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Health and water chemistry
Published in Sandy Cairncross, Richard Feachem, Environmental Health Engineering in the Tropics, 2018
Sandy Cairncross, Richard Feachem
Among the many organic compounds found in drinking water, greatest attention has been paid to the trihalomethanes (THMs) – especially chloroform. THMs may be present in concentrations of 1–100 μg/l and occasionally drinking water contains more than 100 μg/l of chloroform. THMs are mainly formed during water treatment by the reaction of chlorine with ‘precursor’ organics in the raw water. THMs are carcinogenic in laboratory animals at high and sustained doses, but there is little concrete evidence of risks to humans associated with low levels of exposure via drinking water. There are many other risk factors for cancer and adverse birth outcomes, and it has been pointed out that a few spoonfuls of some brands of cough linctus provide a chloroform intake greater than a lifetime’s consumption of most drinking waters. The USA, which releases large amounts of THMs into the environment by disinfecting most of its treated wastewater, has adopted a total trihalomethane (TTHM) limit of 80 μg/l in drinking water. Other countries have not followed suit (the WHO guideline for chloroform alone is 300 μg/l) and there is little or no scientific basis for establishing such a low standard at present.
Water and Wastewater
Published in Gary S. Moore, Kathleen A. Bell, Living with the Earth, 2018
Gary S. Moore, Kathleen A. Bell
The most critical step in water treatment, disinfection, should destroy all organisms in the water supply. To ensure proper disinfection, organic matter and other material must be removed prior to disinfection. An important characteristic of an effective disinfectant is that it leaves a residual to prevent re-growth of microorganisms. This residual maintains the purity of the water as it travels to the consumer. Chlorine is the major disinfectant used in United States water systems today. It provides an inexpensive, relatively effective method of killing most waterborne microorganisms and protecting water as it travels through a delivery system. However, chlorine does have some drawbacks. When added to water containing certain organic matter, chlorine can combine with these pollutants to form dangerous disinfectant by-products called trihalomethanes or THM. These compounds have been linked with an incidence of bladder and rectal cancer. Despite the increased risk of cancer from trihalomethanes, chlorinated water is safer than drinking unchlorinated water, due to the threat of waterborne disease. In the many countries throughout the world that lack purified chlorinated water, waterborne disease is a tremendous public health problem. The World Health Organization estimates that several million people die annually worldwide from disease caused by waterborne pathogens. Not chlorinating water to avoid the risks from trihalomethanes would increase the incidence of waterborne disease.80,81
Water Well Rehabilitation
Published in Neil Mansuy, Water Well Rehabilitation, 2017
Another concern with the use of chlorine-based disinfectants is the potential for the formation of chlorinated organic by-products, such as the trihalomethanes (THMs). If you have some of the organic precursors present in the water and you are using chlorine, then you can expect to get THM formation. We have undertaken a number of studies on wells that we have been chlorinating to examine the THM formation potential. The concern was whether THM molecules were being created above the maximum contaminant level (MCL), and the answer was, yes, during the actual period of disinfecting treatment but not after the wells had been flushed. Well rehabilitation treatments have to be looked at as batch treatments. Once that material had been flushed out of the well after treatment there were no THM molecules detected in the subsequent treated water flows. Even after months, there were still no residual THM molecules detected. This would support the probability that THMs are formed after the shock chlorination has been completed but removed when the well was flushed and redeveloped.
Chlorine and ozone disinfection and disinfection byproducts in postharvest food processing facilities: A review
Published in Critical Reviews in Environmental Science and Technology, 2022
Adam M.-A. Simpson, William A. Mitch
Starting in the early 1900s, chlorinating potable water supplies dramatically reduced the incidence of waterborne diseases, such as cholera, listeria, and typhoid (Li & Mitch, 2018). However, in the 1970s, analytical chemists discovered trihalomethanes (THMs) at concentrations of up to 160 µg/L as byproducts of chlorine reactions with natural organic matter (NOM) in drinking water (Li & Mitch, 2018; Rook, 1974). Shortly thereafter, toxicologists and epidemiologists discovered an association between water chlorination and bladder cancer occurrence, with halogenated byproducts suspected to drive the risk (Li & Mitch, 2018). The US EPA has regulatory limits on only 11 DBPs in drinking water: ≤ 80 µg/L for the sum of 4 trihalomethanes (THMs; chloroform, bromodichloromethane, dibromochloromethane, and bromoform), ≤60 µg/L for the sum of 5 haloacetic acids (HAAs; chloroacetic acid, bromoacetic acid, dichloroacetic acid, dibromoacetic acid, and trichloroacetic acid), ≤ 1 mg/L chlorite and ≤ 10 µg/L bromate (USEPA, 2020). California has a 0.8 mg/L Notification Level for chlorate, (California Water Boards, 2020) and a 6 µg/L Maximum Contaminant Level (MCL) for perchlorate in drinking water (California Water Boards, 2007). Much of the research related to DBPs associated with chlorine sanitization of food in postharvest washing facilities has focused on the same small molecule DBPs that have been the focus of drinking water research.
Characterizations of activated carbons and groundwater organic matter adsorption
Published in Journal of Applied Water Engineering and Research, 2023
Mouna Jaouadi, Noureddine Amdouni
Activated carbon (AC) is commonly used as an adsorbent in water treatment due to its low cost and facile operation (Shimabuku et al. 2017). It has been explored as the next-generation adsorbent due to its high surface area, hydrophobicity, porosity, rapid and sorption kinetics (Ateia et al. 2017). Today, the need for enhanced DOM removal can be a driver for installing activated carbon adsorbers. The rate and extent of DOM adsorption in activated carbon filters are difficult to predict (Matsui et al. 2002) because aquatic DOM varies in character spatially across different water sources and temporally within a water source (Laura et al. 2019). The degree of hydrophobicity, the charge distribution, and the ability to form hydrogen bonds with the AC surface affect DOM adsorption. In addition, physically and chemically activated carbon characteristics influence DOM adsorption (Ronan et al. 2020). Furthermore, solution pH, ionic strength, and hardness influence the adsorption of DOM (Shahzad et al. 2020). Vidic and Suidan (1991) studied the effect of dissolved chemical oxygen (DCO) on the adsorption potential of activated carbon for synthetic and natural organic matter. In another study, the efficacy of AC was investigated for the removal of DOM and trihalomethanes (THMs) from the drinking water treated at the Ivedik Water Treatment Plant in Ankara City (Capar and Yetis 2001). Another study examined the removal of DOM from lake water in two pilot-scale adsorbers containing AC with different physical properties (different pore size distributions and grain sizes) (Velten et al. 2011). Modified carbon has also been used for DOM removal. Adsorption of dissolved organic matter from drinking water was examined using two ACs, namely, F400 (coal-based) and Macro (wood-based), after modifications (Dastgheib et al. 2004).