Effects of Intrusion on Disinfection Byproduct Formation in Intermittent Distribution Systems

Abstract

Intermittently operated distribution systems serve over one billion people and may be impacted by the intrusion of contaminated waters carrying disinfection byproduct (DBP) precursors. The impact of intrusion on the formation of 19 DBPs was evaluated in an intermittent water system supplied by deep aquifers in Dhaka, Bangladesh. Untreated piped water samples were collected from residential taps and chlorinated under controlled conditions. Chloride, dissolved organic carbon, and the artificial sweetener sucralose were measured as indicators of intrusion. Most piped water samples had low concentrations of DBPs and indicators; however, a subset had higher levels of DBPs and indicators, suggesting the intrusion of contaminated water into the distribution system, particularly during the rainy season. Piped water samples with evidence of intrusion typically formed higher concentrations of haloacetaldehydes and haloacetonitriles when chlorinated, which greatly increased the calculated cytotoxicity. DBP formation and calculated cytotoxicity in piped water samples impacted by intrusion were comparable to those in piped water samples supplied by horizontal and vertical recharge-impacted groundwaters, yet lower than piped surface waters from other regions of Dhaka. The results demonstrated that intrusion can increase DBP formation in an unpredictable fashion, highlighting the need to sample from many locations in intermittent water systems to accurately evaluate DBP exposure risk.

Disinfection Byproducts in Intermittent Piped Water Supplies

“…Although high concentrations were found in groundwater across samples in both cities (12–1400 μg/L), I-THM concentrations were low in most samples. On the contrary, Furst et al found low (<12 μg/L) bromide concentrations in most water samples tested from Dhaka, Bangladesh. While higher concentrations of Br-DBPs found in the study conducted in India were due to higher concentrations of bromide in source water, the second study that investigated the effect of intrusion did not find significant effects on bromide or Br-DBP concentrations.…”

“…Furst et al are the only publications, to the best of our knowledge, reporting measurements of bromide and iodide concentrations and Brand I-DBPs in IWS systems. 32,33 Furst et al 32 found higher bromide concentrations in groundwater in two cities with IWS, Jaipur and Jodhpur, India, and also higher bromide concentrations between the surface water source of Jaipur (140 μg/L) compared to Jodhpur (10 μg/L), which led to higher concentrations of brominated haloacetonitriles that contributed the majority of the toxic potency-weighted DBP concentrations and higher bromine substitution factors. Although high concentrations were found in groundwater across samples in both cities (12−1400 μg/L), I-THM concentrations were low in most samples.…”

“…Intrusion from raw sewage and agricultural runoff may introduce other organics, such as nitrogenous organic matter, that may increase nutrient loading and shift the speciation of DBPs within the DWDN toward greater concentrations of N-DBPs. 33 N-DBPs were first discovered in the early 1980s when HANs, a significant group of N-DBPs, were detected in chlorinated source waters. 84 This class of DBPs is of particular interest due to their greater health risk, as HANs, HAMs, and halonitromethanes (HNMs) have been found to be far more cytotoxic and genotoxic than U.S.-regulated THMs and HAAs.…”

“…Overall, DBP concentrations, characterized by TTHM concentrations, have been highly variable across studies, and trends are not well established (Table ). However, the most recent publications by Furst et al , provide a great beginning for understanding the effects of IWS on DBPs in drinking water.…”

“…Intrusion from raw sewage and agricultural runoff may introduce other organics, such as nitrogenous organic matter, that may increase nutrient loading and shift the speciation of DBPs within the DWDN toward greater concentrations of N-DBPs . N-DBPs were first discovered in the early 1980s when HANs, a significant group of N-DBPs, were detected in chlorinated source waters .…”