Effect of operating temperature on the efficiency of ultra-short-sludge retention time activated sludge systems

There are abundant recyclable carbon, nitrogen, and phosphorus resources in wastewater and their efficient recovery is a heavily studied topic at present. As an effective means of carbon and phosphorus recovery, the ultra-short-sludge retention time (SRT) activated sludge (USSAS) system has increasingly attracted the attention of researchers. In this study, the capture efficiency and mechanism of carbon/phosphorus, and the microbial characteristics of the USSAS system, were studied at different temperatures (12, 18, 24, and 30 °C) and a 3-day SRT. The results showed that temperature had little effect on the carbon capture efficiency but had a considerable impact on the carbon capture mode. Increasing temperature decreased the EPS content and increased the biological metabolic activity, then decreasing adsorption but increasing the biotransformation effect. There was a negative correlation between temperature and phosphorus capture efficiency. As the temperature increased, the biological phosphorus removal effect decreased, but the adsorptive phosphorus removal effect gradually increased. With decreasing temperatures, the mixed liquid volatile suspended solid (MLVSS)/mixed liquid suspended solid (MLSS) value increased, but there was a risk of sludge bulking. Kinetic parameters confirmed microbial energy storage under lower temperature conditions and high biological activity under higher temperature conditions.