Literature Review on Effect of Sludge Age on Microbial Community Structure in HMBR Min Li, Weiyuan Cao, Zhiheng Zhang, Guosen Peng, Zhixiang Hu, Guozhi Zhou and Kun Dong E3S Web of Conf., 406 (2023) 01023 Published online: 31 July 2023 DOI: 10.1051/e3sconf/202340601023