Usage of pumice as bulking agent in sewage sludge composting

•Water absorption characteristics of pumice were studied.•Pumice can hold water during composting.•Reused pumice promoted degradation of organic matter and reduced nitrogen loss.•Sucrose-decorated pumice was used to reduce nitrogen loss.

In this study, the impacts of reused and sucrose-decorated pumice as bulking agents on the composting of sewage sludge were evaluated in the lab-scale reactor. The variations of temperature, pH, NH3 and CO2 emission rate, moisture content (MC), volatile solid, dissolved organic carbon, C/N and the water absorption characteristics of pumice were detected during the 25 days composting. The MC of pumice achieved 65.23% of the 24 h water absorptivity within the first 2 h at the mass ratio of 0.6:1 (pumice:sewage sludge). Reused pumice increased 23.68% of CO2 production and reduced 21.25% of NH3 emission. The sucrose-decorated pumice reduced 43.37% of nitrogen loss. These results suggested that adding pumice and sucrose-decorated pumice in sludge composting matrix could not only adjust the MC of materials, but also improve the degradation of organic matters and reduce nitrogen loss.