Study On Phosphorus Removal By Chemical Enhancement With Aluminum Sulphate And The Effects On Membrane Flux In MBR

Comparing to the Conventional Activated Sludge process(CAS),Waste water treatment by means of membrane bioreactor can greatly save water resources, equipment and operating cost. But the removal efficiency of TP is low by reason of long SRT of activated sludge in MBR. How to combine the treatment biochemical synergistic precipitation is the critical problem, when comes to have a high removal efficiency of organic compound, at the same time, strengthen the removal efficiency of TP.In this paper, artificial domestic wastewater was treated in submerged membrane bio-reactor. In the intermittent test, the best chemical coagulant and the quantity were confirmed. In the continuous test, phosphorus removal by biochemical synergistic precipitation was researched, at the same time, the effect of the mixed liquor, TMP and membrane flux was studied to show the change of membrane flux. The content of the experiment is depicted as follows:When the effect of COD,NH3-N and TP treatment efficiency was studied in Submerged membrane bio-reactor , the operation without sludge discharge for a long period ,it was found that the removal efficiency of COD and NH3-N is in the range of 93.13%～98.93% and 85%～99%respectively ,but the average TP removal efficiency is only 42.80%.Insoluble metal phosphate was hard to permeate though ultrafiltration membrane, so chemical method was adopted to improve the removal efficiency of TP in Submerged MBR. Aluminum salt is the suitable coagulant in this test, because the fouling of membrane would be grievous if the ferric salt were put into membrane bio-reactor .The pH of ferric salt which is suitable to get rid of TP is low, so it was disadvanted to microorganisms to survive in it.In the parallel test to choose the best aluminum salt, chemical of coagulant use aluminum salt. AlCl3, Al2(SO4)3 and PAC were put in three uniform reactor. It was found that PAC had a highest removal efficiency of TP, Al2(SO4)3 took second place, AlCl3 took the third place.According to the result of the stability of insoluble metal phosphates and removal efficiency of TP, the sequencing test was operated. It was found that the suitable ratio was Al3+ :TP is 1.5. The prime pH is 7.0～7.5.After Al2(SO4)3 was put into MBR, the effect of removal of TP was studied, it was found that when the influent TP is high(about 16mg/L), the average TP removal efficiency is 74.22%, at the same time, The average removal of COD and NH4+-N all above 94%. Al2(SO4)3 had little influence on the removal of COD and NH4+-N. When influent TP is low (about 3mg/L), the average TP removal efficiency is 75%. The discharge TP less than 1 mg/ L. Sludge was discharged once per four days in MBR.When the biofacies were observed by microscope , it was found that the different dominating species changed following this rule: Free swimming ciliate, epistylis rotans, arcella hemisphaerica, rotifers and aeolosoma hemprichicii became the dominating species in turn as the react time by, After aluminum salt was put in the reactor, the biofacies was simplex, arcella hemisphaerica which could suffer from the disadvantageous survival circumstance and aeolosoma hemprichicii which ate sludge chipping and organic grain became the dominateing species. But the number of microorganism was balance, so the quality of the effluent was not obviously affected.When the effect of the mixed liquor, TMP and membrane flux was studied after putting Al2(SO4)3 into the reactor, it was found that the mixed liquor and TMP were increased, membrane flux was decreased when the chemical of coagulant were put into the reactor .The reason is that the sludge of aluminum sedimentation is little agueous suspension flocs which easily became membrane pore plugge. There is an advisement that the quantity of Al2(SO4)3 should be further studied in order to have a high removal efficiency of TP and reduce the membrane flux simultaneity.The analysis of membrane resistance distribution shows that membrane pore plugge is the main foul of total resistance which is take the part of 49.17%.The proportion of inherent membrane resistance and cake resistance was respectively 28.58% and 22.25%. Cleaning the fouled membrane by water/NaClO/HCl could recover the membrane flux about 85.6% of new membrane flux. The proportion of water, NaClO and HCl was respectively 35.7%, 43.1% and 6.8% .The contribution of NaClO take the first place. Because it removed not only the gel layer but also the deposition which contained aluminum hydroxid.