Periodic chemical cleaning with sodium hypochlorite(NaClO)is essential to restore the membrane permeability in a membrane bioreactor(MBR).However,the chlorination of membrane foulants results in the formation of disin...Periodic chemical cleaning with sodium hypochlorite(NaClO)is essential to restore the membrane permeability in a membrane bioreactor(MBR).However,the chlorination of membrane foulants results in the formation of disinfection by-products(DBPs),which will cause the deterioration of the MBR effluent and increase the antibiotic resistance in bacteria in the MBR tank.In this study,the formation of 14 DBPs during chemical cleaning offouled MBR membrane modules was investigated.Together with the effects of biofilm extracellular polymeric substances(EPS),influences of reaction time,NaClO dosage,initial pH,and cleaning temperature on the DBP formation were investigated.Haloacetic acids(HAAs)and trichloromethane(TCM),composed over 90%of the DBPs,were increasingly accumulated as the NaClO cleaning time extended.By increasing the chlorine dosage,temperature,and pH,the yield of TCM and dichloroacetic acid(DCAA)was increased by up to a factor of 1–14,whereas the yields of haloacetonitriles(HANs)and haloketones(HKs)were decreased.Either decreasing in the chlorine dosage and cleaning temperature or adjusting the pH of cleaning reagents toward acidic or alkaline could effectively reduce the toxic risks caused by DBPs.After the EPS extraction pretreatment,the formation of DBPs was accelerated in the first 12 h due to the damage of biofilm structure.Confocal laser scanning microscopy(CLSM)images showed that EPS,particularly polysaccharides,were highly resistant to chlorine and might be able to protect the cells exposed to chlorination.展开更多
Precipitation of calcium carbonate (CaCOs) scale on heat transfer surfaces is a serious and expensive problem widely occurring in numerous industrial processes. In this study, we compared the scale inhibition effect...Precipitation of calcium carbonate (CaCOs) scale on heat transfer surfaces is a serious and expensive problem widely occurring in numerous industrial processes. In this study, we compared the scale inhibition effect of six kinds of commercial scale inhibitors and screened out the best one (scale inhibitor SQ-1211) to investigate its scale inhibition performance in highly saline conditions at high temperature through static scale inhibition tests. The influences of scale inhibitor dosage, temperature, heating time and pH on the inhibition efficiency of the optimal scale inhibitor were investigated. The morphologies and crystal structures of the precipitates were characterized by Scanning Electron Microscopy and X-ray Diffraction analysis. Results showed that the scale inhibition efficiency of the optimal scale inhibitor decreased with the increase of the reaction temperature. When the concentration of Ca^2+ was 1600 mg/L, the scale inhibition rate could reach 90.7% at 80℃ at pH 8. The optimal scale inhibitor could effectively retard scaling at high temperature. In the presence of the optimal scale inhibitor, the main crystal structure of CaCOs changed from calcite to aragonite.展开更多
基金the National Natural Science Foundation of China(Grant No.51808316)the Natural Science Foundation of Shandong Province(Grant No.ZR2019BEE015).
文摘Periodic chemical cleaning with sodium hypochlorite(NaClO)is essential to restore the membrane permeability in a membrane bioreactor(MBR).However,the chlorination of membrane foulants results in the formation of disinfection by-products(DBPs),which will cause the deterioration of the MBR effluent and increase the antibiotic resistance in bacteria in the MBR tank.In this study,the formation of 14 DBPs during chemical cleaning offouled MBR membrane modules was investigated.Together with the effects of biofilm extracellular polymeric substances(EPS),influences of reaction time,NaClO dosage,initial pH,and cleaning temperature on the DBP formation were investigated.Haloacetic acids(HAAs)and trichloromethane(TCM),composed over 90%of the DBPs,were increasingly accumulated as the NaClO cleaning time extended.By increasing the chlorine dosage,temperature,and pH,the yield of TCM and dichloroacetic acid(DCAA)was increased by up to a factor of 1–14,whereas the yields of haloacetonitriles(HANs)and haloketones(HKs)were decreased.Either decreasing in the chlorine dosage and cleaning temperature or adjusting the pH of cleaning reagents toward acidic or alkaline could effectively reduce the toxic risks caused by DBPs.After the EPS extraction pretreatment,the formation of DBPs was accelerated in the first 12 h due to the damage of biofilm structure.Confocal laser scanning microscopy(CLSM)images showed that EPS,particularly polysaccharides,were highly resistant to chlorine and might be able to protect the cells exposed to chlorination.
基金supported by the Major Bidding Projects in Shandong Province (No. SDZS-2012-SHBT01)
文摘Precipitation of calcium carbonate (CaCOs) scale on heat transfer surfaces is a serious and expensive problem widely occurring in numerous industrial processes. In this study, we compared the scale inhibition effect of six kinds of commercial scale inhibitors and screened out the best one (scale inhibitor SQ-1211) to investigate its scale inhibition performance in highly saline conditions at high temperature through static scale inhibition tests. The influences of scale inhibitor dosage, temperature, heating time and pH on the inhibition efficiency of the optimal scale inhibitor were investigated. The morphologies and crystal structures of the precipitates were characterized by Scanning Electron Microscopy and X-ray Diffraction analysis. Results showed that the scale inhibition efficiency of the optimal scale inhibitor decreased with the increase of the reaction temperature. When the concentration of Ca^2+ was 1600 mg/L, the scale inhibition rate could reach 90.7% at 80℃ at pH 8. The optimal scale inhibitor could effectively retard scaling at high temperature. In the presence of the optimal scale inhibitor, the main crystal structure of CaCOs changed from calcite to aragonite.