Effect of biochar amendment on greenhouse gas emission and bio-availability of heavy metals during sewage sludge co-composting

In the present study, we evaluated the feasibility of biochar amended with lime (B + L) to reduce the loss of ammonia, greenhouse gas (GHG) emissions and the bio-availability of heavy metals (HMs) during composting of dewatered fresh sewage sludge (DFSS) and to improve the end product quality. Biochar mixed with a low dosage of lime was supplemented at a 1:1 ratio into DFSS and wheat straw (dry weight basis), and compared with a lime only amendment and a control without any amendment. The CO2 emission profile clearly indicated that the B + L addition was effectively buffered a pH ∼8.0, and the B + L amendment experienced an enhanced the rate of decomposition compared to control and lime amended treatments. In aerobic co-composting, the B + L amendment effectively reduced the loss of ammonia, CH4, and N2O emission. B + L amended DFSS compost also showed significantly higher concentrations of humic-acid (17.23%) and fulvic-acid (3.79%) compounds, effectively reduced the bio-availability of HMs (34.81% Cu, 56.74% Zn, 87.96% Pb and 86.65% Ni) and improved compost maturity compared to control and lime amendments. Furthermore, the B + L amendment increased the adsorption of ammonium ions by reducing the ammonia loss and N2O emission, resulting in compost with higher nutrient concentrations. These results can be used to formulate the initial feedstock for industrial scale composting processes.