Conference Papers

Purpose of the Presentation
The purpose of the presentation is to demonstrate the innovative approach to assessing sanitary sewer overflow compliance being used by Christchurch City Council (CCC), New Zealand. Continuous simulation of long-term rainfall data is used by CCC to assess overflow compliance rather than using a synthetic rainfall pattern that is intended to represent the target return period. Furthermore, collection system planning is based on a design storm that was generated based on statistical analysis of the 25-year rainfall continuous model simulation results. The presentation will show that SSO frequencies are sometimes not well represented by rainfall events that have an equivalent return period and that antecedent rainfall conditions and hydrologic and hydraulic (H&H) routing of flows unique to each collection system can help to select a better design storm to simulate overflow return periods of interest.

Benefits of the Presentation
This presentation should be selected because it will provide the following benefits to the audience and industry:
-- it will illustrate the difference in overflows predicted using a synthetic return period rainfall event and the overflow frequencies calculated based on continuous simulation of long-term rainfall.
-- it will show how the environmental regulators for Christchurch, New Zealand require continuous simulation of long-term rainfall to validate overflow compliance.
-- it will demonstrate the value in reviewing continuous simulation overflow results to develop more accurate design storms to be used for infrastructure planning.
-- it will show how a utility can use an improved approach to developing design storms to ensure investments are made in new infrastructure and infrastructure rehabilitation programs that are targeted in the relevant area of the collection system in order to meet consent conditions effectively.
-- it will illustrate how three different 15-year windows of rainfall from a 25-year period of rainfall can affect the outcome of the overflow frequency assessment but that the climatic variations do not have a significant bearing on the outcome of the overflow compliance.

Project Background
Christchurch City Council provides drinking water, stormwater, and wastewater across five council areas in the North Island, New Zealand. Christchurch has a complex wastewater network serving 373,000 people. Christchurch has a large and complex wastewater network serving approximately 373,000 people with a single wastewater treatment plant capable of treating 650 megaliters/day (MLD). Christchurch has two main river systems: the Avon River and the Heathcote River, which both flow into the Avon-Heathcote Estuary which then flows into the Pacific Ocean (see Figure 1). Christchurch City Council (CCC) holds a resource consent (permit) for the overflows to waterways. The resource consent allows an overflow frequency to each of these receiving environments which decreases over time to a 2 year ARI, based on 15 years of long time series modelling. In addition, no overflow site may overflow more than every six months on average, based on the same long time series modelling. The Christchurch Overflow Compliance Assessment project was commenced and completed in 2020. The project was completed using the latest model calibration completed in 2020 and was an update to the overflow compliance assessment completed based on the model previously calibrated in 2015. The overflow consent conditions require that continuous simulation of the most recent 15-years of rainfall be completed to assess the system performance. This project included continuous simulation of the most recent 25-years of rainfall and analysis of overflow results from three different 15-year windows to investigate whether the overflow frequencies are significantly affected by the 15-year window of rainfall selected. Overflow control measure alternatives to achieve the 2-year overflow return period target were previously assessed using a synthetic rainfall pattern. To determine whether this rainfall pattern would be appropriate for future planning studies, the long-term continuous simulation results were used to predict the location of overflows occurring more frequently than once every two years and then compared to the locations predicted using the synthetic rainfall pattern. This assessment demonstrated that the synthetic event did not provide a good representation of actual overflows and a new design storm was developed based on historic events.

Project Details
The objective of the wet weather overflow compliance assessment was to determine wastewater overflow compliance with the consent conditions stipulated by the environmental protection agency, Environment Canterbury (ECAN). This was undertaken using the calibrated hydraulic model to simulate system performance based on continuous rainfall data from the period of 1995 to 2020. To determine whether the rainfall window could have an impact on any of the consent compliance results, the assessment of overflow frequency and volume was performed for the following time periods:
1. 1995 to 2020
2. 1995 to 2010
3. 2000 to 2015
4. 2005 to 2020

The compliance assessment results summarised in Table 1 and Table 2 below, show the level of variation in overflow response according to the rainfall window chosen. While the variations are significant in some time windows, the compliance outcomes would not have been affected. Table 1: Overflow volume in each catchment for different time periods Table 2: Overflow frequency in each catchment for different time periods The objective of the design storm review was to ensure the design storm used for wastewater infrastructure planning is representative of a 2-year return period based on the 25-year continuous simulation results. The assessment was based on overflow volume, peak and spatial distribution. The 25-year continuous simulation results were reviewed to identify historical events that corresponded to an overflow return period of approximately 2 years. Due to a high degree of rainfall spatial variance in the historical events that were close to a 2-year return period, it was decided to repeat the overflow statistical analysis by receiving environment rather than system-wide. Based on the results from the overflow statistical analysis, several 2-year design storm alternatives (synthetic and historical) were shortlisted. The preferred 2-year design storm, presented in Figure 1, was the August 5, 1995 (northern basins) and April 17, 2014 (southern basins) composite event. This event provided the best representation of 2-year ARI overflow volumes, peaks and spatial distribution and comprised events of sufficiently short duration to be convenient for planning.

Conclusion
The results from this study demonstrate a novel and improved approach to developing design storms to ensure investments are made in new infrastructure and infrastructure rehabilitation programs that are targeted in the relevant area of the collection system in order to meet design criteria and/or compliance targets.

A sluggish velocity in critical decisions by utility Boards, Councils, and Commissions presents a significant risk to addressing the complex challenges in the modern water/wastewater utility. Including real-time data storytelling as part of a comprehensive business intelligence program can significantly accelerate decision velocity. When coupled with a utility-wide modern data warehouse that feeds the business intelligence platform all of the utility's disparate data in real-time, full decision perspective can be continually delivered to the decision maker no matter how complex the decision nor how many data sources are necessary to tell the story. The AWWA 2021 State of the Water Industry report [1] paints a clear picture of the complex challenges before today's water/wastewater utility oversight bodies. Aging infrastructure, capital improvement financing, long-term water supply, emergency preparedness, watershed protection, aging workforces, regulatory compliance, groundwater management, emerging regulations, cybersecurity, cost recovery, talent attraction, asset management, customer relationships, water loss — the breadth and depth of management, finance, and technical decisions demanded of today's oversight bodies is daunting. This decision complexity is further complicated by the lack of requirements for technical expertise to serve on City Councils, County Commissions, and many Boards of Directors. In The Psychology of Human-Computer Interaction, Newell, Card, and Moran [2] present a description of the Hick-Hyman law [3,4] which postulates the time to make a decision is a factor of the number of choices and the probability of occurrence of each choice. For any single technical issue a utility oversight body considers, there are (practically) multiple potential choices and (theoretically) an infinite number of choices. When considering stratified decisions, such as a simultaneous (1) water rate increase with (2) an assessment of water affordability and (3) the reduction of aged infrastructure backlog, no decision-time model exists that dependably describes the resulting decision timeline. What every utility executive knows is that the time-to-decision on any one of these issues is significant. In October 2019, Opelika Utilities (Opelika, Alabama) presented their Board of Directors with a Capital Strategic Plan that assessed the requirements for full lifecycle replacement of all horizontal assets. The assessment identified a rate of replacement that would require a 5X multiplier when compared to the current annual capital asset replacement program. General Manager Dan Hilyer, PE, identified the following critical decisions that would need to be made within the first years: 1.Fund the immediate replacement of 100% of system water meters with an Advanced Meter Infrastructure (AMI) system; 2.Establish the long-term disposition of the system's most aged water treatment plant; 3.Fund refurbishment of the aged plant or the design of a similar replacement plant; 4.Establish a timeline to fully fund all reserve accounts; 5.Establish a policy to minimize the long-term cost of money; 6.Establish an approach to resolve taste and odor; 7.Establish a capital improvement program sufficient to meet lifecycle replacement for 100% of horizontal assets; and 8.Establish an appropriate water rate to fund the other objectives. As of October 2020, the Opelika Board of Directors had accomplished only one of the necessary critical decisions, funding of the AMI project. Without an acceleration in the decision velocity, the necessary decisions to manage aged asset backlog, water affordability, aging workforce impacts, emerging contaminants, taste and odor, and many other challenges would be at risk. The very sustainability of Opelika Utilities hinged on the ability to accelerate all of the complex decisions before the Board of Directors. With a newly established enterprise data warehouse that delivers data across all of Opelika Utilities' data sources to the management team in real-time, the Opelika Utilities General Manager recognized an opportunity to establish a vision to accelerate Board of Directors decision velocity through the utilization of real-time data storytelling. The following regular Board decisions were identified to be included in the initial dashboard iteration: - Annual water rate setting; - Annual Capital Improvement Program; - 5-Year Capital Strategic Plan; - Annual analysis of water affordability; - Monthly management of the long-term cost of money; - Management of the aged infrastructure backlog; - Annual management of reserve financial accounts; - Annual budget setting; and - Long-term water rate and water affordability management. This approach to data storytelling requires the real-time delivery of data from the following data sources: 1.General Ledger; 2.Budget; 3.Geospatial; 4.SCADA; 5.Billing; 6.Metering; 7.Work Orders; 8.Service Requests; 9.Inventory; 10.Capital Assets; and 11. Human Resources. Opelika Utilities utilized this new capability and paired it with the following principles of dashboard design: 1. Provide the Board of Directors with the decision narrative; 2. Create perspective of importance for each decision; 3.Provide clarity of current state and desired objectives; 4.Demonstrate connectivity of decision points; 5.Provide feedback for all decision points; 6.Demonstrate consequences of decisions and present alternatives; and 7.Accomplish all objectives in real time. The resulting dashboard for the Opelika Utilities Board of Directors is providing a transformative experience in decision-making. Data storytelling provides the Board of Directors with a clear narrative and metrics to reduce long-term water rates, increase affordability, have confidence in the capacity of the water system, and minimize the short-term cost of borrowing money. The approach to data storytelling even gave the Board enough confidence to adopt a real-time automated variable water rate that equitably recovers the true cost of both water production and water service. The Opelika Utilities Board of Directors now makes multiple critical decisions each month — without hesitation — with full confidence and clear perspective. This technical presentation will tour through several of the data story dashboards used by Opelika Utilities, provide a brief overview of the business intelligence delivery platform that spans all utility data sources, and discuss the specific benefits realized by each story dashboard.

The District of Columbia Water and Sewer Authority (DC Water) currently oversees over $7.5 billion in assets and manages a ten-year Capital Improvement Program (CIP) with a budget exceeding $5 billion. To that end, DC Water launched a District-wide inspection program in the Spring of 2022 that aimed to inspect 40 miles of sanitary and combined sewers between 12 and 60 inches in diameter each fiscal year. Findings from these inspections would be used to identify and prioritize assets for rehabilitation under the CIP. Performing inspection work in any major city is no easy feat. Performing inspection work in the District of Columbia, one of the most densely populated cities in the United States that also houses a plethora of federal agencies and military bases, presented a multitude of unique complications. Along with more typical road blocks such as aging infrastructure leading to emergency repairs and unmapped assets discovered in the field, the surrounding stakeholders and property owners affected by the inspection program included foreign embassies, government agencies, the US Secret Service, Joint Base Anacostia-Bolling, the National Park Service, the Smithsonian National Zoo, the DC Department of Transportation, a prison, and even disgruntled homeowner associations, to name just a few. The project team expertly handled an assortment of communications for permit acquisitions, access coordination, and stakeholder outreach. As if these circumstances were not challenging enough, the procurement timeline resulted in a tremendously accelerated inspection schedule during which 40 miles of inspection work had to be prioritized, performed, reviewed for quality, and invoiced all within the last five months of the fiscal year. Through an innovative use of new software tools, and copious amounts of coffee, this seemingly impossible feat was accomplished on time and on budget. The project team employed several programs and technologies to efficiently process inspection media and data in order to meet the ambitious deadline. T4 Spatial's inspection management platform, t4 Vault, allowed the inspection contractor to easily upload inspection submittals to the quality reviewer. The platform's user-friendly display showing the inspection media and reports side-by-side greatly facilitated quality assurance and quality control (QA/QC) reviews. Additionally, InfoAsset Manager (IAM) was deployed in conjunction with t4 Vault to perform corrections to the NASSCO PACP and MACP databases. IAM also possessed useful capabilities to export tracking sheets documenting the status of inspections and inspection reviews. In the field, the project team employed the use of the Fulcrum app for field inspectors to easily submit daily logs and field entries. Crews also collected GPS using Terraflex. Dashboards using ArcGIS Online were developed to convey the most up-to-date inspection data in an easy-to-understand quantitative and visual format to the utility owner. The inspection program is now wrapping up its second fiscal year of inspections and, to date, has completed over 100 miles of pipe inspections and 3,000 manhole inspections.

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

The City of Spokane (City) owns, operates, and maintains the wastewater and stormwater collection systems (collection system) in Spokane. These systems consist of a variety of assets and facilities, and accomplish the important purposes of:
-- Collecting and conveying wastewater from residents and businesses, along with stormwater runoff from areas with combined sewers, to Riverside Park Water Reclamation Facility (RPWRF) for treatment and discharge.
-- Collecting and conveying stormwater runoff from surfaces throughout the City for at least partial treatment and discharge.
Stormwater is discharged to a variety of endpoints, including the Spokane River (as part of the City's municipal separated storm sewer system [MS4]), into the ground (via bioretention and underground injection wells, also known as dry wells), or evaporated. Both the wastewater and stormwater systems have historically been operated with minimal data collection and supervisory or remote control capabilities, primarily because the assets and facilities have generally been achieving their desired performance. However, the City has long recognized the potential for improved performance of the collection system through the implementation of supervisory control and data acquisition (SCADA) for the collection system (referred to as the 'collection system SCADA'). The collection system SCADA will allow for increased monitoring and alarming, improved data management, and the potential application of real-time control (RTC) at combined sewer overflow (CSO) control facilities and interceptor protection tanks (IPTs). These improvements will result in reduced CSOs, reduced risk of sanitary sewer overflows (SSOs), more efficient operations and maintenance (O&M), and an increased understanding of how the system operates. Implementation and operation of the collection system SCADA would also have staffing and cost (capital and O&M) impacts on the City that need to be considered. Now that the City has constructed large and complex CSO control facilities and IPTs throughout the City as part of complying with the City's Waste Discharge Permit for CSOs and the RPWRF, the City has prepared a Collection System SCADA Master Plan (Master Plan), completed in May 2019. The purpose of this Master Plan was to:
-- Identify and evaluate potential opportunities for RTC at CSO control facilities and IPTs that could be implemented in the future, and assess costs and staffing impacts
-- Identify and prioritize monitoring and alarming improvements to the collection system, and assess costs and staffing impacts
-- Identify SCADA network and infrastructure needs to support the implementation and operation of the monitoring, alarming, and RTC improvements identified, and assess costs and staffing impacts

Establish an implementation roadmap for the selected collection system SCADA improvements and assesses the capital, O&M, and organizational impacts of implementing the recommendations As part of the Master Plan, the project team developed a system model of the City's sewer system, and simulated possible RTC scenarios to manage wet weather events. The model results indicated a reduction in CSO volume of between 30 to 40 percent, as shown in Figure 1, depending on the storm and level of RTC implemented. Not only did RTC reduce CSO volumes, but it also allowed for better protection of critical points in the interceptor system that are susceptible to surcharging. In conclusion, this project established a clear and implementable path forward for the City to implement SCADA in their collection system. The SCADA system will provide benefits on many fronts -- CSO reduction through RTC, improved O&M and performance due to real-time data collection, and improved reporting. This presentation will focus on describing the gaps and solutions identified in the Master Plan, with a particular focus on discussing the RTC analysis and results, and presenting the anticipated O&M impacts of making the improvements. This completed project was unique because it focused on using RTC as an adaptive management strategy for completed CSO control facilities. Many other municipalities are now in similar situations, where they have finished building CSO control facilities and are dealing with what to do if the control facilities are not sufficient to meet CSO reduction standards. This project provides an example of retrofitting completed facilities with RTC and monitoring in order to improve performance. Following the completion of this project the City has moved forward with designing and constructing the collection system SCADA, and will be making monitoring improvements at several high-priority pump stations and CSO control facilities.

Sewage drop shafts function as a powerful air moving devices by creating water-in-air waterfalls that move air like fans or air-in water fluid columns that transport and compress quantities of air when water velocities are greater than the bubble rise velocity. This creates situations where air in unvented tunnels can transfer pressure at the sewer obvert to the surface at shafts that, even when vented can lead to situations where air and water forcefully exits manholes at the surface and damages surrounding infrastructure (Figure 1). This damage can be severe in large wet weather events. One such event was in St. Louis Missouri on August 30, 2021, which caused a precast drainage structure top to separate from the main structure (referred to herein as the Ikea shaft, the result being visible in Figure 2 below). Another depressurization at Arkansas and McKean caused damage to the pavement near a drop shaft and is generally a nuisance to residents. For the Ikea shaft, SWMM models for the area were analyzed to estimate hydraulic flow through the sewers during cloudburst events. This accompanied creation of an inventory of all drop shafts associated with the tunnel of interest using record drawings. Model results were superimposed onto the inventory to determine how flow enters the deep tunnels, the quantity of flow at each inlet and outlet, and identify manholes where no flow enters the sewer from above. This review identified that the Ikea shaft was the first (in the direction of flow) that did not have flow from above that could otherwise prevent air pressure at the sewer obvert transferring to the surface, and that over half the drop capacity of the deep sewer system is upstream of the Ikea shaft.A previous evaluation of the structure had been performed. This investigation concluded that the drop shaft experienced a rise in the hydraulic grade line during wet weather, which caused the overflow events. As a result, a grate vent (visible in Figure 3) was installed on the structure. This helped mitigate issues, but a rising hydraulic grade line did not explain ongoing cover slab displacements. It was determined that the investigation had not directly considered the deep sewers upstream of the Ikea shaft, vent locations, and steady-state phenomena like air flow and entrainment effects. In response to these observations, one-dimensional model of the deep sewer system connected to the Ikea shaft was to estimate maximum entrained air flow rates based the geometry of the deep sewers and connected shafts (long section shown in Figure 4). To estimate maximum entrained air flow rates a pressurization model was developed by doing the following: - Derived simplified pressure loss/gain relationships for the sewers and drop shafts - Assuming bubbly or misty flow with air and sewage velocities equal. - Allowing for the compression/expansion of air along/down sewers/drops and the resulting change in mixture velocity along/down sewer/drops and the resulting impact on pressure loss/gain. - Based on conventional Colebrook-White friction factors and average fluid properties. - Forwards-calculated sewer flow rates based on input sewage and air flow rates at each drop. - Back-calculated sewer obvert pressure from the outfall to the sewer obvert for each drop based on the forwards-calculated flow rates, with iteration to allow adjustment and resolution of the resulting mixture fluid properties. - Used the derived pressure loss/gain relationship for the drops to calculate an air-sewage mixture column depth/height that would give the back-calculated sewer obvert pressure. - Used Newton's method to adjust the input air flow rates to give an air-sewage mixture column surface at drops below the incoming sewer invert by the distance necessary for the sewage to free fall to the mixture velocity at the column surface (as indicated in Figure 5). - With minimal sewage flows in drops downstream of the Ikea shaft, varied upstream sewage flow rates to indicate entrained air flow rates that could supplied to the Ikea shaft and the pressure at which they could be supplied (plotted in Figure 6 for three scenarios due to uncertainty of the exact location of the Ikea shaft in the network). A simplified model was selected for the evaluation because higher air entrainment rates are not considered plausible as there would be no driving force for air entrainment. The driving force for air entrainment is taken to be the deceleration of free-falling sewage entering the air-sewage mixture column. Maximum possible air entrainment is conservatively taken to be the air entrainment rate that gives an air-sewage mixture surface level at which there is no longer any free-falling sewage deceleration energy to drive air entrainment. Physically achievable air entrainment rates will be lower due to some energy being required to drive entrainment and overcome bubble rise velocities. This allowed for a flexible model that did not have high computational costs.↵ The model calculated that the maximum entrained air flow rates increase with obvert pressure before peaking and then declining with increasing obvert pressure, which is shown in Figure 6. These pressures were calculated to be well above the lifting pressure of cover slabs. Adequate venting of entrained air flow would be required to prevent high pressures developing under cover slabs. The analysis concluded that the historical depressurization incidents were a result of high entrained air flow rates and obvert pressures forcibly venting at the Ikea shaft. This location forcibly vents because the site lacks sufficient sewage inflow to prevents the obvert air pressure transferring to the surface. Being the first such shaft (in the direction of flow), it likely protected other downstream shafts without inflow that have a pressure retaining design. Other downstream drop shafts could also have a large vent grate or are much further downstream where obvert pressures are much lower and would therefore be less likely to violently depressurize. The maximum entrained air flow rates for the Ikea shaft indicated an order of magnitude increase in venting area was required. To mitigate this issue, GHD designed the new shaft cap in Figure 7 for the Ikea shaft with more than an order-of-magnitude increase in venting area, increased weight and some pressure balancing that reduces the net lifting force. This design enables a two orders-of-magnitude increase in the air flow rate that can be vented when compared with the previous cover slab (Figure 3). This was a relatively inexpensive modification that did not require complex models or deep energy dissipation structures to design and install. The methodology could be applied to similar sewers to assist with venting analysis and design without the need of more complex and computationally intensive modeling techniques. Modifications are currently in design and are expected to be installed prior to the conference.

With many municipalities having excess anaerobic digester capacity, anaerobic co-digestion (AcoD) provides an opportunity to improve biogas recovery while potentially reducing landfilling of organic municipal waste streams. In the United States, 12% of municipal solid wastes are yard trimmings (YT), which are often sent to landfills or composting for disposal (US EPA 2021a). However, YT landfilling and composting releases 475-1100 and 20-130 kg CO2 eq. per dry ton of fugitive methane (CH4) and nitrous oxide emissions per year, respectively (Brown and Chang 2014; Zhu-Baker et al. 2017). Utilizing yard trimmings as a co-digestion stream improves energy recovery, meets higher renewable energy credits (REU) credit standards than food waste and fats/oils/grease, and reduces climate impact due to fugitive emissions of CH4 and N2O. In this work, we developed nature-inspired bacterial enrichments for cellulose degradation and use them to pretreat common yard wastes to the Southwest and a stock chemical cellulose mixture. We evaluate the impacts of pretreatment using our inoculum and its improvement of CH4 production and landfilling offsets through sludge reduction as part of AcoD with thickened sludge. We cultivated lignocellulose-degrading batch inoculum over 10 generations based on feces obtained from Oryctolagus cuniculus domesticus, who primarily eat hays, grasses, and leafy matter with a digestive retention time of about 4 days. The inoculum were exposed to a variety of typical Phoenix yard waste & lantana and grass & or purchased cellulose. Each generation of inoculum was inoculated for 10-14 d, and then 1/10 of the total volume was added as seed for the next inoculum generation. An inoculum was used as the seed for fermenting reactors with 5-14 d hydraulic retention times (HRTs). Rehydrated plant matter was fed into the fermenters at 40 to 80 g DW/L each of lantana, grass, and cellulose. Fermented material was also fed to anaerobic co-digesters. Thickened sludge and seed anaerobic digester inoculum were provided by the City of Mesa, Arizona's Northwest Water Reclamation Plant (MNWWRP). To test pretreatment coupled with anaerobic digestion, AcoD reactors were fed the same amount of thickened sludge as the control plus an additional amount of material from the fermenters to maintain a 19.2-d HRT. We had two controls in the system: (1) only thickened sludge fed to control reactor was operated at a 25-d HRT to mimic MNWWRP; and (2) the same amount of thickened sludge was fed as a control plus 80 g DW/L undigested plant matter at a 19.2-d HRT. The reactors were allowed to operate at least 3 HRTs to achieve steady state prior to taking the data reported here. To ensure reactors would not sour, the pH in all reactors was kept at 7.5 ± 0.2 using NaOH for pH adjustment and CaCO3 to improve buffering capacity. We monitored pH, total and soluble COD (TCOD; SCOD), total and volatile solids (TS; VS), CH4, hydrogen gas, the volatile fatty acids (VFAs) of formate, acetate, propionate, butyrate, valerate, and caproate, and lignocellulose content based on an Ankom 2000 fiber analyzer. YT prefermentation provided increased solubilization of plant matter to VFAs and with negligible biogas production. For example, VS decreased an average 29% at a 14-d HRT with 80g DW/L loading of YT. At the same time, SCOD increased 20% leaving the reactor, with 6.3% being converted to VFAs. While the analysis is still in process, it appears that proteins in the leaf matter and some hemicellulose were hydrolyzed to soluble forms. Our initial results show that AcoD fed prefermented YT has higher CH4 production and better volatile solids reduction than the control or AcoD with untreated YT. As an example using the prefermented YT discussed above, Figure 1 shows that AcoD fed prefermented YT and thickened sludge averaged the highest CH4 production, 330 mg CH4/d, versus 270 mg CH4/d for the control and 160 mg CH4/d for AcoD with untreated YT. The AcoD with prefermented YT also achieved the highest sludge reduction, 52%, versus 40% with the control and 43% AcoD with untreated YT. At the same time, the AcoD with prefermented YT had a lower yield of CH4 per g VS reduced (610 mL CH4/g VS) versus the control (914 mL CH4/g VS). This lower yield is likely due to lignocellulose being highly recalcitrant. The encouraging results with AcoD fed prefermented YT could have far reaching impacts on the wastewater and AcoD community. Based on these results for 4000 m3 (~879,000 gallon) capacity anaerobic digester, AcoD fed prefermented YT produces 184,000 m3/yr more CH4 than the control and 805,000 kg/yr of YT diverted from landfilling. In addition, the gas produced from YT qualifies for D3 cellulosic RIN credits as part of the EPA's Renewable Fuel Standards program versus other co-digestion streams like food waste and fats/oils/grease (FOG), which qualify for D5 RIN credits. Based on September 20, 2021, data, D3 RINs were worth $1.13 more than D5 RINs (US EPA 2021b).

Over 54,000 community water systems face the inevitable cost of pipe repair and replacement. The United States EPA states that nearly 60% of the total system costs are found in the distribution and transmission pipe lines. Infrastructure asset management is an approach which can help utilities bring together the concepts, tools, and techniques to manage assets at an acceptable service level at the lowest life-cycle cost. The water industry has seen many types of academic surveys and studies on water main replacement programs and the benefits of asset management and prioritization. However, many utilities have not historically tracked all of the elements of water main break data. Over the past 20 years, most utilities have come to realize the importance of tracking all aspects of their infrastructure in a GIS system and have records of what kinds, sizes, and repair history of all pipes. As this trend continues, more data and analysis will be available to the industry to improve water distribution system repair and replacement decision making. One factor used to quantify the occurrences of failing underground pipe networks is water main break rates. Water main break rates are calculated for all pipe materials used in water delivery to create a measurement to judge pipe performance and durability. Water main break rates can vary year to year and by utility. However, in aggregate, break rates produce a compelling story which can aid our prudent decision making as it relates to repairing and replacing our underground pipes. This presentation reviews the newest water main break study metrics and findings including comparisons between typical surveyed data to actual AI/Machine Learning findings which can also help benchmark an organizations' break rates.

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

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

The City of Chelsea, MA is strategically located as a gateway between downtown Boston and North Shore communities and is home to a vibrant, diverse population and industry that contribute significantly to the overall wealth of the region. Chelsea is served by the Massachusetts Water Resources Authority (MWRA) for water supply and wastewater collection. Many MWRA interceptors and a major regional headworks and pumping station are located in Chelsea. Like many other coastal communities in New England, Chelsea is serviced by a mix of combined and separated sewer systems that were built more than a century ago and are at the end of their service life. This outdated infrastructure hinders new development and growth, especially in the context of increased precipitation and coastal-induced inundation risk due to climate change. As a response to this concern, Chelsea has embarked on a city-wide master plan for sewer separation and infrastructure upgrades to systematically work towards attainment of the following three main goals: 1. Allow for future growth by progressively upgrading drainage infrastructure able to accommodate future population and increased stresses from climate change; 2. Eliminate CSOs by separating existing combined sewer areas and; 3. Reduce inflows to sanitary pipes from public and private properties that currently decrease available system capacity and increase operating costs to the City. In order to create this ambitious program, a significant modeling effort was carried out following a multi-step process. The first step consisted of building and calibrating a city-wide drainage model to help understand points with weak level of service and estimate peak flow and volumes reaching the MWRA interceptors and combined sewer overflows during dry and wet weather events. The City-wide model was built in Infoworks ICM using pipe network data from multiple sources such as record drawings, GIS, field inspections, and recently collected ground-level LiDAR information captured city-wide. The second step of the process consisted of developing conceptual level pipe layouts with the goal to achieve sewer separation city-wide and improve level of service. The conceptual level plans were developed using a 'best case scenario' approach (i.e. assuming an ideal drainage network can be built without necessarily accounting for other factors such as utility conflicts or permitting issues for new outfalls). The reasoning behind this approach was the desire to delineate a network able to attain optimum hydraulic performance based on natural topography and street layout and then work backwards, if needed, when conflicts identified during later phases of the process require this layout to be modified. The conceptual storm and sanitary systems were then incorporated into an Infoworks ICM model, which was used to fine tune the conceptual network (e.g. pipe slopes, pipe sizes necessary to provide the desired level of service or flow velocities for a given event). The third step was a planning level engineering effort where a street-by-street evaluation at each sewershed was performed. The feasibility and actions needed to go from the current condition to the proposed condition in the conceptual model were evaluated and alternative actions proposed when identified conflicts could not be resolved. The fourth and final step consisted of packaging and phasing the execution of the sewer separation and inflow reduction projects based on feasibility, City's priorities and constraints, as well as interim system conditions. This product is the City's new Master Plan for Sewer Separation and Drainage Infrastructure Upgrades, which will provide a systematic approach to drainage infrastructure improvements over the next few decades.

The Narragansett Bay Commission (NBC) owns and operates Rhode Island's two largest wastewater treatment plants along with extensive infrastructure of interceptors, pump stations, and combined sewer overflow (CSO) structures. In 1992, NBC entered into a Consent Agreement with Rhode Island Department of Environmental Management (RIDEM) that established a three-phase CSO control plan with the goal of reducing annual CSO volumes (98%) and shellfish bed closures (80%). Phases I and II of the CSO Control Program were completed in 2008 and 2015, respectively. Phase III, the final phase of the program, commenced with a re-evaluation of the original plan in 2015, including a financial capability assessment to incorporate NBC's affordability goals into the Phase III implementation schedule. Phase III final design phase started in 2018 for 12 projects, and the first projects started construction in 2021. The largest of these projects is the 2-mile long, 30-ft finished diameter, 150-ft deep rock Pawtucket CSO storage Tunnel, which is being delivered as a design-build project. The tunnel construction is scheduled to be completed in early 2024, and construction of the tunnel dewatering pump station and screening facility will start in early 2024. This presentation will provide a program progress update, diving into construction challenges and lessons learned including the following: -Sequencing of design of tunnel with follow-on work: design development of tunnel elements at interfaces with surface projects; -Regulatory coordination: multiple approvals and permits in a dynamic project delivery environment; -Management of excavated tunnel material: what do you do with one million tons of 'muck'? -Material and labor cost escalation: balancing schedule vs. cost impacts to labor and materials; -Groundwater dewatering and treatment: approach to managing and pre-treating groundwater from large excavations prior to discharge; -Inspection and repair of existing Providence Tunnel: taking a look at condition of the existing tunnel in operation since 2008. The presentation will conclude with a look ahead to the schedule for completion of the remaining near surface projects and anticipated commissioning and start-up of the Phase IIIA system in 2027.