Experiment Study On Wastewater Treatment Of Service Areas Of Highway By Combined Aeration Hybrid Membrane Bioreactor

In view of the present problems that wastewater treatment equipments didn’t operatenormally in majority of service areas of highway in our country, or effluent water qualitydidn’t achieve the national discharge standard as a result of the treatment effects were bad,and residents were very disgusted because of environmental pollution surrounding the serviceareas, and so on, the experiment study was presented to treat the wastewater of service areasof highway by combined aeration hybrid membrane bioreactor （MBR）. The techno-economicanalysis, of which wastewater treatment and water reuse project of service areas of highwayused by combined aeration hybrid MBR, was done finally. The results and conclusions of theexperiment study were as follows:（1） The test of start-up and commissioning of combined aeration hybrid MBR showedthat: it spend20days to reach a stable running since activated sludge inoculation, cultivationand acclimatization. Effluent water quality reached “The reuse of urban recycling water-Waterquality standard for urban miscellaneous water consumption”（GB/T18920-2002）, while totalphosphorus （TP） of effluent didn’t fulfil secondary standard in “Integrated wastewaterdischarge Standard”（GB8978-1996）. Microbiological examination found that there was a lotof zooglea and filamentous bacteria, many kinds of protozoa and a certain number of metazoain activated sludge, which showed that water purification was well and the system was stableas food chain was long.（2） In the orthogonal experiment of combined aeration hybrid MBR, four factors, whichis on/off ratio, mixed liquid suspended solid （MLSS）, hydraulic retention time （HRT） andgas-water ratio, were analysed to have influence to removal rates of chemical oxygen demand(COD_Cr), ammonia nitrogen （NH₃-N）, total phosphorus （TP） and turbidity. The optimaloperation parameters of the best wastewater treatment effect were that: on/off ratio was7min:3min, MLSS concentration was6⁹g/L, HRT was10h and gas-water ratio was20:1.（3） The pollutants removal effect in combined aeration hybrid MBR, added suspendedbiofilm carrier, was better than ones in integrated MBR, was also rasied from ones in runningby not added suspended biofilm carrier. Effluent water quality was superior to “The reuse ofurban recycling water-Water quality standard for urban miscellaneous water consumption”（GB/T18920-2002）.（4） Membrane resistance was measured to be14.047×10¹¹m^-1by the test of water fluxratio, and critical flux was determined to be25³0L/（m²Â·h） with the method of flux stepwiseincrement. The study of membrane fouling prevention found that: shortening suction time and lengthening pause time would retard membrane fouling. The optimal on/off ratio was7min:3min. The larger membrane flux was, the faster transmembrane pressure （TMP） rose,and the easilier membrane fouling formed. The optimal membrane flux was10.47L/（m²Â·h）.Aeration increase would slow down membrane fouling. However, over-intense aeration wouldhave the disadvantage factors and increase energy consumption. The optimal aerationintensity was176.5L/（m²Â·h）.（5） The study of membrane fouling control found that: water flushing improvedmembrane pollution obviously, but water flushing, which only removed membrane externalpollution of filter cake layer, couldn’t remove membrane internal pollution of adsorption andblocking of membrane hole. The only-aeration could reduced TMP effectively and restoredmembrane flux temporarily, which only removed part of sludge layer adhering membranesurface, couldn’t remove membrane internal pollution, too. The removal of membrane internalpollution could use the method of chemical cleaning.（6） Take a wastewater treatment and water reuse project of service area with the scale of200m³/d as an example for economic analysis, the energy consumption was0.55KW·h/m³,and the operation cost was0.349yuan/m³. Social benefit and environmental protectionanalysis showed that the reduction of pollutants discharge were that: COD_Crwas20.21tonsper year, NH₃-N was1.72tons per year, TP was0.25tons per year, and suspended solid （SS）was10.95tons per year.