Proposed new facility at the Piscataway Wastewater Treatment Plant in Southern Prince George’s County that will convert biosolids from several WSSC wastewater treatment plants (Seneca, Damascus, Parkway, and Piscataway) into electricity. Proposed digestion and cogeneration improvements at the Piscataway wastewater treatment plant will reduce energy use, carbon footprint, and cost.
Anaerobic Digestion is the natural decomposition of organic materials by microbes that thrive in an oxygen free environment (An–Aerobic = “Without-Oxygen”).
Cogeneration is the simultaneous generation of electricity and heat that is normally discarded during electrical generation. Cogeneration is a much more efficient form of electric generation because no heat is wasted, as in conventional power plants.
WSSC’s Seneca, Piscataway, Damascus, and Parkway Advanced Wastewater Treatment Plants (AWWTPs) currently produce approximately 70,000 tons of biosolids per year. Biosolids are AWWTP sludge that has been treated to remove odors and disease-causing bacteria and allow beneficial reuse, typically as a soil fertilizer.
WSSC is considering anaerobic digestion with cogeneration as an alternative to the currently used chemical intensive lime stabilization process to treat the sludge. Anaerobic digestion is a biological process that converts a portion of the waste sludge to methane gas. This methane is in turn used to power clean-burning engines, producing electricity and heat needed for the digestion process.
The overall project is estimated to cost between $107 and $117 million. The baseline cost of existing lime stabilization plant upgrades that would have been necessary without the AD/ CHP project would have cost $50 million, making the net cost $57-$67 million. If WSSC can obtain public or private funding for the facility, the cost will be even less.
So far, WSSC has received $570,900 in federal funding. This provided for the feasibility study/conceptual design to determine the economic, environmental, and financial viability. It allowed WSSC to investigate potential anaerobicdigestion (AD)/combined heat and power (CHP) technology alternatives to optimize gas and electricity production and residual solids volume reduction, and recommend conceptual design/process for commercial application at each AWWTP.
The study/conceptual design phase was completed in December 2011. The results of the study were favorable and capital funding has been made available. Based on the approval of both County Councils WSSC is expected to proceed with the detailed engineering and construction of a commercial project.