Biofilm growth on PVC and HDPE pipes impacts chlorine stability in the recycled water

This study investigated the effects of pipe materials on biofilm growth in full-scale recycled water (RW) distribution system. A biofilm reactor containing high-density polyethylene (HDPE) and polyvinyl chloride (PVC) pipe coupons was fed directly with chlorinated water from the storage reservoir of a full-scale RW distribution system. The reactor was operated at a variable water flow rate of 0.08-0.30 L/min and free chlorine residuals of 0.05-0.7 mg/L. Total carbohydrate, biofilm thickness, biofilm mass, and extracellular polymeric substance (EPS) measurements showed that both HDPE and PVC pipe surface materials are susceptible to biofilm formation and there was no significant difference in biofilm formation between the two pipe materials used in this study. The difference between total chlorine and free chlorine was significant even in the presence of minimal ammonia-nitrogen (<0.066 mg/L) demonstrating chlorine is largely in the form of organic chloramines. Additionally, a significant role of biofilm in decaying chlorine demonstrates the need for biofilm management strategies to maintain water quality in the RW distribution systems.