Paradigm Shift to Water Resource Recovery Facilities:
Impacts to and Opportunities at WSSC
The water/wastewater industry and Utilities of the Future are moving toward more Resource Recovery. Historically, the wastewater industry has focused on protecting water quality and meeting very low nutrient discharge limits through relatively high energy treatment technologies and chemical use (increased pumping, aeration energy, and chemicals for nitrogen and phosphorus removal). Currently, WSSC Water’s five major water resource recovery facilities (WRRF) achieve the following:
- Meet among the lowest nitrogen and phosphorus limits in the United States using advanced treatment and enhanced nutrient removal;
- Recover water from wastewater;
- Return clean water to the environment;
- Reuse a small portion of the water on-site for plant purposes;
- Beneficially reuse biosolids as a Class B fertilizer; and
- Use renewable energy (wind and solar) to provide a significant portion of power to the facilities.
The industry now has a number of innovative strategies and technologies to achieve more resource recovery, meet low nutrient limits that protect the environment, and substantially reduce energy and chemical use. Some of these technologies and new ways of operating are currently being tested and/or used at our WRRFs. In addition, a design-build project is currently underway to construct a new Bio-Energy facility at the Piscataway WRRF, which will recover more resources from the wastewater in the form of heat and renewable natural gas. This facility will be substantially completed by 2024.
To continue to achieve more resource recovery, WSSC Water is exploring the following opportunities:
- Optimize energy use – Continue to look for ways to optimize treatment processes and identify energy improvements. Energy audits have been conducted for each of the WRRFs, and areas of potential improvement have been identified. Multiple energy improvement projects have been initiated.
- Consider alternative carbon sources to enhance denitrification – Many of WSSC Water’s WRRFs have switched from methanol to more cost-effective carbon sources that not only save money but also still achieve excellent nitrogen removal performance. Reclaimed waste products as a carbon source for denitrification will also continue to be considered. Use of reclaimed products is a better use of resources and reduces greenhouse gas impacts.
- Evaluate primary treatment and/or carbon diversion for applicable plants – Carbon diversion prior to the biological treatment process reduces aeration energy demands, substantially enhances biogas production (and renewable energy credits), and reduces residual solids to be land applied when used in conjunction with anaerobic digestion. Tradeoffs include increased chemical doses and potential need for capital improvements. Additional evaluations are underway to determine if more carbon diversion makes sense for WSSC Water given the operating cost savings and capital costs.
- Add enhanced biological phosphorus removal (EBPR) where possible – This innovative treatment strategy reduces alum chemical and hauling costs. It also allows WSSC Water to potentially recover phosphorus from biosolids in the future. Another potential benefit is that it may increase biogas production at the Bio-Energy facility based on preliminary tests. Pilot testing and more detailed evaluations are underway. The inline fermentation option was tested at Seneca and Western Branch, and the success of that approach led to the sidestream EBPR process that is currently being piloted at the Parkway WRRF.
- If EBPR is implemented, evaluate phosphorus recovery – Phosphorus is a critical and limited resource, and can be recovered as a marketable product from the biosolids to generate revenue. Extracting phosphorus from the biosolids also reduces the content in the biosolids, potentially alleviating land application limitations.
- Evaluate co-digestion of food waste and other high strength wastes – Co-digestion at the Piscataway Bio-Energy facility (addition of fats, oils, greases, food wastes, and other high strength wastes) can improve the volatile solids reduction, biogas production, and energy production substantially thereby offsetting costs and/or generating revenue. Impacts to the nitrogen and phosphorus performance at the Piscataway WRRF would also have to be evaluated.
- Consider mainstream shortcut nitrogen removal and/or other efficient oxygen transfer processes – More efficient nitrogen removal can reduce aeration energy requirements, supplemental carbon chemical costs, and solids hauling costs. In addition, the chemical costs associated with carbon diversion can be offset with this approach. Research into innovative nitrogen removal is underway at WSSC Water’s WRRFs and by other utilities.
- Continue to expand use of renewable energy sources (e.g., wind, solar, co-digestion, microhydro, thermal energy recovery) – The Patuxent Water Filtration Plant uses hydraulic turbines to pump water from the reservoir to the plant to generate energy when sufficient water is present in the reservoir. Several years ago, WSSC Water established solar sites at both the Seneca and Western Branch WRRFs, and the Piscataway Bio-Energy facility will generate renewable energy once the facility is online. WSSC Water is evaluating hydropower, wastewater heat recovery, and other ways to expand renewable energy.
- Look to expand water reuse opportunities – WSSC Water continues to look for industries or groups in the area that may be interested in non-potable water reuse. This region is currently not experiencing a water shortage, which decreases the demand for water reuse at this time.
- Evaluate additional Biosolids-to-Energy technologies after the Bio-Energy facility is in operation – Although WSSC Water biosolids from the WRRFs will be upgraded to Class A exceptional quality biosolids and reduced in half after anaerobic digestion, WSSC Water will still need to land apply or find other ways to reuse the remaining biosolids. Evaluations are underway regarding additional cost-effective ways to upgrade/treat the biosolids to produce a desirable year-round biosolids product portfolio.
WSSC Water continues to be a Utility of the Future. The organization is evaluating and implementing strategies to achieve more resource recovery, all while protecting the environment, reducing operating costs, improving efficiency, developing new pathways for revenue, and increasing sustainability of operations and infrastructure.