Enhancing Sewage Sludge Dewaterability by a Skeleton Builder: Biochar Produced from Sludge Cake Conditioned with Rice Husk Flour and FeCl3

Abstract

Biochar produced from sludge cake conditioned with rice husk flour and FeCl3 (biochar-conditioned) was used to enhance sewage sludge dewaterability. The pyrolysis temperature and dosage of biochar-conditioned were optimized, and the effect of biochar produced from raw sludge cake (biochar-raw) and biochar-conditioned on the sewage sludge dewaterability was compared. Moreover, the mechanisms of biochar-conditioned improving sludge dewaterability as a skeleton builder were analyzed. The optimal pyrolysis temperature of biochar-conditioned was 400 °C. The biochar-conditioned contained the sludge-based biochar with a high content of iron and rice husk-based biochar. Compared with biochar-raw, biochar-conditioned prepared at 400 °C was more effective at enhancing the sludge dewaterability, and the optimal biochar-conditioned dosage was 70% dry sludge (DS). Compared with adding FeCl3 alone, the sludge specific resistance to filtration decreased by 63.9%, the net sludge solids yield increased by 39.2%, and the net percentage sludge water removal increased to 98.36%. Large cracks made the sludge cakes permeable, so that more sludge moisture was filtered from the sludge cake. In addition, adding biochar-conditioned reduced the turbidity and SCOD of sludge filtrate and adjusted the sludge pH to neutral. Using biochar-conditioned to condition the sewage sludge as a skeleton builder is promising.