First derivative UV spectra of surface water as a monitor of chlorination in drinking water treatment.

V Zitko

doi:10.1100/tsw.2001.13

Abstract

Many countries require the presence of free chlorine at about 0.1 mg/l in their drinking water supplies. For various reasons, such as cast-iron pipes or long residence times in the distribution system, free chlorine may decrease below detection limits. In such cases it is important to know whether or not the water was chlorinated or if nonchlorinated water entered the system by accident. Changes in UV spectra of natural organic matter in lakewater were used to assess qualitatively the degree of chlorination in the treatment to produce drinking water. The changes were more obvious in the first derivative spectra. In lakewater, the derivative spectra have a maximum at about 280 nm. This maximum shifts to longer wavelengths by up to 10 nm, decreases, and eventually disappears with an increasing dose of chlorine. The water treatment system was monitored by this technique for over 1 year and changes in the UV spectra of water samples were compared with experimental samples treated with known amounts of chlorine. The changes of the UV spectra with the concentration of added chlorine are presented. On several occasions, water, which received very little or no chlorination, may have entered the drinking water system. The results show that first derivative spectra are potentially a tool to determine, in the absence of residual chlorine, whether or not surface water was chlorinated during the treatment to produce potable water.

Highlights

Chlorination is a widely used disinfection process in the production of drinking water
This paper shows that changes in the UV spectra of natural organic matter (NOM, dissolved organic carbon, fulvic acid, humic acid) present in surface water may be used for this purpose
Since no free chlorine was detectable in the large-volume users system, and, occasionally, in the town system, it was important, for reasons of public health, to determine whether or not the water was chlorinated at the lake

Summary

INTRODUCTION

Chlorination is a widely used disinfection process in the production of drinking water. It may be that the residual chlorine was decomposed in the distribution system or that, by accident, the water was not chlorinated at all The latter may result in a serious public health problem. It is important, in the absence of residual chlorine, to be able to determine the chlorination history of drinking water. The decrease in UV absorbance is correlated to the formation of organic halogen compounds and disinfection by-products This correlation is improved by determining the absorbance difference between original and chlorinated water samples[5]. Since no free chlorine was detectable in the large-volume users system, and, occasionally, in the town system, it was important, for reasons of public health, to determine whether or not the water was chlorinated at the lake.

MATERIALS AND METHODS

RESULTS AND DISCUSSION

CONCLUSIONS