| As a new water treatment technology, Membrane bioreactor (MBR) is widely usedin decentralized system for wastewater treatment and reuse in recent years. Membranemodule form often used in MBR process is mainly for the hollow fiber membrane(including most capillary mode) and flat-sheet membrane. Stand on the current researchand the practical application point of view, the domestic research on hollow fibermembrane MBR is more extensive than flat-sheet membrane. But the performance offlat membrane in sewage treatment efficiency and the extent of membrane fouling aresuperior to hollow fiber membrane. MBR system also has problems with high energyconsumption, effect of membrane pollution on water rate, complex membrane cleaningprogram and regular replacement of membrane components, of which the mostprominent problem is the membrane fouling. In this experiment, the campus sewagewas treated by A/O-MBR wastewater treatment system composed of flat-sheetmembrane bioreactor technology and anoxic/aerobic process. This experiment mainlyinvestigated the characteristics of the process for additional nylon mesh protective coversystem, stability of the film running and its impact on membrane fouling.Firstly, through the orthogonal test, when the reflux ratio is200%, the HRT is8hand the gas-water ratio of25:1, the A/O-MBR system will achieve the best treatmenteffect. The data showed the membrane module operation added nylon screen onremoving CODCr,NH3-N, TN, TP were slightly higher than the membrane componentof another group without protective measures. It is suggested that although the apertureof nylon filter is larger than microfiltration membrane, the self-forming dynamicmembrane can strengthen the interception performance, which improves the removalrate of pollutants in the system. Meanwhile, according to experimental results, theeffluent quality of A/O-MBR can meet the relevant requirements of water reusestandards, this system is feasible as the city greening water for reuse.Secondly, the smooth operation states of flat-sheet membrane and the fluxrestoration of cleaned flat-sheet membrane modules were observed to analyze the roleof nylon filters for reducing membrane pollution in this topic. It turned out that theflat-sheet membrane pollution has experienced three stages：conditioning fouling, slowfouling and TMP jump. When additional nylon membrane filter run, the conditioning fouling and slow fouling phase last longer, and the rate of membrane fouling is less thananother membrane module. Although the dynamic film forms on the surface of nylonfilter will cause a small growth of TMP, it can intercept part of the fine particulate anddissolved substances which reduced the membrane pore clogging and played a role inslowing flat membrane fouling. And internal pollution caused by pore blocking was themain factor of flat-sheet membrane fouling.Dynamic film make a small contribution tothe filtration resistance of flat-sheet membrane. The content of gel-layer EPS andmembrane fouling has a certain correlation. The dynamic film on the surface of nylonmesh could alleviate membrane fouling. Besides, a cleaning test was made on thecontaminated membrane modules. The total rate of membrane flux in the system wasrecovered greatly after water flushing+pickling+caustic washing method. The causticwashing achieved the best effect with the recovery rate. Thr cleaning method of nylonfilter is aeration, which can control the surface contamination of nylon filter. In addition,this experiment showed that a reasonable adjustment process of operating conditions areconducive to membrane fouling.Finally, the paper examines the economic utility of anoxic/aerobic flat membranebioreactor. Considering the fixed investment, the treatment effect and construction land,A/O-MBR process is economically feasible. This process as a wastewater treatment andreuse technology will have a more broad prospects for development based onsustainable development view. The acquisition cost of the flat membrane is a mainfactor of the A/O-MBR system investment costs. And the cost of sewage treatment andmembrane depreciation expense decreased obviously when adding a protective cover.This shows that the nylon screen protective cover can reduce operational cost of runningA/O-MBR, which has a certain practical significance and economic usefulness. |
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