An Evaluation of Dewatered Sludge Percent Solids at District of Columbia Water and Sewer Authority (DCWASA)

Janpengpen, A.1, Baecher, G.1, Peot, C.2, Ramirez, M.2, 1University of  Maryland, USA, 2District of Columbia Water and Sewer Authority, USA


The District of Columbia Water and Sewer Authority’s (DCWASA) operates an advanced 1,400,000
m3/d wastewater treatment plant (WWTP) at Blue Plain in Washington, DC. This facility uses high
speed centrifuges to separate water from solids to generate high cake solids. DCWASA post limes
these cake solids and applies biosolids to over 81 km3 of agricultural land.

The study correlates the dewatered sludge percent solids to various operational parameters
throughout the wastewater treatment process and employs statistical modelling to explain and
identify the relationship of those parameters. The model found that among 24 process parameters,
process effluent temperature, blend ratio, and settled sludge volume are the most significant
parameters that correlate and contribute to the dewatered sludge percent solids. In addition, percent
solids of gravity thickening and the secondary west blanket depth also have a considerable influence
percent cake solids. This study provides the information to DCWASA for the cost effective
management of solids and should decrease the total tons of biosolids generates and the overall cost
for truck removal and land application.

Biosolids, dewatering process, dewatered sludge, percent solids, blend ratio.

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