Loudoun Water: Planning for an Evolving Future
- Janice Carroll, Phill Yi, Wendell Khunjar, Ron Taylor, Paul Pitt, Sarah Lothman, Mike Latham, Mike Rumke
The Broad Run Water Reclamation Facility (BRWRF), owned and operated by Loudoun Water, is an 11 mgd advanced treatment facility that employs a 5-Stage biological nutrient removal (BNR) process, followed by membrane filtration and granular activated carbon (GAC) to meet monthly effluent concentration limits. The BRWRF must also comply with annual nutrient waste load allocations of 134,005 lbs total nitrogen (TN)/year (4 mg TN/L at 11 mgd) and 3,350 lbs TP/year (0.1 mg TP/L at 11 mgd). The BRWRF also provides reclaimed water for cooling tower purposes.
By 2014, the BRWRF was operating at approximately 50% and 75% of the of the installed liquid and solids design capacities, respectively. Due to rapid and continued growth in the service area, Loudoun Water was faced with liquids and solids capacity limitations and needed to consider expansion of the overall treatment facility. Loudoun Water commissioned a master plan to ensure that decisions made regarding expansion and implementation of new technologies at the BRWRF would be compatible with the long-term future of the BRWRF facility.
This presentation will document the master planning process utilized and provide insights into flexible implementation strategies that can be used to position utilities for compliance in an ever evolving regulatory world.
Status of work – The master plan was completed in December 2016. Demonstration of innovative technologies/concepts will be ongoing through 2017.
The planning process was iterative in nature to allow for the development of strategies that would provide maximal flexibility to Loudoun Water.
• Phase 1 involved fully understanding the existing BRWRF with a view to optimizing existing assets. A calibrated whole plant process model, computational fluid dynamic model, and financial model were developed.
• Phase 2 involved exploring the world of options related to treatment technologies and business solutions that might be applicable to the BRWRF (inside and outside the fence line). Feedback regarding decision criteria was also obtained.
• Phase 3 utilized calibrated modeling, parametric design, cost estimation and piloting in conjunction with a customized quadruple bottom line (QBL) framework to develop and evaluate numerous strategies that would allow Loudoun Water to meet growth and economic development needs, while best leveraging existing assets, external treatment and nutrient management options, new and maturing technologies, and resource recovery and energy management opportunities AND protecting the environment and public drinking water supplies.
This approach was utilized to develop solutions for immediate (2015 to 2020), near-term (2020 to 2040) and long-term (2040 to 2070) timeframes. All solutions were checked against each other to ensure compatibility and avoid selecting strategies that limit flexibility in the future.
Selected Outcomes from the Planning Process
Interim solids management
Options, ranging from hauling offsite to implementation of thermal hydrolysis, were considered. Both cost and non-cost criteria evaluations indicated that additional anaerobic digestion volume was the preferred solution due to its conformance with the long-term vision of Loudoun Water.
Long-term solids management
Residual management in Virginia is expected to be impacted by emerging regulations that will drive a need to generate Class A biosolids and eventually transition away from bulk land application. Implementation of sludge pre-treatment technologies (e.g., THP) will facilitate increase digester gas production, reduce disposal mass, reduce digester volume, increase sludge dewaterability, and produce a Class A sludge. However, sludge pretreatment process will result in the production of refractory organic compounds, which will impact the ability to meet effluent TKN and COD limits.
Loudoun Water also has the flexibility to retain anaerobic digestion (no THP) as the sole means of solids stabilization. If this occurs, implementation of a thermal dryer will be required in order to produce Class A solids. If/when bulk land application is not possible, implementation of thermochemical oxidation (e.g., gasification) will be required.
Meeting stringent nitrogen limits
A full-scale demonstration was performed and indicated that the current configuration can meet a final effluent TN and TKN of approximately 2.0 mg/L and 1.0 mg/L respectively. Achieving 2 mg TN/L requires that that the BRWRF maintain dissolved organic nitrogen (DON) removal across the GAC. If THP process is implemented, there may be a need for enhanced tertiary treatment to manage the recalcitrant organic nutrients.
Reducing operating costs
Next generation nutrient removal was included in the facility expansion implementation plans. A phased approach is proposed whereby dynamic dissolved oxygen control strategies would be implemented in the immediate and near-term. Implementation of mainstream deammonification is proposed after testing verifies cost savings and the ability to meet the stringent effluent TKN limit. As a baseline, sidestream deammonification is proposed in the immediate and near-term.
Water – The BRWRF already produces non-potable reclaimed water that is used for cooling towers and other non-potable uses. In the near-term, the reclaimed water strategy calls for Loudoun Water to continue serving industrial needs, but mitigate the impacts of return stream total dissolved solids and recalcitrant nutrient fractions. In the long-term, the BRWRF will continue to have the ability to produce water for indirect potable reuse.
Phosphorus – Phosphorus is currently removed using a combination of chemical and biological processes. In order to facilitate phosphorus recovery from this matrix, flexibility is provided to allow BRWRF to implement technologies that recover phosphorus directly from sludge; however, implementation of these technologies will only be triggered when the benefits of recovery exceed the costs associated with technology implementation.
Energy – Biogas is beneficially reused to generate heat for the digesters and building heating via boilers. If Loudoun Water continues with digestion only and does not implement sludge pretreatment, and a thermal dryer is implemented, consideration should be given to using biogas to fuel the dryer. Using biogas for electric energy generation, via a combined heat and power (CHP) system or for renewable natural gas for vehicle fueling, should be considered when biogas production increases, or energy costs increase and/or the development of a strong and stable renewable energy credit (REC) market. Renewable energy projects, (e.g. solar) and energy recovery projects, such as wastewater heat recovery, will be implemented when they yield an economic benefit.
Significance of Work
This work documents a practical approach to developing flexible implementation strategies for an evolving future that can be used and adapted by other organizations. The strategies include trigger-based logic for decision making. Modular project components are included in the implementation plans to allow for “plug and play” of project components to adapt to the needs of the utility. Concepts reviewed in this work will allow utility managers to see how cutting edge innovations can be included in practical implementation plans that limit risk.
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