Study On The Treatment Of Alkali Decrement Printing And Dyeing Wastewater By Self-Forming Dynamic Membrane Bioreactor

Self-forming dynamic membrane bioreactor(SFDMBR) makes up for the shortcomings of the traditional MBR,because its membrane has the advantages of low cost, low energy consumption, and high flux recovery from membrane fouling.SFDMBR is an effective solution to popularize the membrane technology.But compared with traditional membrane technology,the SFDMBR is still unreliable for the lacking of the thorough systematical investigation on system operation stability,membrane fouling mechanism.In this study,the membrane module of SFDMBR made by non-woven with pore size5μm and50μm were applied to the treatment of alkali-decrement printing and dyeing wastewater which had been treated with anaerobic baffled reactor (ABR).The operational conditions,treatment efficiencies, the activity of the biomass in the reactor, membrane fouling characteristics and its control strategies were investigated. The main results are as follows:(1) The membrane pore size has significant effect on the initial flux of the self-forming dynamic membrane,but when the dynamic membrane has been formed steadily,the membrane flux of nonwovens with different pore sizes tend to be consistent,the variation of pore size has silight effect on stable membrane flux in SFDMBR. The critical condition was that the water head drop(WHD) was18cm determined by the intermittent pressure step method.(2) The forming speed of self-forming dynamic membrane is related with aeration intensity, sludge concentration and WHD.In this experimental system, in order to keep the reactor running steadily,aeration intensity should be controlled around3.13m3/m2-h,WHD should be contolled between5cm and18cm, sludge concentration should be kept between4500mg/L and6500mg/L.(3) In the conditions of experiment, the removal efficiencies of COD, UV254, chromacity and turbidity in alkali-decrement printing and dyeing wastewater were74%～-85%,74%～79%,79%～86%, and96.8%～98.6%respectively by SFDMBR. The quality of effluent water was better than the first grade effluent standards (GB4287-92). The effluent quality of self-forming dynamic membrane formed on the nonwoven with the pore size of5μm was slightly little better,(4) The DHA in activated sludge of mixed liquid in SFDMBR was at elevated state at beginning, it tended to be stable at later period; The DHA in mixed liquid sludge was higher than the DHA in non-woven self-forming dynamic membrane, the DHA in self-forming dynamic membrane of the nonwoven with the pore size of5μm and50μm were slightly different, the latter was higher than the former. (5) The resistance of membrane fouling mainly comes from the cake layer resistance, followed by the irreversible resistance in SFDMBR, and the inherent resistance of membrane can be ignored.(6) During the process of the operation of reactor, the bond EPS (EPSB) were significantly higher than that of soluble EPS (EPSs) in EPS of sludge mixed liquor and self-forming dynamic membrane in SFDMBR, and the protein/polysaccharide (P/C) was generally greater than1. The impact of EPSB-protein on resistance of self-forming dynamic membrane is predominate, followed by the impact of EPSS-protein.The nonwoven membrane with the pore size of5μm had more contents of EPS than that of50μm.(7) During the process of the operation of reactor, the contents of EPSs in mixed liquid increased first and then decreased, and then gradually became stable; the contents of EPSB had a certain rising trend overall, in which EPSB-protein content increased, EPSB-polysaccharide slightly reduced.(8) The inorganic composition of membrane fouling is miscellaneous and complex,it is found to be Al, Si, Ca, Fe and other elements,they may be in the sulfate, carbonate, chloride, silicate, hydroxide or oxide form deposited on the membrane surface.(9) After hydraulic flushing and manual scrubbing, and soaking with O.lmol/L HC1and0.1%NaOH for1h, the membrane components can obtaine good effect of flux recovery, dynamic membrane flux of nonwoven with the pore size of5μm can be recovered to96.5%of the flux of unpolluted nonwoven, dynamic membrane flux of nonwoven with the pore size of50μm can be recovered to78.1%of the flux of unpolluted nonwoven.The main reason of the bad flux recovery effect was that sludge was easier to enter the membrane material with the big pore size.The results of this research can provide experimental basis for the development of SFDMBR which is a low running cost, easy operation and management treatment process for alkali decrement printing and dyeing wastewater. The operating parameters and control measures of membrane fouling are provided with great guiding significance.