The DC Water and Sewer Authority (DCWASA) is developing new plans and details for sludge and biosolids processing at the 1.4 million m³/day (370-mgd) Blue Plains Advanced Wastewater Treatment Plant in Washington DC. The program includes thermal hydrolysis of sludge followed by anaerobic digestion, and will include a major combined heat and power facility to provide electrical power for the treatment plant and steam for the thermal hydrolysis process. The resulting Class A biosolids cake product will meet all Exceptional Quality criteria and will have a much broader use than the current lime-stabilized Class B product. The quantity of product will be cut dramatically. The development of the biosolids program has included significant risk evaluation and cost assessment work. Various potential technical and procurement risks became apparent during program and project development. These included risks from increased solids production along with system performance risks, equipment procurements, and risks concerning final product quality. Methods to control the risks were identified, evaluated, and included in the program. In some cases, risk reduction caused potential cost increase, so that almost constant cost assessment has been required to minimize scope and cost pressures. Sustainability criteria for the program include major efforts to minimize power and energy use and to generate maximum renewable power from the digester gas. This work results in significant reduction in greenhouse gas emissions for DCWASA. Also, the program features will create maximum opportunities for long-term development of value-added biosolids products.
Cost Control and Risk Reduction – Precepts for Developing DCWASA’s Biosolids Program in the Age of Sustainability
Authors: Perry Schafer, Walt Bailey, Martin Sultan, Chris Peot, Sudhir Murthy, Phil Braswell and Alan Cooper