Abstract
Natural organic matter (NOM) represents a range of heterogeneous hydrophobic and hydrophilic components naturally occurring in the water source and, due to the fact that they can act as precursors for the disinfection, by-products may have a considerable impact on drinking water quality. Coagulation–flocculation (C/F) is among the most applied processes for NOM removal from water sources (especially rivers). In this study, C/F efficiency for a river water supply was investigated in cold and warm conditions, by varying the coagulant dose and mixing conditions. In this study, polyhydroxy aluminum chloride PAX XL 60, and polyacrylamide FloPam AN 910 SEP were used as coagulant and flocculant, respectively. Multiple water quality indicators were determined, such as turbidity, chemical oxygen demand (COD), dissolved organic carbon (DOC), and residual aluminum concentration. Some unconventional parameters relevant for NOM removal were also considered, like absorbance at 254 nm (A254), at 280 nm (A280), and at 365 nm (A365), as well as the ratios A254/DOC, A254/280, and A254/A365. After coagulation–flocculation, turbidity was completely removed in all the studied conditions. The DOC content was reduced by up to 22.65% at a low temperature and by up to 31.81% at a high temperature. After the addition of polyelectrolyte in cold conditions, the efficiency in terms of A254 increased by up to 37.4%, while the specific absorbance decreased. The high molecular weight NOM increased after C/F, based on the A254/A365 ratio. Chemometric analysis was employed in order to determine the effect of the coagulant dose on the process efficiency. The optimum coagulation–flocculation conditions were corroborated by means of the principal component analysis.
Highlights
Natural organic matter (NOM) is present in most of the surface water supplies, along with suspended particles, colloids, and pathogens
The presence of natural organic matter in sources adequate for drinking water treatment, mainly humic acid and fulvic acid, contributes to the formation of disinfection by-products (DBPs), when water is treated with a disinfecting agent, such as chlorine or chloramine, which leads to the potential presence of carcinogenic compounds in conventionally treated waters
This study presents a series of experiments obtained on a laboratory scale set up for the coagulation–flocculation of surface water from the Prut River, which is the drinking water supply for a city in northern Romania
Summary
Natural organic matter (NOM) is present in most of the surface water supplies, along with suspended particles, colloids, and pathogens. The presence of natural organic matter in sources adequate for drinking water treatment, mainly humic acid and fulvic acid, contributes to the formation of disinfection by-products (DBPs), when water is treated with a disinfecting agent, such as chlorine or chloramine, which leads to the potential presence of carcinogenic compounds in conventionally treated waters (involving chlorination as the final stage of raw water treatment). These DBPs in drinking water, including aliphatic halogenated trihalomethanes (THMs), haloacetonitriles, and haloacetic acids (HAAs), have been found to be toxic and associated with many forms of cancer, endocrine disorders, or other diseases [6,7]. Due to the public concerns regarding the potential health effects of DBPs, the European Union (EU) regulated
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