High-pressure jet device for activated sludge reduction: Feasibility of sludge solubilization

• A novel sludge reduction technology (HPJD), based on a high pressure pump, was developed.
• The operational condition was optimized to maximize sludge reduction efficiency.
• HPJD damaged microorganism cells in activated sludge.
• The organic compounds dissolved from damaged microorganisms were biodegradable.
• HPJD was found as a high-throughput and cost-effective technology for activated sludge reduction.

The objective of this study was to investigate the feasibility of a high-pressure jet device (HPJD) as an alternative technology to reduce the amount of excess activated sludge in a low-cost and simple manner. The device received concentrated activated sludge from two different ports: a horizontal port that transferred activated sludge with a jet flow via a nozzle and a side port that aspirated activated sludge with air. An investigation into the manner in which activated sludge was supplied indicated that the activated sludge conveyed by horizontal jet flow with aspiration from the elevated side port provided the highest degree of activated sludge reduction in the mixed liquor suspended solid (MLSS). The degree of reduction was 12.2% and the viable microorganisms decreased by 42.8%. The injection ratio R was defined as the amount of activated sludge from the side port to that of the nozzle. We found an optimum value of three with a MLSS reduction of 40%. The eluted constituents from the damaged cells or the intracellular compounds were biodegraded by the intact activated sludge. Estimation on cost and performance for activated sludge reduction, based on the energy and MLSS reduction, showed that the HPJD is twice as cost-effective as conventional technologies and that the throughput is 3.2–7.2 times as high as a high pressure homogenization device.

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