Abstract
Trihalomethanes (THMs) are conditionally carcinogenic compounds formed during chlorine disinfection in water treatment processes around the world. THMs occur especially when source waters are subject to marine influences, high and-or regular precipitation, and elevated levels of organic matter. THMs formation is then rooted in geographic, operational and climatic factors, the relative importance of which can only be derived from large datasets and may change in the future. Ninety three full-scale Scottish water treatment plants (WTPs) were assessed from Jan 2011 to Jan 2013 to identify factors that promote THMs formation. Correlation analysis showed that ambient temperature was the primary THMs formation predictor in potable water (r2 = 0.66, p < 0.05) and water distribution systems (r2 = 0.43, p = 0.04), while dissolved organic carbon (r2 = 0.55, p < 0.001) and chloride (indicating marine influence; r2 = 0.41, p < 0.001) also affected THMs formation. GIS mapping of median THMs levels indicated brominated THMs were most prevalent in coastal areas and on islands. This real-world dataset confirms both geographic and climatic factors are key to THMs formation. If ambient temperatures increase, THMs control will become more challenging, substantiating concerns about the impact of global warming on water quality.
Highlights
The most obvious spatial pattern was for brominated THMs compounds such dibromochloromethane (Fig. 2a), which were primarily found on islands and associated with water treatment plants (WTPs) sites near the coast, which implies a strong influence of marine halides on associated THMs formation in distribution systems
THM formation has been known for many years[37], but most studies on THMs have been based upon local or laboratory assessments, which limits the scope of bigger picture predictions based on multiple real-world observations
It is suspected water quality may decline as climate changes[38], but it is very tenuous to make specific predictions without stronger and more extensive field data that confirm speculation
Summary
Phenolic compounds produced by vegetation decay are released by rainfall and runoff events into surface waters[12,13] Within this context, climate change projections have suggested Scottish temperatures will increase and precipitation will become more variable in the future, increasing microbial and chemical reaction rates, potentially altering DOC levels in surface waters, and bringing new challenges in drinking water treatment[8,14,15,16]. Climate change projections have suggested Scottish temperatures will increase and precipitation will become more variable in the future, increasing microbial and chemical reaction rates, potentially altering DOC levels in surface waters, and bringing new challenges in drinking water treatment[8,14,15,16] Hydrological changes such as water table levels fluctuations, produced by rainfall or drought can increase or decrease in situ DOC levels. The ultimate goal here was to quantify relationships between detected THMs levels, and the seasonality and diversity of DOC across the region, and translate those observations to a deeper understanding how climate change will impact THMs formation and treated water quality in the future
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