Improvement of sludge dewaterability by ammonium sulfate and the potential reuse of sludge as nitrogen fertilizer.

Abstract A novel method to enhance sludge dewaterability with ammonium sulfate ((NH4)2SO4) was proposed, and the potential reuse of dewatered sludge cake and filtrate as nitrogen fertilizers was evaluated. Compared with raw sludge, 87.91% reduction of capillary suction time (CST) and 88.02% reduction of specific resistance to filtration (SRF) after adding 80% (m/m) (NH4)2SO4 were achieved, with 38.49% of protein precipitated simultaneously. The (NH4)2SO4 dose destroyed cell membrane, resulting in the release of intracellular water by converting bound water into free water, thus enhancing sludge dewaterability. In the solid phase, the content of protein-N increased, and larger protein aggregates were formed. The (NH4)2SO4 dose destroyed the hydration shell, making proteins to exhibit hydrophobic interactions, and to be aggregated, and precipitated from the liquid phase. When incubated Pennisetum alopecuroides L. with the dewatered sludge cake and filtrate after dewatering and conditioning with (NH4)2SO4, the germination rate of grass seed and shoot lengths both increased while compared with those incubated with dewatered sludge cake and filtrate of the raw sludge. This study might provide insights into sustainable sludge treatment by integrating sludge dewatering and the potential reuse of dewatered sludge cake and filtrate as nitrogen fertilizer via treatment with (NH4)2SO4.