Biochar Prepared by Microwave-Assisted Co-Pyrolysis of Sewage Sludge and Cotton Stalk: A Potential Soil Conditioner

The reduction and safe disposal of sewage sludge remains an urgent problem worldwide. In this work, biochar prepared from co−pyrolysis of sewage sludge and cotton stalk at different mix ratios and different pyrolysis temperatures was prepared using a novel microwave-assisted auger reactor. The obtained biochar samples were mixed with selected soil samples at different mix ratios for a short−term plant−growing test to examine their abilities as a soil conditioner on nitrogen fixation and retention. The addition of biochar could increase the total nitrogen in the soil to 0.3951% compared to 0.0403% in the untreated soil, while the concentration of available nitrogen could be increased to 114.45 mg·kg −1 compared to 47.95 mg·kg −1 in the untreated soil. Moreover, the introduction of biochar to the soil also contributed to the growth of corn seedlings, which grew at a rate of 3.41 cm·d −1 compared to 3.03 cm·d −1 in untreated soil. The results show that the addition of biochar can enrich total soil nitrogen before and after incubation and promote the growth of corn seedlings, providing a potential route for the safe disposal and resource recovery of sewage sludge.