Qiaojiao Mu,Hongtao Zhao,Yuan Zhuang,Yili Wang,Baoyou Shi
Corrosive iron pipes in drinking water distribution systems favor biofilm growth. A high protein-to-polysaccharide ratio could reduce the adhesion of biofilm on the pipe wall; however, the effects of the protein-to-polysaccharide ratio on disinfection by-product (DBP) formation are unclear. To investigate this issue, this study used bovine serum albumin (BSA) and sodium alginate (SA) to simulate proteins and polysaccharides in extracellular polymeric substances (EPSs), respectively, and systematically examined the effects of different protein-to-polysaccharide ratios on the generation of DBPs during chlorination disinfection. BSA promoted the formation of regulated DBPs, including trihalomethanes (THMs) and haloacetic acids (HAAs), as well as emerging DBPs such as haloacetonitriles (HANs), but SA did not obviously affect DBP formation. BSA also increased turbidity, enhanced particle dispersion, and led to the formation of a greater number of smaller iron particles. In contrast, SA promoted particle aggregation and sedimentation, resulting in reduced turbidity. Particle characterization further demonstrated that BSA exhibited stronger binding with iron particles than SA. Notably, from a toxicological perspective, BSA led to higher levels of cytotoxicity and genotoxicity due to the increased formation of DBPs. Thus, this study identified a new risk that a high protein-to-polysaccharide ratio increases the formation of DBPs promoted by the iron particle interface, besides the risk of microorganism release from pipe wall into bulk water.
The frequent occurrence of toxin-producing cyanobacteria blooms driven by anthropogenic eutrophication has become a major threat to aquaculture ecosystems worldwide. In this study, the behavior of M. aeruginosa cells during flocs storage period of 6 days was first investigated after pre-oxidation and coagulation of Fe 2+ /PS. Fe 2+ /PS achieved a superior removal efficiency of 90.7% for OD 680 and 90.4% for chl-a. The contents of extracellular MCs in the pre-oxidation and coagulation system were significantly ( P < 0.05) lower than those in the control. A significant ( P < 0.05) difference in intracellular protein between the control and the coagulated systems was observed. Three-dimensional fluorescence excitation emission matrix (EEM) was employed to investigate the variations in extracellular organic matter (EOM) during flocs storage. The results indicated the presence of four peaks, representing protein-like substances, intermediate dissolved microbial metabolites, fulvic and humic-like compounds in the Fe 2+ /PS process. And the intensities of four peaks were all decreased in the Fe 2+ /PS system compared to those in the control. A low level of accumulated residual Fe of 0.28 mg/L was observed without posing potential environmental risk. The results showed that the M. aeruginosa cells were under stressful conditions after 3-d storage due to the decomposition of extracellular polymeric substances (EPSs) and the insufficient supply of nutrients. However, SEM results indicated that no significant alteration in cell morphology was observed. Therefore, with high removal of M. aeruginosa , low MCs concentrations, and trivial cell damage, the Fe 2+ /PS preoxidation-coagulation was proved to be an environmental-friendly method for cyanobacteria removal without yielding serious secondary pollution. This work will contribute to better understanding and managing the cyanobacteria-laden aquaculture water after pre-oxidation and coagulation.
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