Study On The Removal Of Phosphorus By The Enhanced Membrane Bioreactor And The Reclamation Of Phosphorus

Much phosphorus in the treated urban wastewater causes water eutrophication and phosphorus loss. Membrane Bioreactor (MBR) is gradually used in wastewater treatment for its good performance and excellent effluent except limited phosphorus removal. So, it is significant to study enhanced MBR phosphorus removal and phosphorus reclamation simultaneously.Firstly the effect of single Hybrid Membrane Bioreactor (HMBR) on treating domestic wastewater was studied. The removal efficiency of COD, NH4-N and SS were above 90% and TN was about 40% when the process was operated steadily.But the removal efficiency of P was bad. The chemical-coagulation pretreatment could make the TP in effluent under 1 mg/L. Pre-dosage was better than synergic dosage on phosphorus removal. The results of screening coagulant for phosphorus removal indicated that, the optimum addition method was selecting Al2(SO4)3 as coagulant and Ca(OH)2 at dosage no higher than 20mg/L, and the pH value of effluent was little fluctuating.Secondly the effect of External Recycle of Activated Sludge Processes- Hybrid Membrane Bioreactor(ERP-HMBR) on treating domestic wastewater was studied. In the steady state, the removal efficiency of COD and NH4-N were above 90% respectively, the removal efficiency of TN was about 70%. The removal efficiency of TP was determined by the amount of phosphorus release from external recycle sludge. The removal efficiency of P was steadly above 80% when the phosphorus releas from external recycle sludge is sufficient and less of 60% when the phosphorus releas was bad. The results of effecting factor analysise indicated that, suitable anaerobic phosphorus release time was 1.5².0h; when acetateas was used as phosphorus release carbon resource organic substrate, 1mmol phosphorus release need about 1.048mmol acetate.According to the characteristic that the ERP-HMBR process would produce less wastewater with higher phosphorus concentration, the impacting factors in the process of phosphorus reclamation were studied by batch tests used simulated high-phosphorus wastewater. During the reclamation process in which the main product was struvite, the best pH would gradually decrease with the increase of initial phosphorus concentration and eventually stabilized at about 8.5. If pH value was no more than 9, the disturbance of magnesium phosphorus to the struvite deposition could be neglected. If the initial phosphorus concentration was less than 35mg/L, it was not suggested toreclamation phosphorus in the form of struvite. When the ratio of [Mg²⁺]:[NH₃-N]:[P] increase gradually from 1:1:1 to 2:2:1, the phosphorus reclamation percentage would increase from 33.2% to 86.8%. Moreover the ratio of [NH₃-N]:[P] can affect the reclamation percentage more than the ratio of [Mg²⁺]:[P]. Phosphorus reclamation in the form of calcium phosphate was better than the form of struvite when there was much calcium ion in the wastewater. During the reclamation process in which the main product was calcium phosphate, the results of tests indicated that the best pH value for phosphorus reclamation would gradually diminish with the increase of initial concentration of phosphorus. Under the condition of best pH, the phosphorus reclamation percentage would gradually become stable with the increase of the ratio of calcium to phosphorus , it could come to 85% or more when the ratio of calcium to phosphorus was 2:1.The composition analysis of the phosphorus reclamation product indicated that, the mass percentage of main elements in struvite deposited from the reclamation process of simulated wastewater is approximately equal to the theoretic ratio, the mass percentage of phosphorus, magnesium and NH3-N was lower than the theoretic value because of the calcium disturbance. During the calcium phosphorus deposition process, the mass percentage of calcium and phosphorus in simulated wastewater approached to that in real wastewater, both of which were lower than the theoretic value, which indicated that the probable existence of crystal water in calcium phosphorus deposit may be the reason why the mass percentage of calcium and phosphorus was lower than the theoretic value.