Study on Sewage Sludge Drying System With Built-in Solar Drying Bed Zhipan Gu, Jichun Yang, Jing Liu, Leren Tao, Ye Zhang and Lihao Huang E3S Web Conf., 237 (2021) 01041 Published online: 09 February 2021 DOI: 10.1051/e3sconf/202123701041