Deep sludge dewatering enhanced by biochar skeletons from different sources: performance comparison and mechanistic insights

Abstract

To improve the performance of sludge pressure filtration and achieve deep dewatering, this study compared the effects of three biochar skeleton materials derived from different sources—anaerobic sludge biochar, surplus sludge biochar, and rice husk biochar—on sludge conditioning. The enhancement mechanisms were systematically investigated by analyzing changes in particle size distribution, zeta potential, and the contents of polysaccharides and proteins in extracellular polymeric substances (EPS). Experimental results showed that the addition of biochar skeletons significantly improved sludge dewatering efficiency, with anaerobic sludge biochar reducing the sludge cake moisture content to 63.98% ± 0.54% at a dosage of 50% (on a dry sludge basis). Mechanism analysis indicated that biochar skeletons neutralized surface charges, increased particle size, and adsorbed hydrophilic EPS components to promote floc formation. These effects further facilitated the construction of mechanically stable skeleton structures and stratified drainage channels, which helped maintain sludge cake permeability under high pressure, enhance filtration performance, and ultimately achieve deep dewatering. This study provides important theoretical foundations and engineering support for the development of novel sludge conditioners and the optimization of deep dewatering processes.