Page 93 - EER-2-3

Explora: Environment
and Resource Comparative analysis of THMs and THAAs in water distribution media

activity in the water supply network. A free chlorine (PP) > polyvinyl chloride. In another study, Chen et al.
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residual of up to 0.2 mg/L is typically maintained in the found that biofilm accumulation in pipes used for 2 years
distribution system, as it helps minimize the risk of further increased THM and THAA concentrations to 59.5–
contamination. However, chlorine concentration tends to 123 µg/L and 35.1–51.6 µg/L, respectively—significantly
decline over time due to its dissolution behavior. These higher than levels in new pipes.
findings by Al-Jasser are fully supported by the findings Volatile chlorinated hydrocarbons, which are known
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of Clark and Wymer; however, Jahin et al. noted that carcinogens, have been regulated by the United States
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higher chlorine dosages are commonly applied worldwide (US) Environmental Protection Agency (EPA) at a
to ensure effective disinfection. 3-5 maximum contaminant level of 0.005 mg/L. Even
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Dissolved organic matter is a complex natural component though chlorination is the most widely used technique
found in water, often introduced through anthropogenic for disinfecting water, it has some disadvantages. Long-
activities, and is recognized as a primary contributor to term exposure can lead to cancer due to the formation of
the formation of chlorination disinfection byproducts DPBs, which can also negatively affect the kidney, liver,
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(DBPs). Substances such as organic impurities, ammonia and contribute to other health issues. Moreover, the
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compounds, and residual metallic ions (e.g., ferrous ions, factors influencing DBPs formation in WDS (e.g., pipe
magnesium) are prominent components that interact with materials, deposits, and biofilms) are not isolated but act
chlorine and are consumed during the reaction. 3 synergistically to promote DBP formation. 11
Kali et al. found that the most prevalent DBP groups Different countries report varying average
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are trihalomethanes (THMs) and trihaloacetic acids concentrations of THMs, ranging from 0 to 1000 mg/L. For
(THAAs), which are formed when chloramine and instance, the average THM concentrations in treated water
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chlorine react with organic and inorganic matter. In samples in Nigeria range from 0 to 95 mg/L. Similarly,
addition, Maul et al. and Rossman et al. observed a rapid up to 18 mg/L of DBPs were detected in finished water
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decrease in both free and total chlorine residuals in the and up to 22 mg/L of DBPs in distribution systems in the
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water distribution system (WDS) as hydraulic residence US. In China, the average concentrations of THMs and
time increased. Due to limitations in chlorine persistence HAAs throughout the treatment process were 19.9 mg/L
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within the WDS, secondary chlorination is often required and 3.4 mg/L, respectively. These data indicate that DBP
to maintain effective sterilization and disinfection of concentrations in WDS are spatially variable. 21
drinking water. However, this secondary chlorination In the Chinese WDS, the concentration of THMs ranged
can further react with natural organic matter (NOM) from 3.67 µg/L to 30.30 µg/L, while tribromomethane
and microbial contaminants, leading to the formation of concentrations were below 3.15 µg/L. The average
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additional DBPs during water delivery. 10 total THM concentration in China was approximately
WDSs play a crucial role in the secondary formation 16.6 µg/L, which is lower than that reported in the US and
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of DBPs, potentially increasing the risk of excessive DBP Saudi Arabia (33.6 µg/L). HAAs in China ranged from
accumulation during water transport. The complex 0.83 to 18.8 µg/L in WDS water, with dichloroacetic acid
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environment within WDS, including residual chlorine and trichloroacetic acid showing similar concentration
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and organic matter, influences further DBP formation. ranges in WDS samples.
A study by Charisiadis et al. found a significant positive In addition, Amjad et al. found that higher levels of
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correlation between hydraulic residence time and THM total THMs were reported in Islamabad compared to
levels in the WDS. Rawalpindi, possibly due to Islamabad’s reliance on surface
water, whereas Rawalpindi residents primarily access
Different regions use varying pipe materials based on
supply conditions and regulatory standards. Cast iron, groundwater through tube wells, open wells, or pressure
pumps. This suggests that groundwater, which contains
the most widely used material, is prone to corrosion, lower concentrations of NOM, may lead to reduced DBP
releasing iron ions that accelerate DBP formation. In formation. In densely populated Pakistan, with an average
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comparison, galvanized steel pipes exhibit a higher rate life expectancy of 70 years, cancer cases related to THM
of chlorine decay. Hydraulic shocks in plastic pipes can exposure are reportedly increasing. Karachi, the largest
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lead to microplastic release, which may contribute to DBP metropolitan city with approximately 18 million residents,
formation, further deteriorating water quality. 14
is projected to have a high burden of cancer cases linked
He et al. reported that the rate of haloacetic acid to DBP exposure. However, according to Pejman et al.,
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formation among four plastic pipe materials followed the both Rawalpindi and Islamabad have still reported fewer
order: high-density polyethylene (HDPE) > polypropylene cases than Tehran.
Volume 2 Issue 3 (2025) 2 doi: 10.36922/EER025240047