How additives steer sewage sludge hydrochar properties: Divergent pathways of MgO/CaO versus sawdust in carbon/nutrient fate and magnetism - Chen Zhang; Guo Chen; Qinghai Wang; Huafen Li; Yanan Wan; Guoxin Sun; Ke Wang; Tianshu Chu; Ruilun Zheng (Bioresource Technology, 2026)