CVWRF CAPTIAL IMPROVEMENTS
CVWRF, with the assistance of a national engineering firm, recently completed a Condition Assessment and Asset Management Plan (AMP) for its wastewater interceptor piping and treatment plant to identify the renewal needs of the system’s 30-year old infrastructure. The AMP identified an estimated $150 million in necessary restorations to CVWRF’s collection system piping and treatment facilities that will be needed over the next 20 years to serve the local community through the year 2035. The improvements will replace aging and degraded mechanical and electrical equipment in the treatment plant and rehabilitate corroded collection system pipes to meet the future needs of our community and ensure compliance with State and Federal regulatory requirements.
In addition, the State of Utah Division of Water Quality (DWQ) recently adopted a new rule (The Technology-Based Phosphorus Effluent Limits or TBPEL Rule, R317-1-3.3) that requires wastewater facilities to install processes that remove phosphorus from their effluent discharge. The DWQ has also lowered permit limits for ammonia and several other pollutants in CVWRF’s effluent discharge. To comply with the new TBPEL Rule requirements and lower permit limits will require CVWRF to upgrade the treatment process at an estimated cost of $100 million over the next 7 years. Once the existing facility rehabilitation and upgrades to remove phosphorus and other pollutants are completed, CVWRF facilities will be ready for the next 30 years of service.
The major improvements that are under design and construction in the near term are listed below. Other improvements beyond these are also being planned for over the next 20 years and will be added to this list as project planning progresses.
- Cogeneration Engine Replacement and Upgrades (2017-2019)
- Biological Nutrient Removal (BNR) Secondary Treatment Process Upgrade (2017-2025)
- Secondary Clarifier Expansion (2018-2019)
- Blend and Equalization Tank Rehabilitation (2017-2018)
- Side-stream Nutrient Removal Systems (2020-2024)
- Upgraded Reuse Water Filtration System (2018-2020)
- Rehabilitation of the interceptor pipeline system (2017-2020)
- Rehabilitation of the Headworks Screening Process (2018-2019)
- New Odor Control System (2018-2019)
The improvements listed above are described in more detail below.
The CVWRF has successfully operated a cogeneration facility since it was initially constructed in the 1980’s. The existing engine generators are now obsolete and maintenance parts are increasingly difficult to obtain. In addition, the current equipment is very inefficient and produces higher levels of exhaust pollutants than new engine generators. This project will replace the existing engine-generators with new and more reliable advanced reciprocating engines with high electrical efficiency and low exhaust emissions. The engine replacement project will also increase generation capacity and reliability, aiding CVWRF with moving closer to its goal of becoming energy-independent. The project also includes replacing and expanding the digester gas treatment and compression system to support the new engines. The new engines have been purchased from General Electric Jenbacher and have been delivered to the CVWRF plant.
Biological Nutrient Removal
In 2014 the Utah Division of Water Quality adopted a new rule called “Technology Based Phosphorus Effluent Limits” (TBPEL) governing the discharge of phosphorus from wastewater treatment facilities in the state. The rule requires all mechanical treatment plants to discharge less than 1 mg/L of total phosphorus in their effluent on an annual average basis by 2020. The CVWRF has been granted a variance from the original compliance date and is required to meet the 1 mg/L limit by 2025. In addition to this rule, the DWQ has adopted a policy of granting extensions to potential future effluent nitrogen requirements if treatment facilities optimize their processes to remove nitrogen containing compounds. CVWRF has conducted extensive evaluation of nutrient reduction technologies and treatment processes since 2014 and has developed a biological nutrient removal process that is currently being designed and will be constructed between 2020 and 2025 to meet the new requirements.
Biological nutrient removal (BNR) removes total phosphorus (TP) and total nitrogen (TN) from wastewater through the use of microorganisms grown under specific environmental conditions in the treatment process. There are a number of BNR process configurations available. The CVWRF recently completed an intensive pilot study to select the optimum process configuration for treating wastewater with the unique characteristics of the water received at the CVWRF treatment facility. The pilot plant to test various BNR configurations was run during the spring, summer and fall of 2017 and the new process is currently being designed for full scale implementation. The design process with take two years (2018 and 2019) to complete and then the design drawings and specifications will be bid to prequalified contractors for construction. CVWRF has completed a contractor prequalification process as part of the predesign process evaluation.
The first step in the implementation of a BNR process is to expand CVWRF’s secondary clarification process capacity. The CVWRF currently operates eight 125-foot diameter center feed clarifiers and two 125-foot peripheral feed clarifiers. The new BNR process will require two additional clarifiers to optimize the solids concentration in the BNR aeration basins, the solids loading rate on the clarifiers, and improve clarifier process redundancy. These new clarifiers will be added in 2008-2019 ahead of the main BNR process construction to improve overall plant reliability and allow for early construction of the clarifier project without extensive coordination with construction of future BNR facilities.
Blend and Equalization Tank Rehabilitation
The blend and equalization tanks are 350,000 gallon raw sludge and digested biosolids storage tanks. These tanks were constructed in the 1950’s and will be incorporated into the new BNR process as raw primary sludge fermenters. Sludge fermenters are needed to produce volatile acids (acetic acid or vinegar) which is used by the phosphorus removing microorganisms in the BNR process. Because of their age and past use for sludge storage where they were exposed to corrosive hydrogen sulfide gas, the two tanks are in need of rehabilitation and replacement of their covers. This project will rehabilitate the two tanks by sandblasting and coating the insides with an acid resistant epoxy coating and replacing the existing corroded steel covers with stainless steel covers.
Side Stream Nitrogen Removal
As part of the transition of CVWRF to a BNR treatment facility, CVWRF will construct side stream phosphorus and nitrogen removal processes to remove these nutrients from the belt press filtrate and prevent their recycle back to the head of the liquid treatment process. This is important because recycle streams contribute about 20 percent of the total nutrient load on the liquid treatment process. Removing nutrients from the concentrated recycle streams will lower the overall size and cost of the BNR process.
Many side stream nutrient removal processes have been developed over the past decade in response to reducing the cost of mainstream nutrient removal. They include both physical-chemical and biological and processes. Chemical processes are commonly used for phosphorus precipitation. Chemical phosphorus removal processes add magnesium and raise the pH which precipitates phosphorus and a portion of the ammonia as the mineral struvite (magnesium ammonium phosphate). Biological processes now dominate the market for nitrogen removal and the most cost-effective side stream technologies have been shown to be those based on anammox bacteria which shortcut the traditional nitrification-denitrification reaction and are thus more energy efficient. This will be the technology that the CVWRF will be implementing for ammonia removal.
The CVWRF is evaluating alternatives for constructing a new reuse water filtration system. The CVWRF currently uses disinfected secondary effluent for plant water needs and to supply Tyupe I reuse irrigation water to the Central Valley Golf Course. The plant water (3W) is strained through automatic backwashing strainers and the irrigation water is filtered through an upflow sand filter. Due to land requirements for construction the future nutrient removal facilities, the existing upflow sand filters will need to be demolished.
The new filtration system will include a filter building, rotating disk filters, sodium hypochlorite feed system and pumping systems. The existing reuse UV disinfection system will also be moved to the new filter building. The intent is to filter and disinfect all plant water and irrigation water delivered to the golf course to meet Type I reuse standards. The CVWRF is currently in the process of designing the new reuse filter system.
The interceptor pipelines and the influent channel are concrete structures that collect wastewater from the member entity collection systems and deliver it to the headworks building. At the downstream end of the interceptor piping system the pipes terminate at a large underground rectangular channel. The channel delivers the water to the treatment plant site where it is split into three 90-inch concrete pipes that go into the headworks building. Due to deteriorating conditions of the interceptor lines, channel and 90-inch pipes, due to corrosion by hydrogen sulfide gas released from the raw sewage, rehabilitation of these structures is needed. Portions of the interceptor have been rehabilitated in the past. Rehabilitation of the remaining structures commenced in the fall of 2017.
Headworks Screening System Rehabilitation
The headworks screening system and associated screenings and grit conveyors and processing equipment have been in continuous use for over 30 years and are now worn out. This equipment is critical for protection of downstream processes and must be replaced. Since the original system was installed there have been significant improvements in headworks equipment. CVWRF is currently in the process of identifying and evaluating new equipment to replace the existing systems. The replacement of headworks equipment is scheduled to occur in 2019-2020.
Influent wastewater entering the headworks and certain treatment process streams such as sludges contain constituents that generate strong odors and corrosive hydrogen sulfide gas. Providing active ventilation of the space above the wastewater in the influent channels and certain sludge processing tanks can capture the foul air and allow treatment to eliminate the odorous compounds and reduce the potential for corrosion. While the CVWRF does not currently use an odor control system to treat foul air from various plant processes, new odor control facilities are being developed to address these concerns. Removing odorous air from the influent channel, headworks, sludge fermentation tanks, and sludge thickening facilities will help to protect equipment and provide a safe working environment for the plant staff. Design of a biofilter to treat foul air has been completed and will be bid out in the early spring of 2018.