatered cake from the plate-and-frame filter press averaged 52.8% DS, while cakes from the belt filter press ranged from 37-41% DS, dependent on belt pressure (Table 1). Based on the higher dewatering performance and lack of chemical inputs required for the plate-and-frame press, this equipment was selected for an upcoming full-scale installation over the belt filter press. Table 2 lists the average filtrate quality of the plate-and-frame press in the pilot, which needs to be sent back to the head of the wastewater plant for treatment in full-scale installations. 3.2 Full-scale results Over 27 months of operation, the full-scale Draco process increased the dry solids content of dewatered WAS from 14.8±0.5% to 53%±1.1%. The intermediate-stage solids content of the thermally hydrolyzed sludge was 11.8±0.7% at the output of the decompression tank, and was subsequently dewatered in the press to over 50% solids. Dewatered cake following the Draco process was compact and easily handled (Figure 3). By installing a THP plus filter press, this plant reduced its overall sludge cake output to disposal by 80% (by volume). This translated into a 67.6% reduction in sludge disposal costs, even after energy costs of the THP process were factored in (Table 3). 4. Discussion and Conclusions This paper describes the optimization and application of a combined THP and dewatering process intended for use at WRRFs which do not anaerobically digest their sludge. Pilot testing demonstrated that dewaterability of municipal THP sludge increases with increasing THP temperatures from 170oC up to 190oC. At higher temperatures of 190-200oC, the marginal benefit in dewaterability was outweighed by the marginal cost in energy requirements. The combination of Draco THP at 190oC, coupled with a plate-and-frame dewatering press, was able to consistently achieve sludge cake dryness over 50% in both pilot and full-scale installations. Sludge cakes above 50% DS are much easier to process in thermal sludge dryers, due to the avoidance of a plastic 'sticky phase' occurring between DS 35-50% (Peeters, B., 2010). As this study demonstrates, plants which utilize sludge dryers can benefit significantly from the addition of a THP, since THP allows dryers to be fed a much lower-moisture cake (up to 30% less moisture), reducing the amount of energy required in thermal drying and dramatically reducing the size of dryer required. Compared to the energy required to dry a typical dewatered cake from 20% to 90% DS, drying post-THP cake (at >50% DS) to the same moisture content saves about 40% in total energy inputs, even after factoring in the energy required for hydrolysis and dewatering. These results suggest that Draco THP, paired with the right dewatering press, can serve as a cost-effective strategy for reducing sludge volumes and disposal challenges, even for WRRFs without anaerobic digestors. At the Gimhae plant, application of this process reduced sludge volumes by 80% and cut disposal costs by 68%, achieving a simple payback of 4-6 years.

Charlotte Water (CLTWater) has 123 MGD of capacity between five major wastewater treatment plants (WWTPs) and is interested in sustainable and cost-effective technologies that may be selected for future WWTP expansions or for replacement of existing treatment infrastructure. Aerobic granular sludge (AGS) is an innovative secondary wastewater treatment technology that can achieve biological nutrient removal (BNR). Aqua-Aerobic Systems, Inc (AASI) is the vendor for AquaNereda, the patented AGS system that utilizes specific biological and hydraulic selection pressures to produce and maintain the AGS in a sequencing batch reactor (SBR). CLTWater elected to pilot AquaNereda to understand how it might be used to expand the capacity of our overall system, either at an existing plant or in place of another BNR technology at our new plant under design, the Stowe Regional Water Resource Recovery Facility (SRWRRF). An AGS pilot was performed at McDowell Creek WWTP from June 2019 to February 2020 to determine its viability as a treatment for CLTWater. Before starting the AquaNereda pilot, CLTWater developed a list of objectives to achieve during the piloting process with actionable and achievable goals defined for each objective. These objectives included 1. Evaluating simulated performance representing treatment with and without primary clarifiers 2. Observing development of granules from flocculant sludge 3. Evaluating solids characteristics 4. Evaluating process control and operability 5.Involving State regulatory agencies to facilitate potential future permitting processes To address the objective of evaluating solids characteristics, a separate solids study was conducted at Bucknell University to provide insight on solids handling and treatment impacts for potential full-scale Nereda implantation. CLTWater wanted to assess impacts to digestion performance, dewatering, and recycle streams when aerobic granular sludge (AGS) and conventional activated sludge (CAS) are treated concurrently. During the study, Bucknell operated four lab-scale digesters that were fed several solids blends (Table 1) including two 100% thickened waste activated sludge (WAS) digesters to demonstrate differences between AGS and CAS WAS and two 60% primary sludge (PS)/40% WAS digesters to simulate McDowell's current digestion process and the expected maximum contribution of AGS to any digestion process at CLTWater. Waste solids from the Nereda pilot reactor treating primary effluent were thickened to ‰¥5% using gravity belt thickening and shipped to Bucknell with thickened PS and CAS-WAS from McDowell's full scale processes. Bench-scale 20-day HRT mesophilic anaerobic digesters were fed daily. Biogas production was monitored throughout the trial, but other analyses were performed after 71 days (~3.5 SRTs) to ensure results were representative of steady-state conditions. Results include quantified metrics and other observations related to 1) digester performance VS destruction, biogas production; 2) solids handling sludge viscosity, polymer demand, cake solids, cake metals content and odor production; and 3) recycle streams digestate nutrient concentrations. For digester performance, results showed that volatile solids reduction (VSR) for AGS-WAS was comparable to CAS-WAS with slightly different methane yields between Digesters 3 and 4 (60% PS/40% WAS). Minor differences in solids handling parameters were observed including marginally higher viscosity and polymer demand for digested solids that included AGS, but these differences were more pronounced in the digestate from Digesters 1 and 2 (100% WAS). Recycle stream soluble TKN concentrations were similar regardless of WAS source; however, recycle streams from reactors including AGS-WAS were characterized by markedly lower soluble TP concentration. The finding of much lower soluble TP concentration for AGS-WAS was surprising given that the Nereda process includes enhanced biological phosphorus removal (EBPR) and the pilot reactor performed comparable EBPR as the full-scale mainstream conventional BNR process. Unfortunately, the pilot timeline did not allow for additional investigation into the cause of this observation, but further research may be warranted in this area. This presentation will discuss high-level results from each of the objectives targeted during the AquaNereda pilot but will focus mainly on the solids-related findings. We will present overall conclusions from the pilot as well as lessons learned related to implementing a pilot for a process that has broad reaching implications across a wastewater treatment plant. Finally, the future of AGS implementation at CLTWater will be discussed.

SUMMARY The cost and complexity of projects implementing thermal hydrolysis pretreatment (THP) at municipal water resource recovery facilities (WRRFs) has led many utilities to utilize alternative delivery approaches. Raleigh Water selected Construction Manager At Risk (CMAR) to deliver its Bioenergy Recovery Project at the Neuse River Resource Recover Facility (NRRRF). WSSC Water utilized Progressive Design Build (PDB) to deliver the Bio-Energy Project at the Piscataway WRRF. The benefits of THP-enhanced digestion are many, from increased volatile solids reduction and biogas production to higher digester loading and therefore less required digestion volume. Some of the considerations involved with implementing THP include sludge preconditioning and treatment of high-strength post-digestion recycle streams. The cost and constructability feedback made possible with alternative delivery helped the design teams for the Raleigh Water and WSSC Water projects identify the optimal solution for each project, with a collaborative approach to the site-specific benefits and challenges associated with THP implementation. This 'case study' provides a summary of these two projects from design, through construction, and commissioning. It will focus on the unique aspects of each project, highlighting the role that alternative delivery played in influencing the design and start-up of these projects. BACKGROUND & Raleigh Water's Bioenergy Recovery Project Raleigh Water is implementing a Bioenergy Recovery Project to produce green energy and a Class A biosolids product, demonstrating the City of Raleigh's commitment to sustainable local government operations. By transitioning to THP and anaerobic digestion, Raleigh Water can convert the methane generated in the process to renewable natural gas (RNG) to fuel the City's bus fleet. Using RNG for vehicle fuel will offset greenhouse gas (GHG) emissions, supporting the City's aggressive community-wide goal of an 80-percent reduction in GHG emissions by 2050. The Bioenergy Recovery Project will be net energy producing, qualifying Raleigh Water for a $50M zero percent interest loan under the Clean Water State Revolving Fund (CWSRF) Green Project Reserve. The project was recognized nationally as Exceptional under CWSRF's Performance and Innovation in the SRF Creating Environmental Success (PISCES) program. Raleigh Water manages residuals from all three of its wastewater treatment plants at the Neuse River Resource Recovery Facility (NRRRF), the largest permitted treatment works in North Carolina with a rated capacity of 75 mgd. Current biosolids management includes lime stabilization, aerobic digestion, and off-site composting. As the existing solids handling equipment neared the end of its useful life, the utility was motivated to explore alternative biosolids management strategies, specifically those that maximize the potential for resource recovery and minimize GHG production. The Bioenergy Recovery Project will use THP to maximize the efficiency of new anaerobic digesters, achieving a nearly 50-percent reduction in mass and generating enough RNG to fuel 50 City buses. €ƒ BACKGROUND & WSSC Water's Bio-Energy Project The WSSC Bio-Energy project centralizes biosolids processing from WSSC Water's five WRRFs at the 30 mgd Piscataway WRRF to produce a Class A biosolids product. In addition to the THP and anaerobic digestion processes, the overall project also includes cake receiving, solids screening, pre-dewatering, cake pumping, pre-THP cake storage, post-dewatering, cake conveyance, Class A cake storage, sidestream nitrogen removal, odor control, renewable natural gas production, gas storage, combined heat and power generation and steam boilers. The Bio-Energy project will fundamentally change how WSSC produces biosolids, allowing a focus on long-term sustainable end products with a Class A dewatered cake biosolids and renewable natural gas suitable for pipeline injection and vehicle fuel. The project will overall reduce the greenhouse gas emissions from WSSC by 15% and result in nearly $3 million per year in operation cost savings. COLLABORATIVE DELIVERY DURING DESIGN Some of the biggest benefits of alternative delivery include quick cost and constructability feedback during design. After the CMAR came onboard the Raleigh Water Bioenergy Recovery Project, cost estimates were provided at the 60-percent design level to inform value engineering for the project. Cost feedback continued throughout design, which progressed to 100-percent completion level for Guaranteed Maximum Price (GMP) development. At the beginning of the detailed design process of WSSC Water Bio-Energy Project, the PDB team considered how best to approach a series of critical decisions related to the digestion process to provide the best long-term solution for process performance, energy efficiency, and accommodation of potentially high volume expansion considerations while balancing capital costs. The critical decision areas that needed review and discussion included: digester construction method; digester mixing approach; digester volume/dimensions; rapid volume expansion containment approach; and digested sludge storage approach. These five decision areas were considered individually and collectively to understand the range of advantages and disadvantages that each would have on the overall project. SUCCESSFUL COMMISIONING Commissioning new equipment and processes can be challenging, especially when facilities must maintain operations and compliance with treatment standards. Discussions began during design to identify the optimal start-up and commissioning approach for each project. The different alternative delivery methods employed led to different roles, responsibilities, and contractual requirements for each project. This paper will review the start-up and commissioning plan for both projects.

King County's Wastewater Treatment Division (KC-WTD) standardized its dry media scrubber systems to utilize the horizontal airflow vertical bed (HAVB) configuration (Figure 1). This was done due to the relative ease the HAVB configuration provides for media removal and replacement relative to the traditional deep bed configurations and other designs. With almost thirty HAVB scrubbers in service and more than 18 years of experience with this configuration King County staff have refined their standard design based on lessons learned about scrubber vessel geometry, media bed retention system design, drainage, and maintenance access. KC-WTD staff have recently received reports from others in the wastewater industry that some utilities are still having difficulties with the operation of the HAVB configuration. The aforementioned lessons, design details and insights will be shared in this paper in the hope that others may benefit from KC-WTD's experience and avoid such difficulties. The HVAB circular cross section configuration allows spent media to be removed easily with a vacuum truck (Figure 2) and replaced easily by dropping replacement media in via large access hatches (Figure 3). However, if the media fill ports are not appropriately dimensioned with respect to the vessel diameter, gaps may form between the media and the vessel wall which will allow foul air to bypass the media and escape treatment which can lead to odor impacts. KC-WTD staff have developed, and will share in this paper, a simple means of avoiding the problem by comparing the fill port dimensions, vessel diameter media's angle of repose (Figures 4 and 5). KC-WTD has also encountered problems with media bed retention system failures, accessing the scrubber interior to perform routine maintenance and repair of internal scrubber features, drainage of condensate, media sampling port design and other issues that have caused difficulties both in the operation and maintenance of HAVB dry media scrubbers. The lessons learned from these problems have allowed the refinement of KC-WTD's HAVB design standard that operate successfully. It is hoped that by sharing these lessons and solutions that were developed will help others who choose to incorporate the HAVB dry media scrubber configuration into their odor control systems.

Since 1998, Seattle Public Utilities (SPU) has innovated with retrofits of public right-of-way to improve stormwater using natural drainage systems (NDS). Based on lessons learned from prior projects and to address regulatory commitments, SPU launched the NDS Partnering program in 2017 to develop retrofits in the three major creek watersheds within the City: Longfellow Creek, Thornton Creek and Piper's Creek, see Figure 1. Due to topography, historical development patterns and standards and economic considerations much of this part of the city consists of informally developed right-of-way without curb or formal drainage infrastructure. This presentation will share the program goals, a summary of the site selection process and more importantly lessons learned in addressing the challenges and opportunities of partnering to retrofit underdeveloped urban right-of-way. The Plan to Protect Seattle's Waterways is a comprehensive strategy that embodies SPU's commitments that were documented in the July 2013 Consent Decree to address combined sewer overflows. It meets Seattle's federal commitments to create a Long-Term Control Plan (LTCP) that will make water quality improvements to Seattle's receiving waters, e.g., Puget Sound, Lake Washington, and the urban creeks that feed them. The final Plan received final approval in August 2015. Within the Plan to Protect Seattle's Waterways, SPU recommended the Integrated Plan (IP) alternative, which addresses water pollution from both combined sewer overflows and stormwater-only runoff into waterways. As part of the IP, SPU is committed to deliver high-value stormwater-only projects/programs ahead of a set of smaller-volume combined sewer overflow (CSO) projects for a greater overall water quality benefit. NDS Partnering is one of the three stormwater-only projects/programs recommended in the IP for pollutant reductions. In addition, the NDS Partnering program fits within SPU's Strategic Business Plan Focus Area No. 1, 'Better Protecting Your Health and Environment.' The mission of the NDS Partnering Program is to achieve the water quality goals identified in the City's Plan to Protect Seattle's Waterways. The NDS Partnering program emphasizes working with sister agencies, concurrent SPU programs and community partners to deliver high-value neighborhood improvements, including bioretention systems that will capture and treat stormwater before it drains to creeks feeding Puget Sound and Lake Washington. The purpose of the partnering in the NDS program is to develop shared projects within Seattle Public Utilities (SPU) programs and between SPU and other City agencies, such as Seattle Department of Transportation (SDOT), to offer multiple benefits to neighborhoods and ecosystems, including: greener, more attractive neighborhoods, lower risk of flooding, additional natural habitat for native plants and animal species, healthier creek ecosystems, calmer traffic patterns, and more street trees. For SPU, the NDS projects provide water quality treatment for street runoff that drains to urban creeks by retrofitting the roadsides with NDS (also referred to as bioretention cells) and addressing localized flooding issues. The City of Seattle has a long history in developing retrofits of right-of-way in urban creek basins beginning with the SEA Streets project in 1998. This presentation will focus on the current NDS program consisting of the Longfellow Creek Basin (due to be complete with construction in 2023), South Thornton Basin (due to begin construction in Spring 2023) and North Thornton and Pipers Creek Basins (under development and design). This program leverages innovations developed under some of the most recently constructed retrofit projects including the Delridge, Ballard (Phases 1 and 2) and Venema NDS projects to enhance the viability of green infrastructure in challenging site constraints and soils. These innovations include the use of weirs, underdrains, structural soil cells and underground injection control (UIC) wells. Working in underdeveloped or informally-drained right-of-way presents opportunities to address infrastructure gaps that will benefit the local community, specifically providing traffic calming, improving pedestrian access, and correcting nuisance drainage. This presentation will share the approach and response to community outreach to communicate impacts and receive feedback on tradeoffs on design of improvements. Additionally, the co-location of improvements with partner agencies presents opportunities to reduce overall project cost for the City balanced with increased coordination needs. Key issues addressed by the project include how to negotiate space constraints to co-locate new sidewalks with bioretention facilities in existing right-of-way. Another key issue commonly expressed by the community is minimizing impacts to automobile access and parking where historical use is informal and haphazard and existing driveways do not conform to code. Public investment in infrastructure presents the opportunity to improve community spaces and services. In addition to considering equity and deep connection with the community through the design process, the program also has had opportunities to incorporate art and create community spaces. This presentation will include examples where the projects have included a range of scale of art from small touches to enhance the individual elements of the green infrastructure to more significant efforts to incorporate public art in new pocket community spaces that are co-located and funded with the NDS projects. The project also specifically targets addressing local drainage issues where informal drainage is inadequate to collect and convey runoff from the neighborhood streets creating nuisance flooding. While addressing these local drainage issues is a significant benefit for the neighboring property owners, SPU was also challenged to incorporate NDS and drainage improvements in a manner to avoid conveying the additional runoff to create or aggravate existing issues downstream. The program addressed these challenges by evaluating the downstream system capacity, maximizing stormwater retention within the project and providing compensatory storage where required to minimized downstream impacts. In summary, this presentation will provide the opportunity to share lessons learned at a unique point in time that represents past, present and future of a program that is delivering green infrastructure improvements to over 60 blocks of neighborhood streets in the City of Seattle's urban creek watersheds. This program and presentation deliver unique and innovative techniques to balance the needs of the right-of-way to improve the quality of stormwater runoff. SPU strives for continual program improvement and delivering community-centered projects that achieve improved service with reduced costs.

Faced with increasing costs for controlling hydrogen sulfide in its wastewater collection system, the City of Bakersfield, California commissioned an evaluation of its odor control program in 2019. Among the consultant recommendations was to consider using a more efficient treatment (ferrous chloride) in place of certain of the existing Calcium Nitrate dosing stations where costs were constrained. A particular priority were those stations along the higher flow interceptor segment where chemical demands and community sensitivities were highest. An expected benefit of iron dosing is its durational control capability, which should translate into fewer dosing stations. Consequently, field testing was suggested to assess the cost-benefit. As siting dosing stations for ferrous chloride solutions can be limited (due to the corrosivity of the product), a low-hazard form of ferrous chloride, SulFeLox®, was used. The study was conducted from April to June, 2021, and consisted of 12 days monitoring of the baseline Calcium Nitrate scenario, followed by 60 days of SulFeLox dosing at different feed rates, and concluding with 14 days of no chemical dosing (i.e., the true baseline scenario). The interceptor selected for the test was a 10-mile (5-6 hour retention), 12 mgd trunkline leading to the City's Plant No. 3 (Figure 1). The particular segment of focus begins where the discharge from the Romero PS (S1) enters the interceptor and ends at the Buena Vista PS (S2) approximately 3 miles (2 hours) downstream. Controlling vapor-H2S levels at the Buena Vista PS was the primary measure of success. To assess the durational control aspects of each chemical, sampling was also performed another 3-4 miles downstream at the McCutcheon PS (S3) - just ahead of the treatment plant (S4). In this study, the SulFeLox dosing station replaced two Calcium Nitrate stations: 1) at the Romero site (S1), and 2) at the Buena Vista site (S2). With Calcium Nitrate dosing (310 gpd, combined, from the two sites), the peak vapor-H2S levels recorded at the four sampling sites averaged 3, 94, 595, and 100 ppm (Figure 2a). The liquid-phase sulfide levels were 0.0, 2.9, 6.6, and 3.5 mg/L, respectively. With SulFeLox dosing (120-210 gpd), the peak vapor-H2S levels recorded at the four sampling sites averaged 0, 30, 652, and 31 ppm (Figure 2b). The liquid-phase sulfide levels were 0.0, 1.4, 4.7, and 2.3 mg/L, respectively. Comparing the Calcium Nitrate and SulFeLox results shows 66-83% lower vapor-H2S peaks at the Buena Vista (S2) and treatment plant (S4) sites, with less benefit at the McCutcheon site (S3) where vapors are impacted by H2S by other flows into the station. (Figure 2c). Site 2 (Buena Vista PS) is located in a particularly sensitive area, and prior tests suggested upstream Calcium Nitrate feed rates would need to be 500 gpd (or more) to maintain vapor-H2S levels below 25 ppm. Figure 3 shows the vapor-H2S results in this test, where SulFeLox feed rates of 120-210 gpd achieved the compliance targets and provided H2S reductions of 84-95% (relative to 146 gpd Calcium Nitrate). On a performance basis, the field results confirmed the consultant recommendation that (for system-wide H2S control) iron dosing from one site could provide improved results relative to Calcium Nitrate dosing from two sites. SulFeLox feed rates were determined that provide interceptor-wide H2S control to 25 ppm and 10 ppm. However, a direct cost comparison between the two treatment chemistries is complicated given that system-wide H2S control could not be demonstrated with Calcium Nitrate (per the 500 gpd test in a prior study). This present study did show, however, that the cost to control to target H2S levels using SulFeLox was $600-1000 per day, where the recurring cost for Calcium Nitrate was $850-950 per day (to control to the higher level of 100-140 ppm H2S). Subsequent to this field test, the City continued to feed SulFeLox at S1 (Romero PS) and has since replaced seven other Calcium Nitrate sites with three SulFeLox sites, reducing the total number of chemical feed sites from nine to four. As a result of this work, the City is now spending approximately $660 k/yr for SulFeLox to meet its system-wide performance targets, where it was previously spending $990 k/yr (for Calcium Nitrate). Further, with now a year's experience with dosing iron into the collection system, the treatment plant has observed operational benefits, including the elimination of need for ferric chloride feed to the plant digesters. Early in 2022, the City entered into a five-year supply agreement for providing SulFeLox iron product and related services and equipment. Future work is planned to evaluate iron regeneration ahead of the treatment plant (at McCutcheon PS, S3), recognizing that this trunkline comprises 70% of total plant flow but 100% of influent iron. Oxidizing the spent iron (as FeS) to hydrous ferric oxide (using hydrogen peroxide) is expected to provide additional benefit to treatment plant operations. Figures 1. Schematic of interceptor segment tested 2. Summary of field test results: Calcium Nitrate and SulFeLox rate performance 3. Buena Vista PS: Response of vapor-H2S levels to chemical feed rates (at the upstream Romero PS). 4. Buena Vista PS: Dose-Response summary comparison of SulFeLox to Calcium Nitrate.

Speakers: Karen Counes Program and Construction Management Practice Leader CDM SMITH Jenn Harrison Regional Team Leader, Program and Construction Management CDM SMITH Julie Lucas Senior Manager of Talent Acquisition Programs CDM SMITH Sara Varvarigos, Transportation Planner and Reboot/Re-entry Graduate CDM SMITH Category: Diversity & Inclusion - Presentation title: Reboot Re-entry: Returning to a Technical Profession After a Career Detour - Description: Two steps forward, two steps back. Sometimes detours happen in our well-planned lives. If you have had a break in your science, technology, engineering, and mathematics (STEM) career and are now ready to get back in the game, let CDM Smith help you restart your career by participating in our career re-entry program. In partnership with the Society of Women Engineers and iRelaunch, we offer a 16-week program each January through April for those who left their STEM career for 2+ years and now want to return. This is a paid, full-time temporary opportunity to help you train and rejoin peers in your field. Abstract/Content In 2018, CDM Smith joined a task force with the Society of Women Engineers (SWE) and iRelaunch, a pioneering organization on career return-to-workspace and essentially 'returnships' intended to re-integrate technical professionals into the workplace after career detours. SWE's STEM Reentry Task Force and iRelaunch's research and training programs were the basis for CDM Smith's Reboot/Re-entry Program, a 16-week, 40 hrs/week paid 'returnship' geared toward those employees trained in technical professions such as engineering and construction, but had taken a hiatus in their professional career. CDM Smith's formal Reboot/Re-entry program began in 2019, and can now claim 6 full-time hires as a result of the program.