EchoWater Facility Biosolids Emergency and Planning

Presentation Description: In April 2021, the EchoWater Resource Recovery Facility (Sacramento, CA) completed its conversion from a high-purity oxygen activated sludge process to a biological nutrient removal (BNR) process to meet revised ammonia effluent limits. Waste activated sludge from the BNR process is sent to the solids handling process which consists of thickening, anaerobic digestion, solids storage basins (SSBs), and onsite dedicated land disposal. During the BNR design effort, the solids handling process was left largely unchanged as major changes in solids loading were not expected. While that expectation has proven true, the digested sludge characteristics have changed dramatically to be less biodegradable and less settleable. These changes have had unexpected and near catastrophic consequences for the SSBs and the treatment processes as a whole.

By February 2023, excess solids in the SSBs began returning to the headworks via supernatant weirs, increasing plant loading to levels not anticipated until 2048. The elevated return load drove additional biomass growth in the BNR process, which further stressed the solids handling process creating an unsustainable positive feedback loop. Solids accumulated throughout the secondary process, Operations staff were unable to control rising sludge blankets, and hydraulic limitations prevented further wasting from the BNR facility. By June 2023, the EchoWater Facility was inundated with SSB biosolids. Secondary clarifiers were approximately three weeks from sending solids over their weirs, which would have blinded tertiary filters and risked an effluent violation.

EchoWater staff responded to the emergency by hiring a contractor to reduce the amount of solids stored in the SSBs, provided winter contingencies, evaluated long-term solutions for biosolids management, and began working on a $450 million capital improvement project. Improvement includes new thickening/dewatering and storage facilities for onsite biosolids disposal. This is a case study that offers insights into how a major treatment process upgrade can impact all downstream processes and provides a project status update on the long term solution to those impacts.