| In recent years, membrane bioreactor (MBR) for wastewater treatment and reuse isgreatly esteemed and concerned by scholars and professionals. However, membranefouling is still the technical problem which has not yet been well-solved. The object of thispaper was the membrane fouling control of submerged MBR (SMBR) pilot-scale system inwastewater treatment. Based on results of the moderate sludge retention time (SRT) andthe optimal aeration mode and intensity, adsorption-MBR hybrid system by adding MARto MBR was investigated to control membrane fouling in domestic wastewater treatment,and precoagulation-MBR hybrid system was investigated to achieve membrane foulingcontrol and reuse organics in dairy wastewater treatment. Cleaning methods of the fouledmembrane were also investigated in the treatment of local domestic wastewater. The mainresults obtained in this paper are as follows:Firstly, the moderate SRT of SMBR treating domestic wastewater was determined bystudying the impact of SRT on mixed liquor suspended solids (MLSS), food-to-microorganism ratio (F/M), polysaccharide (PS) concentration of extracellular polymericsubstances (EPS), chemical oxygen demand (COD) and ammonia nitrogen (NH4+-N)removal. Extending SRT could increase the MLSS concentration and decrease the F/M andthus could enhance the removal of foulants and reduce the production of excess sludge.However, the low F/M increased the number of microorganisms suffering endogenousrespiration when SRT was higher than40d, and therefore the microbial activity wasdecreased although the MBR with high MLSS and the biological treatment performancecould not be stably maintained. PS concentration of EPS affects the characteristics ofactivated sludge and the development of membrane fouling. This parameter as the selectioncriteria, suggested the moderate SRT should be controlled in less than40d. Results of thebiological removal of COD and NH4+-N showed that pollutant removal reached the bestlevel and almost unaffected by SRT when SRT was in the range of20-40d. Consideringthe three aspects of microbial activity, membrane fouling and effluent quality, theappropriate SRT was20d≤SRT＜40d under the conditions of this experiment.The aeration mode and the aeration intensity were further determined by investigatingtransmembrane pressure (TMP), critical flux (CF), microorganisms’ type and size, resistance of different mixed liquor fractions, COD and NH4+-N removal. Continuousaeration was the most effective strategy for the mitigation of membrane fouling althoughintermittent aeration in the relaxation phase played an important role in the cake layerremoval. Therefore, optimizing aeration intensity in the mode of continuous aeration hadmore practical significance to balance the relationship between energy consumption andmembrane fouling rate. Short-term results by measuring CF showed that increasingaeration rate could enhance the cross-flow velocity, reduce the deposition of suspendedparticles on membrane surface, and so mitigate the membrane fouling. Nevertheless, theresults of long-term running experiment found that increasing the aeration intensitychanged the characteristics of activated sludge, increased the possibility of membranefouling, and decreased the selectivity of the system for influent quality and the nitrifyingbacteria activity. Therefore, the aeration intensity should be determined according to theexperimental needs of hybrid system in subsequent studyMembrane fouling control of adsorption-MBR hybrid system with macroporousadsorption resin (MAR) treating domestic wastewater was researched through comparativeexperiments. Characterization of the critical flux showed the effect of membrane foulingcontrol in this hybrid system. Evolution of the sludge layer on membrane surface andchange of the mixture properties revealed the pathway of membrane fouling control in thishybrid system. Finally, regeneration experiment of the used adsorption resin was carriedout. The results showed that the critical flux could be improved by adding powderedactivated carbon (PAC) and MAR to MBR, and resin showed excellent result particularly.The scouring of MAR on membrane surface and the improved filterability of sludgemixture were the ways to realize fouling control. Adsorption-MBR hybrid system withMAR could reduce the foulant loading in bioreactor, decrease sludge production and wouldbe better than the adsorption-MBR hybrid system with PAC in operating costs due to therenewable performance of resin.Physical cleaning and chemical cleaning are determined and used for the cleaning ofcontaminated membrane by model fitting of experimental data and fourier transforminfrared spectroscopy (FTIR) analysis of foulants. Effect and rationality of the cleaningprocedure was tested by scanning electron microscope (SEM) image analysis and specificflux (SF). The results found that the decline of membrane flux was mainly affected by the formation of cake layer. Proteins, polysaccharides and lipids were the major foulants oforganic fouling. Physical cleaning can effectively remove the fouling caused by thedeposition of sludge floc, and chemical cleaning was the important means to removestrongly attached organic fouling and inorganic fouling caused by pore blocking. Waterflux of membrane showed that the flux could be restored more than90%of the newmembrane flux by the cleaning procedure used in this paper, and irreversible fouling couldnot be removed by this cleaning process.In order to achieve membrane fouling control and reuse the organics in wastewater,precoagulation-MBR hybrid system coupling precoagulation process with MBR was usedfor dairy industrial wastewater treatment of Inner Mongolia. By jar test, turbidity removalefficiency of the actual dairy wastewater using four typical coagulants of alum, aluminumsulfate, ferric chloride and polyaluminium chloride were investigated. Then, coagulant typeand its dosage, influent pH and settling time were determined. The overall applicationperformance of the precoagulation-MBR hybrid system was compared with the presentprocess of dairy wastewater treatment plant in effluent quality (turbidity, COD and residualaluminum) and TMP change. The superiority of the precoagulation-MBR hybrid system inmembrane fouling control was indicated by comparing the CF of the hybrid system withprecoagulation-microfiltration (Precoagulation-MF) hybrid system. The results showedthat polyaluminium chloride could be used as the optimal coagulant to reduce the organicloading in the hybrid system. Turbidity removal efficiency could reach98.95%when theinfluent pH was7.5and the dosage of polyaluminium chloride was900mg/L. Effectivesettling time was30min. Precoagulation process of the hybrid system played a veryimportant role in stabilizing the effluent quality of MBR and improving the membraneperformance. MBR could removal the residual turbidity and aluminum in precoagulationeffluent better than the existing treatment system, and it had the capability to resist shockloading and maintain the high COD removal. Compared with precoagulation-MF hybridsystem, precoagulation-MBR could control membrane fouling successfully. |
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