Organic matter release from primary sludge by mechanical cutting

Abstract

Surplus sludge disintegration to produce soluble organic matter for biological nutrient removal have been widely studied, however, the performance of mechanical disintegration of primary sludge is still unclear. A new mechanical cutting (MC) approach was proposed to disintegrate primary sludge in this study, the production and bioavailability of the soluble chemical oxygen demand (SCOD) was analyzed and the mechanism of organic matter release from primary sludge was investigated. With the mechanical cutting speed of 35,000 rpm, SCOD production increased with the increase of mechanical cutting time. When mechanical cutting for 8 min, the yield of organic matter reached the maximum, SCOD concentration and sludge disintegration degree (DD) were 1604 mg/L and 6.4 %, respectively. 32.3 % and 23.5 % of the SCOD was readily biodegradable organic matter (SS) and slowly biodegradable organic matter (XS). The denitrification rate of activated sludge was 2.23 mgNO3−-N/(gMLSS·h) with the organic matter released from primary sludge as carbon source, which was basically consistent with glucose. Mechanical cutting, centrifugation and pyrolysis were the main mechanisms for sludge disintegration and organic matter release, and pyrolysis played a major role.