Effects of polysaccharides and proteins in EPSs on DBP formation during iron release†

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.