Evaluation of mass-transfer coefficient of free fall--cascade-aerator.

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.