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.