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

•Aqueous phase (AP) from hydrothermal carbonization (HTC) was used in composting.•APs from rice husk (RH) and/or sewage sludge (SS) served as moisture regulators.•AP-RH-SS reduced cumulative NH3 emissions by > 41.74%.•AP-RH-SS and AP-SS increased the total nitrogen content by > 20%.•AP-RH-SS and AP-SS significantly increased the humification in the composting.