DC WASA Biosolids Management Program

Treating Wastewater in the 21st Century

Owned and operated by Washington, DC’s Water and Sewer Authority (DC WASA), the Blue Plains Advanced Wastewater Treatment Plant (AWTP) treats wastewater from almost 4 million residents in Washington, DC, and adjacent counties in Maryland and Virginia. Considered to be the world’s largest AWTP, Blue Plains has an average capacity of 370 million gallons/day and can treat 400 dry tons/day of primary, waste-activated, and nitrification sludge.

Parsons has worked with DC WASA for more than 20 years, and in the late 1990s we designed the lime biosolids stabilization system used at the Blue Plains AWTP. In this process, wastewater is converted into stabilized biosolids—an organic, renewable resource—and then applied to the soil as an agricultural amendment. DC WASA has received several awards from the U.S. Environmental Protection Agency for the existing lime system and its beneficial-use program for the biosolids product.

Parsons is working with the DC WASA staff to implement a new system at the Blue Plains AWTP in order to meet the demands of the 21st century. In one of the nation’s most ambitious and innovative biosolids management programs, the new and upgraded process will replace lime stabilization with thermal hydrolysis and mesophilic anaerobic digestion. As part of a team with DC WASA and other consultants, we are performing planning, feasibility studies, technology evaluations, process modeling, conceptual designs, cost evaluations, design management, and program management.

Environmental Advantages

After the new facilities are completed in 2014, they will provide the following major environmental advantages:

• Clean-burning digester gas (140 mm Btu/day) for heat and power.
• Reduced air emissions onsite and from commercial power sources.
• Electrical power (13 MW) generated onsite that closely matches critical process requirements.
• Nearly 50% reduction in biosolids volume, thereby saving 1,275 gallons/day in diesel fuel (because of a reduced need for hauling).
• Lime stabilization for peaks only, thereby reducing lime use by 40 tons/day (lime requires high energy to produce).
• Class A biosolids with reduced risks and expanded beneficial uses (when compared to the Class B biosolids now produced).

Thermal Hydrolysis and Mesophilic Anaerobic Digestion

From 2006 through 2008, Parsons was a key member of the Blue Ribbon Panel that worked with DC WASA to consider 15 alternatives and then select a sustainable, cost-effective technology that combines thermal hydrolysis and anaerobic digestion.

During thermal hydrolysis, biosolids are treated with pressurized steam that destroys pathogens and greatly enhances digestion. Thermal hydrolysis itself is an innovative technology:

• The process enables the subsequent step (i.e., digestion) to take place in tanks that are one-half the size than would otherwise have been required, thereby achieving a savings on capital costs.
• It creates more digester gas than conventional technologies.
• It generates superior Class A biosolids that have minimal health and environmental risks.

The four anaerobic digesters selected for this program will be among the largest in the world, each having a capacity of 3.85 million gallons.

Energy Production and Heat Recovery

Thermal hydrolysis and anaerobic digestion produce digester gas, which is a clean-burning power source. This renewable energy will provide 13 MW of electricity—one-third of the power needed to operate the Blue Plains facility and enough to supply emergency power requirements during power outages or energy disruptions. DC WASA’s new Renewable Energy and Emissions Reduction Facility (REERF) is a combined heat and power (CHP) system that burns digester gas in gas turbines (GTs), followed by heat recovery steam generators (HRSGs), followed by steam turbines (STs). A steam boiler will ensure adequate steam production. Steam will heat the thermal hydrolysis/anaerobic digestion process, and it will replace some of the existing natural gas heaters at the Blue Plains AWTP.

Program Innovations

Parsons developed a financial analysis model that became an important decision-making tool in evaluating the 15 alternatives. The unique, sophisticated model incorporates key process and financial aspects into graphic illustrations showing the cost-effectiveness of alternatives. It predicts the breakeven points and payback time frames, and it considers financing options. Parsons’ model led to the development of another program innovation—creative debt financing.

Because these new biosolids facilities will deliver major savings (when compared to existing operations), deferring debt repayment until after construction completion offers great advantages:

• The generation and use of green power will result in lower facility energy costs.
• Greatly reduced trucking operations will lower fuel consumption, pollution, and noise.
• The reduced volume and Class A designation of the final biosolids product will minimize disposal costs.

The program is being implemented by a combination of traditional design-bid-build, design-build, and design-build-operate contracts. This array of project delivery methods optimizes the advantages of various program elements.

Parsons developed the biosolids process model for this program that integrates various biosolids characteristics, quantity variations, peak loadings, and process performances. The model enables careful consideration of diverse process options while still in the planning phase.

Sustainable Solutions for a Growing Population

DC WASA’s biosolids management program demonstrates that sustainable solutions benefit ratepayers as well as the environment:

• The generation and use of green power will result in lower facility energy costs.
• Greatly reduced trucking operations will lower fuel consumption, pollution, and noise.
• The reduced volume and Class A designation of the final biosolids product will minimize disposal costs.

Parsons is helping DC WASA meet its vision of creating a self-sustaining, world-class biosolids management program for the Blue Plains AWTP. Parsons is a leading source of wastewater engineering and construction solutions—providing the most technically feasible and economically practical results for our customers throughout the world.