Analysis Of The Influencr Of Fe³⁺ On MBR Performance

Membrane bioreactor(MBR) has been considered as one of the most promising processes for wastewater treatment and reclamation, providing many advantages of high quality product water, modular design with less space requirement compared with conventional activated sludge systems(CAS). However, membrane biofouling due to microbial attachment onto membrane surface would cause a reduction in the flux and limit its widespread application in water treatment. therefore, the aim of this work is to seek a strategy of membrane fouling mitigation in a MBR with iron addition.The submerged membrane bioreactor was adopated to investigate the mechanism of retarding membrane fouling under the dosage of Fe Cl3 at 10 mg/L. The impact of Fe Cl3 addition on the performance and membrane fouling in MBR was investigated. The main results were obtained as follows:(1) The effects of ferric chloride addition on performance of MBR were investigated, the results showed that Fe3+ additive is an effective approach for the performance improvement in the both pollutants removal and membrane fouling reduction. Compared with the control reactor, the removal of COD, NH4+-N and TP was obviously enhanced by addition of 10 mg/L Fe Cl3, which was 94.5±1.3%、97.3±1.2% and 89.1±1.2%, respectively. Furthermore, the addition of Fe3+ resulted in a significant improvemrnt in the modified fouling index(MFI) and a remarkable decrease in the trans-membrane pressure(TMP), which would be beneficial to the mitigation of membrane fouling.(2) The characteristics of mixed liquor in MBR changed a lot under the addition of ferric chloride. The lower sludge volume index(SVI) was observed at the presence of iron, indicating that iron can improve the sludge settling performance by the help of mutilent cations. On the other hand, the zeta potential and dynamic viscosity slightly decrease. With the operation time, Fe3+ additive can reduce the content of microbial metabolites, both soluble microbial products(SMP) and extracelluar polymeric substances(EPS) contents were decreased obviously. In addition, a significant reduction in the SMP polysaccharide, loosely bound EPS(LB) and(tightly bound extracellular polymeric substances TB) amount were observed under the addition of iron condition.(3) The distributions of iron were investigated in MBR under the condition of ferric chloride at concentrations of 10 mg/L in the effluent. The experimental results showed that iron content in the cake layer and gel layer accounted for 12.5% and 4.7% of the total iron content in MBR, respectively, the majority of ions located in the in the mixed liquor(82.8%), the iron contents located in the sludge following this order: pellet > TB > LB >SMP. After the day 80, the majority of ions located in the pellet(81.2% on average), indicating that iron has a tendency form the supernatant to the core of sludge with the operation time in MBR.