Transforming anaerobically digested sludge into high-quality biosolids with an integrated physiochemical approach

Abstract

This study aims to propose an optimum integrated strategy for recovery and carbon sink by simultaneously considering low-valued recyclables recycling and non-recyclables reduction in anaerobically digested (AD) sludge management. This is achieved based on the scienctific finding in this study that three rounds of acid-elutriation of the AD sludge (pH ≤ 2) effectively reduced the water content of the sludge filtration cake from 96.3 ± 0.8 to 73.6 ± 0.6 wt%, indicating an 86% reduction of sludge volume. The acid-elutriation also improved the stabilization of AD sludge in terms of specific oxygen uptake rate and pathogen level, which meets the criteria of Class-A Biosolids (United States Environment Protection Agency). The quality of dewatered sludge was enhanced with the reduction of >80% metals (including toxic B, Cr, Mn, Ni, Pb, and Zn). Fundamental investigations in this study illustrated a new mechanism underlying the observed substantial dewaterability improvements, i.e. acid-elutriation removes hydrophilic organic matter and leads to decreased repulsive force from hydration interaction energy. This novel mechanism suggests potential opportunities of combining other treatment technologies with elutriation, to achieve enhanced dewatering performance.