Study On The Formation Of Microbial EPS And Membrane Fouling Under The Stress Of Toxicants In MBRs

Membrane bioreactors(MBRs) have many advantages compared with traditionalwastewater treatment methods, but membrane fouling remains a major obstacle to theirwide application. Although the extracellular polymeric substances(EPS) are the maincomponents of activated sludge flocs and play significant roles in wastewater treatmentproeess, EPS are considered a major factor in membrane fouling. With the continuousrising proportion of industrial wastewater in municipal sewage, it becomes urgent tomake comprehensive study on the formation and action mechanism of EPS under thestress of toxicant in industrial wastewater. Thus can provide an important theoreticalbasis for better application of MBRS in industrial wastewater treatment. This thesismainly studies the production, composition and morphology of EPS and the membranefouling rule under the stress of simulative industrial wastewater, at the same time,makes further study on the EPS ecology effect and its mechanism. The main researchcontents and results are as follows:The production, composition and molecular weight distribution of EPS and themembrane fouling rule were invistigated in3parallel running MBRs coupled withfunctional resin: MBR1(without adding resin, as a control system), MBR2(added2g/L resin), MBR3(added4g/L resin). The results showed that the EPS production ofMBR2was less. When the organic load rate(OLR) increased from1to3kgCODm-3day-1, the average yields of EPS in MBR1, MBR2, MBR3increased from81.2,72.9,75.2mg/g to123.21,95.4,169.1mg/g respectively. P/C values changedfrom0.52,0.70,0.45to0.47,0.45,0.23, the proportion of polysaccharide increased.As the resin dosage increased, reducing the macromolecules in EPS production, theMW>100kDa proportion of EPS in three MBRs were16.7%,6.8%and2.2%. Themembrane fouling process slowed down with the resin dosage increased. In30days, theaverage values of total fouling of MBR1, MBR2, MBR3were6.065,2.922,1.937g/m2,the irreversible fouling average values were103,66and52mg/m2. The microbial community characteristics: SOUR, SCOD-UR, SVI, sludge particlesize distributions of MBR1, MBR2, MBR3were detected simultaneously. When theOLR increased from1to3kgCODm^-3day^-1, SOUR mean values changed from29.5,34.9,27.4to9.1,22.9,12.5mgO₂gVSS^-1h^-1.The SCOD-UR mean values decreasedfrom84.3,101.2,93.7to44.8,79.2,48.8mgCODgVSS^-1h^-1.There was a good linearcorrelation between SOUR and SCOD-UR. The SVI average changed from40.9,47.4,42.6to37.7,46.0,30.8mL/g. Accordingly, adding proper amount of functional resin inMBRs can remise phenol stress on microbials, ensure the microbials communityactivities, and make the activated sludge be stable and sustainable. The sludge averageparticle size rule was M_z3<M_z1<M_z2, proved that the2g/L amount of resin couldpromote the granulation of activated sludge.The production, composition and MWD of EPS, as well as the membrane foulingwere explored in5parallel running MBRs (numberd from A to E) under phenol-copperion combined stress. Phenol concentration was fixed at115mg/L, with the inlet copperion concentration increased continuously, the EPS yeilds per unit weight of the activatedsludge of reactors A-E were7.00,10.18,9.61,4.28and6.06mg/gMLSS respectively.This indicated that low concentration of copper ions promoted the generation of EPS,but too many copper ions might lead to substantial direct death of microbial. Copperions especially at low concentrations promoted macromolecular EPS' formation.Microorganisms were simulated to produced more polysaccharide than protein, the P/Cratios of five reactors were0.2031,0.1443,0.1449,0.1889and0.2180. On the aspect ofmembrane fouling, among five reactors, reactor B had accumulated the least totalfouling on both PES and MCE membranes, irreversible fouling was smaller as well. Thepollution degree of PES membrane was lower than MCE film, and the content ofprotein of irreversible fouling on PES was higher than polysaccharide.Simultaneously, the EPS extracted from the above reactors A-E were furtherstudied on their quenching effect on O₂.-and·OH, to compare the EPS' antioxidantproperties. The results were as follows: On the first day after copper added, the averagevalue of quenching ability of1mg/L EPS had on O₂.-were2.7009,1.2527,5.2220,3.1663and6.4368μg/LSOD, in three days were2.7666,2.3790,4.0443,3.8309and5.5196μg/LSOD individually. On the50th and70th day, the quenching ability EPShad on O2.-didn't change in the control systerm but decreased notably as time goes by in B to E reactors. The mean values of the scavenging effect1mg/L EPS had on OHon first day were2.3355,0.2516,1.1864,2.4064and1.9146mg/LVc separately for fivereactors, in three days were1.2851,0.2071,1.5963,1.4767and2.4206mg/LVc. On50thand70th day, EPS sample from the control system had no scavenging effect on OH,EPS samples from other four systerms had slight scavenging effect on OH, normallyonly2%-10%of that in the first3days. These facts indicated that microbial EPS ofdifferent systems have different antioxidant properties, and play an important role inpreventing oxidative damage.