Abstract:Activated sludge is the key functional element of biological wastewater treatment plants which employ an activated sludge process. This review enhances our knowledge about activated sludge microbial community and the development of its research method. Traditional cultivation-based studies could detect only 1％ to 15％ of microorganisms in activated sludge, therefore causing heavily biased shifts in community composition. With the emergence of a variety of cultivation-independent molecular methods, mainly based on 16S rRNA sequences, from the 1980s to the present, the biodiversity and complexity of activated sludge microbial communities were revealed at astonishing speed, and correspondingly numerous key microorganisms in activated sludge which were not detected by traditional cultivation methods, were disclosed by culture-independent techniques. Recently, many modern cultivation procedures, based on simulation of the environment conditions that the samples existed in, were developed and have successfully cultured some previously uncultivable microorganisms, offering the possibility of further exploring the physical characteristics and functional mechanisms of these newly recognized microorganisms. These advances undoubtedly promote our knowledge about activated sludge microbial communities to a higher level. This review introduces a series of methods about activated sludge microbial community research，including traditional cultivation-based methods, microbial biomarkers, molecular biological technology and modern culture approaches, especially focusing on a summarization of molecular biological technology, such as PCR-DGGE,FISH,FCM, and its application for research on the activated sludge bacterial community.