Monitoring natural organic matter and disinfection by-products at different stages in two South African water treatment plants

Bb Mamba,J Haarhoff,Rw Krause,B Matsebula

doi:10.4314/wsa.v35i1.76650

Abstract

Natural organic matter (NOM) is a complex organic material present in natural surface water. NOM can cause problems during water treatment . most notably the formation of toxic disinfection by-products. This study was undertaken in order to assess the effectiveness of some of the water treatment techniques employed by selected water supply companies in South Africa in dealing with NOM. Total organic carbon (TOC) and ultra violet (UV) absorbance at wavelength of 254 nm were measured and used to calculate specific ultra violet absorbance (SUVA), which was used to determine the changes in NOM concentration throughout the water treatment train. Other parameters measured include pH, turbidity, chemical oxygen demand (COD) and conductivity. Water samples were collected from two water treatment plants in South Africa, namely Sedibeng (Balkfontein) and Midvaal. The overall TOC reduction after the water treatment processes was 33% and 30% at Midvaal and Sedibeng, respectively. SUVA values were generally low (<2 ..mg-1.m-1) indicating the presence of aliphatic compounds and less earomaticityf in NOM of the water samples. Water insoluble ƒA-cyclodextrin (ƒA-CD) polyurethanes were then applied to the water to compare TOC reduction in addition to enormalf water treatment processes, and were found to provide up to 19% additional TOC decrease, and UV absorbance reduction was up to 78%. Results obtained using gas chromatography-mass spectrometry (GC-MS) analysis after chlorination, revealed that the water had the potential to form halomethane compounds with chloroform being the most dominant. Again, water-insoluble ƒA-CD polyurethanes were applied to the water as a treatment to remove trihalomethanes (THMs) and were found to efficiently remove up to 95% of THMs formed during the disinfection step. The treatment processes studied have limited ability in dealing with NOM and are not individually effective in NOM removal. Results obtained indicate that the application of ƒA-CD polyurethanes in addition to the water treatment processes may enhance NOM removal in water and significantly reduce the THMs formed.

Highlights

The goal of potable water treatment is primarily to produce drinking water that does not pose any health hazard to humans
It was noted in water samples from Midvaal that there is a slight increase in Total organic carbon (TOC) after treatment, which may be due to biofilm formation in the distribution pipes
There is a reduction in TOC which is used as a measure of Natural organic matter (NOM), the treatment processes have limited ability in dealing with NOM and are not individually effective in NOM removal

Summary

Introduction

The goal of potable water treatment is primarily to produce drinking water that does not pose any health hazard to humans. This study was undertaken to investigate the effectiveness of some of the current water treatment processes currently in use at the Midvaal and Sedibeng water treatment plants in the removal of NOM and related disinfection by-products.

Results

Conclusion