Impact of phosphorus removal agents on precise evaluation of biological phosphorus removal efficiency and improvement strategies

In the operation of wastewater treatment plants （WWTPs）， a rather critical issue has emerged where the biological phosphorus removal efficiency is often unable to be precisely characterized because of the influence of the residual chemical phosphorus removal agents in the system， which in turn gives rise to the problem that excessive amounts of phosphorus removal agents are dosed， not only causing waste of resources but also potentially disrupting the normal operation and performance of the WWTPs. In this paper， a combined approach integrating bench-scale tests in a laboratory setting and on-site tests mirroring the actual operation conditions of WWTPs was adopted to clearly expound the impact of chemical phosphorus removal agents on the evaluation of biological phosphorus removal efficiency. When constructing the evaluation system for biological phosphorus removal efficiency， several key characterization indicators such as polyphosphate which is of great importance in the processes of phosphorus storage and release within the biological systems of WWTPs， polyphosphate-accumulating organisms （PAOs） which are the core microorganisms in phosphorus accumulation， and poly-β-hydroxybutyrate （PHB）， an essential metabolite closely related to the energy metabolism and phosphorus removal， were chosen， and integrated with the analytic hierarchy process（AHP） to establish a brand-new and comprehensive evaluation system for biological phosphorus removal efficiency. Subsequently， the evaluation of biological phosphorus removal efficiency was carried out for three WWTPs in Beijing with different treatment processes. Based on the evaluation results， targeted improvement strategies were put forward. The results showed that the residues of chemical phosphorus removal agents remaining in the system can seriously affect the accuracy of the evaluation results of biological phosphorus removal efficiency. In the case of WWTP A， the error exceeded 40%. This led to the inability to accurately dose phosphorus removal agents， thereby greatly interfering with the operation and regulation of the WWTP. Fortunately， the newly developed evaluation method can effectively eliminate the influence and obtain the accurate proportion of biological phosphorus removal in the wastewater treatment process， with an evaluation accuracy higher than 95%. When conducting the evaluation of biological phosphorus removal in WWTPs， it is recommended to mainly focus on detecting the changes in sludge polyphosphate， and take the detection results of the abundance of PAOs and PHB as supplementary information. By combining these three evaluation indicators and dynamically adjusting the operating parameters of the biological tank in the WWTP， and the dosing amount of phosphorus removal agents， the strengthening of biological phosphorus removal and the accurate dosing of phosphorus removal agents can be achieved， thus improving the overall operation efficiency and environmental protection level of the WWTP.