Estudo de identificação e quantificação de trialometanos em água de abastecimento

Abstract

Chlorine has been often used as the main oxidant for organic material, as well as for deactivating patogenic organisms that live under natural waters. The organic material found in superficial manancials is also known as humic substance. These substances, when reacting with chlorine or one of its derived products (in the preoxidation or desinfection phase), produce halogenated organic compounds, which are potentially cancerigenous, such as the trihalomethanes (THMs). Quantitatively, most of the resulted trihalomethanes structure are cloroform, bromodichloromethane, dibromochloromethane and bromoform. The sum of these four compounds are called total trihalomethanes. Usually, the reaction doesn’t produce these compounds in natural conditions, and it could take several days until they arrive in the water supply system. In the water treatment public supplying, the chlorine pre-oxidation phase is the one that mostly contribute to these compounds formation. This research propose the use of gas cromatography with headspace-trap (CG/HS-trap) for determining the total THM and their formation potential after the water treatment public supplying. This technique eliminates the need of sample extraction. Natural waters were used, with samples from two river with differents apparent color and absorbance 254nm. For determining the oxidant dosagem with respect to the contact time, we used a technique based on calcium hypochlorite and potassium permanganate. We also evaluated of the influence of the conventional water treatment, when the pre-oxidation phase uses the studied oxidants. Experimentally, we reduced the THM formation in 98% in one sample and 50% in the other one when the water was treated with potassium permanganate instead of chorine in the pre-oxidation phase. The same ocurred for the THM formation potential.