Effect of Microsludge on Anaerobic Digester Performance and Residuals Dewatering at La County’s JWPCP

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MicroSludge™ is a patented chemical and pressure pretreatment process that liquefies waste activated sludge (WAS) to increase both the rate and extent that it is degraded in a conventional mesophilic anaerobic digester (CMAD). The process uses chemical pretreatment to weaken cell membranes and a high-pressure homogenizer, or “cell
disrupter”, to provide an enormous and sudden pressure change to burst the cells. The resulting liquefied WAS is more readily converted to biogas in a CMAD. Following the demonstration of the first full-scale MicroSludge unit near Vancouver, Canada in 2004, the second full-scale unit was commissioned at the Los Angeles County Sanitation Districts’ Joint Water Pollution Control Plant (JWPCP) in October 2005. The JWPCP is located in Carson, California and treats 400 MGD of wastewater, serving a population of approximately 3.5 million. Additionally, the JWPCP also treats solids from the LACSD’s upstream water reclamation facilities for a solids loading population equivalent of approximately 5 million. Two 4,000 L/h cell disruption modules were continuously operated for 24 hours per day to process approximately 192 m3/day (50,000 GPD) of thickened WAS (TWAS) at a 5 to 6 percent total solids (TS) concentration. The processed TWAS was then co-digested with primary sludge (PS) in a 75:25 by volume (approximately 68:32 by mass) PS:TWAS mix at an HRT of approximately 19 days. The digester performance was compared with the performance of one of the other 23 CMAD digesters that was operated under similar conditions at the JWPCP, except that the TWAS feed was not pretreated.

This paper outlines the results obtained to date of the on-going testing program.

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