Treatment Of Bathing Wastewater With Non-woven Membrane Bioreactor

In order to overcome the problem of high cost of membrane modules, low costnon-woven material was used as the membrane of MBR to treat bathing wastewater,which had the characteristics of high efficiency and easy maintenance.In this work, by the comparison of the interception capability of a variety ofpolyster non-wovens with the short-term test, a kind of non-woven which had thebest interception capability and the strongest capability of anti-membrane foulingwas selected as the membrane material for MBR. The physical and chemicalproperties of the non-woven, such as surface structure, membrane pore sizedistribution, porosity, etc, were analized. Besides, the filtration chatacteristics of thenon-woven including the clean water flux and critical flux were also investigated.Based on the pre-test results, the non-woven membrane bioreactor （NWMBR）was established for bathing wastewater treatment. The treatment performance ofNWMBR was investigated. The results showed that the stable operating time ofNWMBR was more than three months under the operating conditions: volume loadof0.62kgCOD/m³·d, HTR of9.7h （aerobic tank:7.1h; anoxic tank:2.6h）,membrane flux of11.5L/m²·h and MLSS of5g/L. NWMBR had a goodperformance for bathing wastewater treatment. COD, BOD₅, NH₃-N, LAS andturbidity in the effluent were less than20mg/L,5mg/L,0.5mg/L,0.5mg/L and0.5NTU, respectively, which reached “Municipal Wastewater Reclamation andReuse: Standard for Miscellaneous Water Consumption”.The membrane fouling process of the NWMBR was studied, it was concludedthat the operating stability and the membrane fouling mechanism were different invarious operating stage. During the beginning stage of operating, the mean pore sizeof non-woven was nearly coincided to the average particle diameter of activatedsludge, which caused the pore blocking of non-woven membrane pores by particles,colloids or microorganisms. The measures controlling membrane flux below acertain range and providing a certain frequcey of clean water backwash werethought to be effective to alleviate the rapid occurrence of membrane fouling. Aftera period of operating, the mean pore size of non-woven was decreased due to thedeposition of suspend solids in the membrane pores, which leaded to the formationof the stable cake layer on the membrane surface. The cake layer could protect the suspend solids from enter into the membrane pores, thus prolonged the stableoperating time of NWMBR.In the long-term operating stage, reasonable controlling of the MLSSconcentration and the membrane flux were essential to alleviate the occurrence ofmembrane fouling. When MLSS was5g/L, the length of stable operating time wasmore than130days. With the MLSS increasing to9g/L, the length of stableoperating time declined significantly. It was because when NWMBR operated with ahigh MLSS concentration, the activated sludge could generate a large amount ofdeposition on the non-woven surface within a short period of time, causing the rapidincrease of trans-membrane pressure.Different operating condition of imposed flux transformed the cake layermorphology and structure, which caused dissimilar fouling characteristics ofNWMBR: when the membrane flux exceeded the critical flux, a thin and dense cakelayer formed rapidly and leaded to serious membrane fouling. When the membraneflux was lower than the critical flux, a loose and thick filamentous bacteria layerformed on the surface of non-woven, which could be acted as a secondarymembrane to prevent the particles, colloids and microbial metabolites fromadsorbing onto the membrane surface, which prolonged the stable operating time ofNWMBR.Furthermore, between each operating stage, the cake layer could be washed byclean water, which caused the membrane flux recovered to the level beforemembrane fouling. When serious membrane fouling occurred, sodium hypochloritebackwash was the best cleaning method for non-woven membrane, which leaded tothe recovery rate of clean water flux of non-woven membrane reached to98%.