Influence of pyrolysis temperature on composted sewage sludge biochar priming effect in a loamy soil

•Biochar reduced the soil CO2 emissions between 11% and 32%.•CO2 evolution after biochar addition is well fit to a dual first-order kinetic model.•Simulation of CO2 emissions showed a reduction over 932 kg CO2 ha−1 after 10 yr.

Biochar is a carbon-rich solid product obtained by the pyrolysis of organic materials. The carbon stability of biochar allows that it can be applied to soil for long-term carbon storage. This carbon stability is greatly influenced by the pyrolysis temperature and the raw material used for biochar production. The aim of the present work is to study the soil carbon sequestration after the application of biochar from sewage sludge (SL) pyrolysis at two different temperatures (400 and 600 °C). For this purpose, soil CO2 emissions were measured for 80 d in an incubation experiment after soil amendment with the SL and each biochar at a dosage of 8 wt%. Biochar reduced the CO2 emissions during incubation between 11% and 32% relative to the SL treatment. The CO2 data were fit to a dual exponential model, and the CO2 emissions were simulated at different times (1, 5 and 10 yr). Additionally, the kinetics of the CO2 evolution from SL, two biochar samples, soil and amended soil were well fit to a dual first-order kinetic model with correlation coefficients greater than 0.93. The simulation of CO2 emissions from the soil by applying the proposed double first-order kinetic model (kg CO2C ha−1) showed a reduction of CO2 emissions between 301 and 932 kg CO2C ha−1with respect to the direct application of raw sewage sludge after 10 yr.