Calcium-Loaded Municipal Sludge-Biochar as an Efficient and Stable Catalyst for Biodiesel Production from Vegetable Oil - Wang, Yazhuo; Li, Denian; Zhao, Dandan; Fan, Yukun; Bi, Jingwang; Shan, Rui; Yang, Jizhang; Luo, Bo; Yuan, Haoran; Ling, Xiang; Huhe, Taoli; Chen, Yong (ACS omega, 2020)