The effect of the molecular mass of the organic matter in raw water on the formation of disinfection by-products

This research used an ultra-membrane filtration system to divide raw water into four different organic groups with different molecular masses. The effects of each organic group on the quantity of disinfection by-products formed after a reaction with chlorine dioxide was investigated. The experimental results show that the four organic groups of different molecular masses were: 10 kD<average molecular mass (AMM)<0.45 µm; 5 kD<AMM<10 kD, 1 kD<AMM<5 kD, and AMM<1 kD. Their distribution proportions were 10.8%, 46.8%, 13.3% and 29.1%, respectively. In the reactivity between the organic substances and chlorine dioxide, it was discovered that the reaction breaks down the organic substance large molecules into smaller molecules and cannot directly mineralize the large organic molecules into inorganic carbon. In comparison, the small organic substance molecules (5–1 kD, AMM<1 kD) contributed most disinfection by-products per unit organic carbon (THMs/DOC, THAAs/DOC).