DISINFECTION-DRIVEN OXIDATION AND THE EFFECT ON WATER QUALITY IN WATER DISTRIBUTION NETWORKS

Abstract

High-density Polyethylene (HDPE) pipes are widely used in drinking water distribution networks due to corrosion resistance, cost-effectiveness, and other practical advantages. However, they are susceptible to oxidative degradation caused by disinfection, particularly chlorine dioxide (ClO2), which can deplete antioxidants in the polyethylene. Furthermore, polymer-water interaction may release organic carbon that supports microbial growth, thereby affecting water quality. This study investigated oxidative degradation and the water quality impacts of HDPE under field and laboratory conditions representative of real network conditions. Field-exposed and laboratory-aged pipes exposed to 0.02 and 1 mg/L free chlorine resulting from chlorine dioxide were characterized using FTIR, XPS, SEM/EDS, OIT, and hardness test. Water quality parameters were evaluated using a bioassay to measure total organic carbon (TOC), assimilable organic carbon (AOC), and bacterial growth potential (BGP). Results showed that the virgin HDPE exhibited minor surface oxidation, as evidenced by an anhydride-type feature at the inner and outer walls, suggesting oxidation during manufacturing and/or storage prior to installation. At low chlorine concentrations (0.02 mg/L), oxidation remained limited, with no increase in the carbonyl index, suggesting effective stabilization. At higher chlorination (1 mg/L), oxidation was initially suppressed but accelerated around week 7, suggesting antioxidant depletion followed by material oxidation. Field pipes showed more advanced degradation than laboratory-tested samples, as evidenced by higher carbonyl indices, XPS detection of advanced oxidation compounds (O-C=O), and SEM-observed crack formation. Surface deposits, such as aluminosilicate layers, complicated analysis in some pipe surfaces, but reflected realistic network chemistry. High hardness at the inner surface of the pipe, together with indentation-induced cracks, further indicated embrittlement of the inner surface. In non-chlorinated bioassays, the strongest microbial response was recorded in early migration cycles, indicating the initial release of biodegradable organic carbon from HDPE coupons. In chlorinated batches, TOC increased substantially due to the presence of carbon in the chlorination tablet, but no measurable microbial regrowth was observed, suggesting inhibition by the quenched disinfectant.

Date of Award	2026
Original language	American English
Awarding Institution	HBKU College of Science and Engineering