Research And Engineering Application Of High-Efficiency Phosphorus Removal Agent And Phosphorus Resource Recovery Technology In Sewage Treatment

This thesis was based on the Key Environmental Pollution Control Project of Baotou City,Inner Mongolia Autonomous Region,named‘Upgrade,reorganization and expansion,wastewater reuse and pipe network project of a wastewater treatment plant located in Baotou’（Baotou Development and Reform Commission,[2013]No.234）.The total phosphorus（TP）concentration of the effluent from a wastewater treatment located in Baotou City is hard to meet the discharge standard of grade 1-A of“National Standards of People’s Republic of China-Discharge standard of pollutants for municipal wastewater treatment plant”.In order to solve this problem,the component of the residual phosphorus in the effluent was detected to analyze the reason why the effluent couldn’t reach the discharge standard of TP.An efficient phosphorus removal agent was developed for simultaneous removal of inorganic phosphorus（IP）and organic phosphorus（OP）,the demonstration application research was also carried out in a local municipal wastewater treatment plant.Meanwhile,an automatic control system based on discrete fuzzy PID controller was developed to achieve the automatic control of the accurate dosing of phosphorus removal agent.Furthermore,the phosphorus recovery technical route of sewage sludge with high phosphorus content after the addition of phosphorus removal agent was preliminarily discussed and feasible alternative was proposed.The main results are as follows:（1）Aiming at the problem that the TP in the effluent from a wastewater treatment plant located in Baotou couldn’t meet the discharge standard,the component of the TP has been analyzed.The results showed that the high OP concentration（0.36-0.51 mg/L,accounting for 54.4%-80.0%of the TP concentration）in the effluent from the aerobic zone of the biological treatment process was the main reason for the exceeded TP.For the purpose of simultaneous removal of IP and OP,an efficient phosphorus removal agent was developed from magnesium-base gel compound after quaternarization based on the synergy of coagulation and adsorption.The effects of basicity,quaternary ammonium salt content,and intrinsic viscosity（η）on the Zeta potential of phosphorus removal agent were investigated and the optimum parameters were obtained.The results of characterization and adsorption characteristics indicated that the removal of OP was achieved by the adsorption function of the small particles from the hydrolysates of the magnesium-base gel compound after quaternarization,and the removal of IP was achieved by the coagulation sedimentation of PFAS.（2）The optimum dosing point and dosage were determined based on the results of process operation through the practical application test of the efficient phosphorus removal agent.The results of the field test showed that the best removal efficiency of TP could be obtained by adding the phosphorus removal agent in the distributing well of the secondary sedimentation tank.Decreasing TP concentration was observed with the dosage of phosphorus removal agent increased from 3.0 to 7.5 mg/L.TP concentration below 0.5 mg/L of the effluent could be achieved with the dosage of 6.0mg/L.The average removal rate of TP,OP and IP in the influent of distributing well of the secondary sedimentation tank was 71.72%,77.35%and 64.01%,respectively.The analysis of microbial community in the biological reaction tank showed that the microbial flora structure of the anaerobic,anoxic and aerobic stage remained stable before and after the addition of phosphorus removal agent.The long-term application results indicated that the removal rate of TP could reach 87%with the TP concentration of the effluent below 0.5 mg/L.Meanwhile,the other water quality indexes（COD、BOD₅、SS、TN、NH₃-N）could also meet the grade 1-A discharge standards.The phosphorus removal agent has been applied to four wastewater treatment plants located in Baotou with the treatment capacity of 235 000 t/d and annual sales of 7.743 million yuan.（3）Based on the discrete fuzzy PID controller,an automatic control system for the addition of phosphorus removal agent was developed and applied to the practical operation in the wastewater treatment plant.The auto-control of the addition of phosphorus removal agent has been achieved by the application of the data collection of TP concentration,data feedback,fuzzy operation,PID operation and dosing pump control.The comparison of the TP concentration and dosage before and after the application of the automatic control system indicated that the dosage could be reduced by about 31%with the reagent cost reduction of 1.27 million yuan.The problems of high dosage of phosphorus removal agent and the instability of TP concentration caused by manual dosing could be solved,and the precise control of the phosphorus removal agent addition could be achieved.（4）The study on technical route of phosphorus recovery was carried out to solve the phosphorus recovery from the sewage sludge（TP content was 34.5%higher than the sewage sludge before the addition of phosphorus removal agent）with high phosphorus content produced after the addition of phosphorus removal agent.The results showed that TP of the liquid supernatant was over 180 mg/L after thermal hydrolysis treatment（180 ^oC,60 min）and mesophilic anaerobic digestion,with phosphate content over 94%.After the treatment of sludge supernatant by magnesium ammonium phosphate method,the phosphate removal rate could reach 90.1%with struvite recovery rate of 97.1%.The technical route‘thermal hydrolysis treatment-anaerobic digestion-magnesium ammonium phosphate’was proved to be feasible for phosphorus recovery.