Studies On Mechanism Of Biological Phosphorus Removal In Sequencing Batch Reactors Under Single-stage Oxic Condition

Phosphate (Pi) is important nutrition for biology, but excessive Pi supply to water will lead to ecosystem balance through a process known as eutrophication. Therefore, efficient and reliable Pi removal methods are very important to the increasingly stringent problem of eutrophication. Compared to chemical Pi removal, biological Pi removal has attracted more researchers'attention due to its lower operational cost and lower environmental impact.Although anaerobic/aerobic (A/O) process is widely applied in real wastewater treatment, the stability and reliability of the process can be still a problem. Even operated under seemingly favorable operational conditions, deterioration in performance and even failures of A/O systems have been widely reported in literatures due to external disturbances such as high rainfall, excessive nitrate loading to the anaerobic reactor, or nutrient limitation. Moreover, the strong dependence on volatile fatty acids (VFAs) of wastewater restricts its further application. When the VFAs concentrations of wastewater are low, periodic organic matter supplementation and/or chemical"polishing"may be required to attain compliance, as a result, the operational cost increased.Our recent study on possible alternatives to the conventional A/O process has demonstrated that it is possible to increase the level of Pi removal using glucose as the sole carbon source without anaerobic period, and defined this as single-stage oxic process. The phenomena may enrich the theory of biological Pi removal and form a potentially economical and simple strategy for the"one-step"removal of Pi and organic substrates from wastewater. However, the former investigation is just primary exploration, a series of key questions behind the phenomenon are not solved. Thus, to reveal the special mechanism of polyphosphate accumulation under single-stage oxic process, this problem conducts a series of application basic researches financially supported by the National Natural Science Foundation of China.The results showed that excess uptake by some organisms in activated sludge caused the abnormal phenomenon of phosphorus removal in sequencing batch reactor without anaerobic period, and this process could achieve biological phosphorus removal to a certain extent when respectively used peptone, acetate, ethanol and glucose as a sole carbon source. The bacterial community structure analysis showed that the systems had complexity and diversity of microbial ecology in the sludge samples, and indicated that high levels of Pi removal in systems were not achieved by the accepted PAO during steady operation period but most likely by Zooglea sp.. Also, metabolic pathways of Zooglea sp. were carried out to explain the key questions of inducing condition, inducing reason, mechanism of polyphosphate uptake and effect mechanism of carbon source on phosphate uptake etc.The research of this program posts the existence of a significant, yet previously unrecognized, microbial response to nutrient limitation which may be of importance for phosphate-cycling in the biosphere. The research results enrich the current theory of biological phosphorus removal, may exploit a potentially simple strategy for Pi removal. Therefore, this study has important theory meaning and wide apply foreground.