The DC Water and Sewer Authority (DC Water) is proceeding with implementation of its $470 million biosolids program which involves large-scale thermal hydrolysis of wastewater solids followed by anaerobic digestion to produce a high-quality Class A biosolids product. The facilities are all under construction at this point. Decisions on the specific technologies that are being used for solids dewatering were made during the detailed planning and pre-design work of the biosolids program development. The primary technology and related decisions are as follows: • Centrifuge technology was selected for pre-dewatering of mixed primary and waste-activated sludge material. This is the dewatering step prior to thermal hydrolysis. Minimal cake conveyance after this pre-dewatering step was also a critical factor in system development. • Belt filter press technology was selected for final dewatering of the Class A anaerobically digested solids. Product characteristics became a crucial issue for final dewatering decisions. Multiple factors were involved in making these and related decisions. Specific research and testing work, as well as overseas due diligence work at operating thermal hydrolysis and digestion plants was utilized to develop required information so that highly informed evaluations could be completed. The DC Water team anticipates that this extensive level of evaluation work completed will result in improved solids processing system operation when the facilities are brought on-line in 2014.
Decision Factors on Solids Dewatering Technologies for DC Water’s Biosolids Program
Authors: Perry Schafer, Salil Kharkar, Sudhir Murthy, Chris Peot, Diala Dandach, Sam Roberts, Phil Braswell