Xanthopoulou, NJ; Papagianni, MV; Papaioannou, A; Haralambidou, A
Proceedings of the 9th International Conference on Environmental Science and Technology, Vol A - Oral Presentations, Pts A and B
Chlorination has been the most widely used technology for the disinfection of drinking water around the world. The main purpose for the disinfection of drinking water is to protect it against microbial contamination in the distribution systems and to prevent or at least control re-growth of microorganisms in the pipelines.
A major disadvantage of chlorination is the formation of a wide variety of halogenated compounds from natural organic matter.(1,2) Some of these by-products, namely trihalomethanes (CHCl3, CHBrCl2, CHBr2Cl and CHBr3), 1,2-dichloroethane, trichloro- and tetrachloro-ethene have diverse negative effects on human health, including toxicological, mutagenic and carcinogenic effects, as well as induction of congenital malformations and retarded fetal growth.(3) Current regulations in Europe demand a target of 100 mu g L-1 for trihalomethanes (THMs), 3 mu g L-1 for 1,2-dichloroethane, 10 mu g L-1 for trichloro- and tetrachloroethene. Apart from these compounds, European regulations set a limit of 1 mu g L-1 for benzene and include all the pre-mentioned compounds in the category of volatile organic compounds (VOCs).
Since September 2003, the city of Thessaloniki and its suburbs are gradually supplied with drinking water from the Thessaloniki Water Treatment Plant (TWTP), which takes raw water from the river Aliakmonas. The treatment process in the plant includes: preozonation, pH adjustment, coagulation with aluminum sulfate, flocculation, sedimentation, rapid sand filtration, ozonation, activated carbon (GAC) filtration, chlorination and pH adjustment to pHs. The TWTP's capacity is 150.000 m(3)/day.
The fact that Thessaloniki is partly supplied with surface water from Aliakmonas river, created much concern among consumers regarding the levels of THMs and VOCs formed by chlorination. A year ago, a regular monitoring program started at the TWTP, during which, THMs and VOCs included in the European guidelines were determined in the finished drinking water, approximately 20 min after chlorination as well as in the outlet of the storage tank. At the same time, parameters such as pH, temperature, chlorine demand, total organic carbon (TOC) and contact time (t(R)) were monitored.
None of the VOCs mentioned above were detected in the samples during the period of February 2004-February 2005 except for THMs. The relatively low levels of THMs were attributed to the steadily low TOC levels of the finished water which were about 0,9-1 mgL(-1). THM levels ranged from 0,16 to 12,92 mu g L-1. These levels were correlated with all the parameters measured and showed that contact time and temperature had the most evident effect.