Effect of the aqueous phase from the hydrothermal carbonization of sewage sludge as a moisture regulator on nitrogen retention and humification during chicken manure composting

The hydrothermal carbonation (HTC) of sewage sludge (SS) produces a large amount of an aqueous phase (AP), which has become a bottleneck for the development of HTC. Herein, the effectiveness of the AP from HTC as a moisture regulator for composting was investigated in terms of nitrogen (N) retention and humification. The AP from the HTC of SS (AP-SS) and that from the co-HTC of rice husks and SS (AP-RH–SS) were considered. Experimental results showed that AP-RH–SS and AP-SS reduced the cumulative ammonia emissions from compost by 41.74% and 9.98%, respectively; reduced the N losses by 36.68% and 14.91%, respectively; and increased the total N concentrations by 28.17% and 21.08%, respectively, compared with those from control treatment. AP-RH–SS and AP-SS promoted the humification process and considerably increased the humic content, humification index, and germination index of the compost products. Moreover, AP-SS and AP-RH–SS promoted the degradation of aliphatic proteins and increased the amount of unsaturated and aromatic components during composting while decreasing the average molecular weight of the dissolved organic matter in the compost products. These findings provide new insights into the design and implementation of joint management strategies for the AP and composting.