Study On Optimization Operation Of Flat-sheet Membrane Bioreactor

In recent years the membrane bioreactor (MBR for short) has been widely used insewage treatment fields, mainly because of its high-quality effluent, but also because ofits space-saving compact design. However, with the increasingly stringent emissionstandards and the expansion of water treatment, employing a simple MBR systemmakes it difficult to meet the emission requirements. Therefore, optimization wasachieved in the study by using the anoxic/aerobic process (A/O for short) combinedwith the MBR system to enhance the effectiveness of nitrogen and pHospHorus removal.Moreover, to strengthen the system’s stability, a comparison system was added whichutilized suspended biological fillers. In addition, based on the currentmembrane-module problem, flat-sheet membrane modules were chosen to studycampus life sewage treatment and re-use, and were found to be superior in the aspectsof membrane fouling and membrane service life.Due to the addition of suspended biological fillers, the contact area between theraw water and microorganisms increased. In order to make a further estimate on theeffect of adding suspended biological fillers, a traditional membrane bioreactor system(A/O-CMBR for short) and an anoxic/aerobic hybrid membrane bioreactor system(A/O-HMBR for short) were operated in the same conditions, with CODCr,NH3-N, TN,TP, chroma and turbidity being detected. The data shows that after adding the8%ratioof suspended biological fillers in the aerobic tank, the quantity and variety ofmicroorganisms increased. The impact-resisting ability has also been improved. Also,the removal effects of NH3-N, TN, and TP have significantly increased. But before theexperiment began, suspended biological fillers were needed to be purchased. In order tocomprehensively evaluate the practicality of two systems as much as possible, theDelpHi method was used to evaluate weights, combined treatment results, economiccosts and operating conditions. The results showed that the A/O-HMBR system hadmore advantages in practical application.The experiment was launched to optimize the A/O-HMBR system. Through theorthogonal test, when reflux ratio was200%, HRT was8h, DO concentration was2.5mg/L~3.5mg/L, The major pollutants efficiency can be achieved. The results showedthat after optimization the removal efficiency of pollutant had improved a certain degree.In addition to the effluent concentration of TP, the rest of pollutant concentrations can all meet the standards of newly-built enterprise in level A. Whereas what the thesisfocused on was sewage reusing. The effluent concentration of TP was not demanded inthe water reuse standard of city pouring water, and other pollutant effluentconcentrations can all meet the standards of pouring water. Therefore, the effluent ofA/O-HMBR system for urban pouring is feasible.Finally, the thesis investigated content of EPS in the mixture volume when thesystems of A/O-CMBR and A/O-HMBR were in the contrast period. The result was thatEPS content in per-mixture volume of the former was obviously lower than the latter, sointervention of fillers could delay the membrane fouling. Membrane fouling underdifferent stages was investigated in the test through the method characterized by TMP,while the condition of membrane flux recovery after cleaning was also investigated. Theresults show that the flat-sheet membrane pollution mainly experienced three periods:smooth-running, slow development, and index jump. Through the establishing themathematical model, the main factors of flat-sheet membrane fouling were found:blocked-pore membrane adsorption of pollutants internal contamination. Three cleaningtests were operated. The methods of cleaning were water flushing+pickling+causticwashing. Three times after caustic cleaning, the membrane flux recovery achievedpercentages of95.5,97.2, and96.9, respectively. The effect of membrane-flux recoveryis best after caustic washing. In addition, from the view of slowing membrane fouling,impact mechanism was analyzed which included cross-flow filtration, batch unit,aeration-control intensity and sludge concentration of reaction. Therefore, to operateconditions in a reasonable way can reduce the rate of membrane fouling. In short, byusing the system of A/O-HMBR, the effluent water quality can meet major pollutionindicators of the standard in reclaimed water and level A.