Comparisons of disinfection byproducts (DBPs) formation from natural organic matter (NOM) and biofilm

It is well known that chlorine can inactivate most of the microorganisms in water, and the residual chlorine in water distribution system can prevent the microorganisms regrowth and biofilm formation. However, with the increase of travel distance and residence time in the distribution systems, the residual chlorine will decrease and microorganisms may regrowth and biofilm will be formed, which will deteriorate the water quality. Most research related to disinfection byproducts (DBPs) focused on the reactions between the disinfectant and natural organic matters (NOMs), only little information available concerning the reactions between disinfectants and microorganisms and biofilm. This study intend to assess the DBPs formation from biofilms, samples were collected from the water distribution systems of Tai-Hu Water Treatment Plant and a biofilm culture device installed in Tai-Hu Water Treatment Plant to assess the characteristics of DBPs formation from biofilms.
Results showed that there is not enough residual chlorine remained in water samples collected from distribution systems. With the increased water travel distance in the distribution systems, the concentration of haloacetic acids (HAAs) decreased; which means that there were microorganism regrowth since HAAs are biodegradable. The results were the same for tap water samples flew through the household water storage tanks. After biofilm was cultured for three months, the results showed that the heterotrophic microorganisms increased with the increased contact time. Excitation-Emission Matrix (EEMs) analysis of samples from biofilm showed that the organic matters from biofilm were mostly aromatic proteins, and the organic matters from distribution system water were mainly humic acid and fulvic acid. Results of the DBPs formation potential tests showed that the DBPs produced from reactions between chlorine and biofilms were trihalomethanes (THMs), which is not consistent with other studies. A possible explanation is that there are many other organic matters in the biofilms and different microorganisms may produce different extracellularpolymeric substances (EPS), which lead to formation of different DBPs.