Sludge Reduction in a Full-scale Wastewater Treatment Plant Using Ultra-fine-and Micro-bubble Ozonation

Abstract

ABSTRACT Biological wastewater treatment plants (WWTPs) produce large amounts of excess sludge. One approach to reduce sludge is treatment with ozone, which promotes sludge disintegration and solubilization. Here we report the first application of ultra-fine- and micro-bubble (UFB/MB) ozonation to sludge reduction in a full-scale WWTP. UFB/MB ozonation using a spiral liquid-type UFB generator was applied to concentrated excess sludge in the storage tank instead of to return sludge. At an ozone dose of 15 mgO3 gSS–1, a 92% reduction in sludge accumulation rate was achieved during a 237-day ozonation period with ozonation relative to a 100-day no ozonation period without ozonation. This reduction was larger than expected, and was partly due to a 20–30% greater average concentration of suspended solids in the influent during the no ozonation period. Addition of UFB/MB ozonation to the existing activated sludge process did not reduce the water quality in the effluent. We can conclude that UFB/MB ozonation for concentrated excess sludge in the storage tank using a spiral liquid-type UFB generator remarkably reduced the ozone dose required to sludge reduction by more than half of the reported conventional ozonation (30–150 mgO3 gSS–1) without the negative impact on effluent water quality.