Effects of additives on combination of biodrying and pyrolysis: Greenhouse gas emissions reduction and apatite phosphorous improvement

Low-carbon sludge dewatering and efficient pyrolysis are crucial for the biomass industry's green development and solid waste resource utilization. This study investigated the combined effects of calcium oxide (CaO) and magnesium chloride (MgCl 2 ) addition during sludge biodrying, focusing on drying efficiency enhancement and greenhouse gas (GHG) emissions reduction, and further evaluated the following pyrolysis behavior of dried material. The combined addition of CaO and MgCl 2 created a thermophilic and alkaliphilic environment, consequently increasing the cumulative temperature by up to 69.50% compared to the control group, contributing to a further reduction of 8.11% in the final moisture content. Notably, CaO-MgCl 2 addition (BCM) improved the stability of key microbial phyla, resulting in the highest CO 2 emission reduction of 64.72%. The addition of CaO reduced the abundance of phosphorus-solubilizing microorganisms, and promoted the binding of calcium ions with phosphorus, enhancing the apatite phosphorous (AP) content in the dried material. Compared to the control group without additives (CK), BCM resulted in an 18.13% higher AP content in the dried material on day 11. This study provides novel insights into the synergistic effect achievable through additive introduction on high-efficiency sludge drying, GHG emissions reduction, and the high-AP biochar produced from the combination of biodrying and pyrolysis process.