Abstract: Abstract: A novel wastewater treatment process in our previous research can perform denitrifying simultaneous nitrogen and phosphorus removal and phosphorus recovery via induced crystallization (thereafter called BNR-IC process). Generally, removal efficiencies of contaminants including carbon, nitrogen and phosphorus through wastewater biological treatment process may be attributed to characteristics of predominant microorganisms in activated sludge. In this BNR-IC process, microorganism enriched in the anoxic tank is one of key factors influencing the removal of carbon, nitrogen and phosphorus from wastewater. The aim of this study was to investigate the characteristics of activated sludge from the anoxic tank in the BNR-IC process, including the performances of anaerobic phosphorus release, aerobic or anoxic phosphorus uptake, and the characteristics of microorganisms responsible for denitrifying simultaneous nitrogen and phosphorus removal. In this study, two batch tests were conducted to analyze the capacity of release phosphorus in anaerobic condition and uptake phosphorus under aerobic or anoxic conditions. Fluorescence in situ hybridization (FISH), scanning electron micrograph (SEM) and chemical staining were also utilized to investigate the amount of polyphosphate-accumulating organisms (PAO) in activated sludge and its morphologies. FISH results showed that the ratio of polyphosphate-accumulating organisms (PAO) to total bacteria was 69.7% higher than that of single-sludge system. A variety of bacilli were found in the activated sludge samples by SEM. The amount of phosphorus taken up per MLSS, i.e. PO43--P/MLSS, in anaerobic-aerobic environment was 22.84 mg/g. It was 18.60 mg/g in anaerobic-anoxic condition, the ratio of DPAO to PAO in anoxic tank was 81.44%. The results also indicated that DPAO can be effectively enriched in a long-term operation under anaerobic-anoxic environment. PAO can be divided into two types: one uses nitrate or oxygen as an electron acceptor, and the other can only use oxygen as the electron acceptor. Moreover, better understanding of the biochemical processes in wastewater biological treatment process can be obtained by monitoring the value of pH or ORP, providing the benefit for controlling the process. These results showed that the combination of chemical analysis with microorganism investigation may serves as a new indicator for stable operation or application of the novel BNR-IC process. It may become a new trend in the future development of wastewater biological treatment and phosphorus recovery process.