Pyrolysis characteristics of anaerobic digestate from kitchen waste and availability of Phosphorus in pyrochar

Pyrolysis of digestate from anaerobic digestion of kitchen waste yielded combustible gas and liquid with biochar as solid product. In this study, the pyrolysis characterization of the digestate and the P availability of the obtained pyrochar were discussed. Thermogravimetry (TG) analysis showed that 15.56 % of the weight loss occurred from 600 °C to 750 °C due to CaCO3 decomposition. When the final temperature increased from 500 °C to 700 °C, the HHV of pyrogas was slightly affected elevated from 17.20 MJ/Nm3 to 18.12 MJ/Nm3, while the relative content of polycyclic aromatic hydrocarbons (PAHs) in the liquid raised from 1.36 % to 6.28 %. SMT analysis showed that phosphorus in the pyrochar was fully converted to apatite phosphorus (AP) due to an excessive Ca content. Neutral ammonia citrate (NAC) extraction indicated that the availability of P in pyrochar was significantly decreased from 7.97 mg/g at 500 °C to 2.29 mg/g at 700 °C. Overall, the results showed that pyrolysis at 500 °C was suitable to obtain high-quality fuel and pyrochar with high P availability.