Treatability of South African surface waters by enhanced coagulation

Abstract

The majority of South African inland surface water sources are  compromised due to a long-standing national policy of mandatory return flows. With renewed emphasis on the removal of organic carbon in the latest SANS 241 water quality standard, many South African water treatment managers may need to consider adoption of enhanced coagulation (EC) in the near future to achieve both turbidity and NOM removal. From the study of 4 South African inland waters, this paper demonstrates that UV254 absorbance provides a more accessible, reliable and rapid way of  monitoring NOM at treatment plant level. This report also provides a  detailed procedure for determining the dosages for EC in terms of UV254 absorbance at jar test level. Using ferric chloride as coagulant, a correlation was established to estimate the coagulant dosage for any desired level of UV254 absorbance removal. This correlation enables a preliminary  assessment of EC as a means of planned NOM removal. Should EC  promise to be a candidate process for NOM removal, it should be verified at jar test level using the proposed procedure.

Keywords: Natural organic matter, enhanced coagulation, ferric chloride, jar test, UV absorbance, modelling