Heterogeneity of biochar amendment to improve the carbon and nitrogen sequestration through reduce the greenhouse gases emissions during sewage sludge composting

•Biochar additions increased the dehydrogenase activity during composting.•Biochar have a potential impact on reduction of N losses and gaseous emissions.•Biochar amendments shorten the thermophilic phase period.•Biochar additions increased CO2 emission and reduce the ammonia losses.•Biochar additions have significant correlation with carbon and nitrogen losses.

This study was performed to investigate the effects of biochar as an amendment to a gaseous emissions and sewage sludge (SS) composting dynamics. Six dosage of biochar [low dosage of biochar (LDB) - 2%, 4% and 6%; and higher dosage of biochar (HDB) - 8%, 12% and 18%] were amended to a mixture of SS and wheat straw (4:1 ratio on dry weight basis) and compared to control or without additive. The HDB significantly reduced CH4, N2O and NH3 emission by 92.85-95.34%, 95.14-97.30% and 58.03-65.17%, but not the CO2 emission. Meanwhile, humification results indicated that humic and fulvic acid 35-42% and 24-28% higher in the HDB amended treatments than those in the LDB and control treatments. The HDB significantly decreased total nitrogen losses and greenhouse gas emission, while LDB had significantly (p < 0.001) higher CH4 and N2O emissions. Due to effective performance of HDB, the 12% biochar was recommended to be used in SS composting practice.

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