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The main goal in using chlorine as water disinfectant is to protect the water in the distribution systems against microbial contamination and to prevent and control re-growth of microorganisms in the water distribution system. Organics in water have the potential to generate harmful disinfection by-products (DBPs) such as trihalomethanes (THMs) as a result of their reaction with chlorine. DBPs are increasingly recognized as cancerous agents. Residual chlorine concentration, temperature and pH are the major factors that influence the rate and degree of THMs formation. Trihalomethanes formation potential (TFP) is very useful test to assess the level of the formation of trihalomethanes. Seasonal variations of TFP of post chlorinated treated water were investigated at six water treatment plants (WTPs) in Delhi City (India).The post chlorinated treated water samples from Bhagirathi, Sonia Vihar, Wazirabad, Nangloi, Okhla, and Haiderpur WTPs were collected just at the outlet before water supply to the consumers. The investigation was based on an intensive bi-monthly sampling program, undertaken from May 2007 to March 2008. Correlation among TFP, residual chlorine, temperature and pH, and their variation throughout the year is also discussed in this paper.

The mass-transfer coefficient of a free-fall cascade-aerator unit of 15 million litres per day was evaluated for its efficiency in the removal of a class of volatile organics, the trihalomethanes (THMs). These compounds are carcinogenic and occur as a result of chlorination of natural waters. Due to the volatile nature of the THMs, the efficiency of aeration as a potential technique for their removal has been studied. The principle behind aeration is gas-transfer, according to which the gas-liquid interface is hypothesized to consist of a gas and liquid film through which gas is transferred by molecular diffusion until equilibrium is attained. The overall mass transfer coefficient (K(L)) of the aerator considering oxygen as the reference compound, was found to be 29.3 hr(-1) for THMs.