Chlorination by-products formation in a drinking water distribution system treated by ultrafiltration associated with pre-ozonation or coagulation/flocculation

Abstract

One of the main drawbacks of ultrafiltration (UF) membranes is their limited capacity to remove organic matter, which can favour the biofilm development in drinking water distribution systems (DWDS) and the deterioration of water quality, mainly due to the formation of disinfection by-products. This was conducted to assess the evolution of the water quality in an experimental DWDS fed with water treated by spiral-wound-polyvinylidene-fluoride UF membranes. Two different systems were compared: a coagulation-flocculation-UF and an ozonation-UF. Comparison was made with respect to the occurrence of trihalomethanes (THMs) and haloacetic acids (HAAs) as well as biofilm development in the DWDS, along with the evolution of pH, DOC, UV254, turbidity and total aerobic bacteria. During both stages, the surface of the DWDS was colonized by bacteria, and water quality deteriorated, although to a lesser degree when the coagulation-flocculation-UF was applied. The use of ozone caused a higher increase in the formation of both THMs and HAAs than coagulation-flocculation, with chloroform as the only THM detected and dichloroacetic acid as the main HAA (90%) for both stages. Mean THM concentrations of 177.7 µg L-1 and 85.0 µg L-1 of HAAs were registered working with the ozonation-UF, which throws considerable doubt on the potability of the water in DWDS. In addition to the treatment, water temperature was the most influential variable on the formation of HAAs and THMs, whereas DOC, UV254 or specific UV absorbance proved not to be useful parameters for assessing the possible formation of THMs or HAAS in DWDS