Challenges in the potable water industry due to changes in source water quality: case study of Midvaal Water Company, South Africa

Challenges in the potable water industry due to changes in source water quality: case study of Midvaal Water Company, South Africa Shalene Janse van Rensburg1, Sandra Barnard2* and Marina Krüger1 1 Midvaal Water Company, Farm Buffelsfontein 443 IP, District Klerksdorp, 2570, South Africa Unit for Environmental Sciences and Management, North-West University, Potchefstroom 2520, South Africa 2 ABSTRACT Midvaal Water Company treats hypertrophic water abstracted from the Vaal River to supply bulk wholesome potable water to their consumers in compliance with the South African National Standard (SANS) 241:2015 for drinking water. The facility incorporates conventional and advanced treatment processes. The aims of the study were to identify how the water treatment processes of the plant have changed over time in response to the varying water quality of the Vaal River, and to consider both current and future obstacles as well as possible solutions regarding water quality and treatment. Oxidation steps such as pre-chlorination, potassium permanganate addition, pre-ozonation and intermediate ozonation have either been applied in the past or are still operational. The dissolved air flotation plant accounts for almost 70% of total chlorophyll removal and the significance of this process was confirmed during a brief maintenance shutdown during 2015. Total chlorophyll concentrations of the source water have increased extensively since 1984, while turbidity levels have remained fairly constant but with spikes at times. The facility suffers from severe taste and odour episodes during warm periods due to the presence of methylisoborneol (MIB), released by Cyanophyceae, in the Vaal River. Concentrations of > 300 ng/L MIB have been recorded, whereas the odour threshold concentration for MIB ranges from 4 ng/L to 20 ng/L. The additional application of activated carbon to alleviate taste and odour problems has to be weighed against the cost implications for consumers, the correct type to be purchased for the organic molecules to be adsorbed, the interference of natural organic matter, and the formation of additional sludge mass, as well as the intensity and duration of taste and odour events. Midvaal remains a bulk potable water supplier and therefore has to consider the socio-economic status of their consumers where water pricing is concerned. The study ultimately emphasized the intrinsic value of protecting water resources. Keywords: oxidation processes, dissolved air flotation, chlorophyll a, taste and odour INTRODUCTION The erstwhile Western Transvaal Regional Water Company was established in 1954 to address the drinking water needs of various mining companies at the time. The company is situated in the North West Province of South Africa on the banks of the Middle Vaal River, close to the small town of Stilfontein. The name was changed to Midvaal Water Company in 1998, with the new name derived from its location. Midvaal Water Company supplies bulk potable water to the local municipality, Vierfontein, and the mining industry in the surrounding area. The local municipality is the City of Matlosana Municipality which serves the towns of Klerksdorp, Orkney, Stilfontein and Hartbeesfontein (the KOSH area), which includes approximately 500 000 consumers. Vierfontein, in the Free State Province, has about 1 500 consumers. Anglogold Ashanti represents the majority of the mining industry in the area and is also responsible for the company Mine Waste Solutions which deals with tailing storage facilities reclamation. The 1 120 km long Vaal River originates in the Mpumalanga Province of South Africa and is both heavily used and polluted by the time it passes the treatment works close to Stilfontein. The hypertrophic water from the Vaal River serves as their only water source and is purified by means of various conventional (coagulation and flocculation, sedimentation, filtration and disinfection) and advanced treatment processes (dissolved air flotation (DAF) and ozonation) prior to distribution. * To whom all correspondence should be addressed. ☎ +27 18 299-2508; e-mail: Received 8 December 2015; accepted in revised form 20 September 2016 http://dx.doi.org/10.4314/wsa.v42i4.14 Available on website http://www.wrc.org.za ISSN 1816-7950 (Online) = Water SA Vol. 42 No. 4 October 2016 Published under a Creative Commons Attribution Licence THe first aim of this study was to identify the prior objectives, criteria and indicators of water treatment for Midvaal Water Company, and to show how the water treatment processes of the plant have changed over time to adapt to the varying water quality of the Vaal River. The second aim was to consider both current and future concerns and possible solutions regarding water quality and treatment. METHODS The study site is situated 14 km from Stilfontein, at 26°55’59.3” S and 26°47’51.8” E. Vaal River water quality data were available from 1984 and operational data were available from 2010. Water treatment at Midvaal Water Company currently consists of the following processes which have been implemented since 2007 (see Fig. 1 and Table 1): 1. Abstraction from source (Middle Vaal River) at intake tower 2. Pre-ozonation 3. Primary addition of water treatment chemicals for coagulation and flocculation. A combination of all or some of the following chemicals are used in this process depending on the water quality: lime, ferric chloride, polyelectrolyte and aluminium sulphate 4. Dissolved air flotation (DAF) 5. Intermediate ozonation 6. Secondary addition of water treatment chemicals (optional). A combination of all or some of the following chemicals are 633 used in this process depending on the water quality: lime, ferric chloride, polyelectrolyte, aluminium sulphate and powdered activated carbon (PAC) • • 7. Sedimentation • ph Electrical conductivity Turbidity 8. Filtration • Total chlorophyll • Chlorophyll-a • Manganese • Iron • • Colour Nitrate and nitrite Orthophosphate 9. Disinfection by means of chlorine gas 10. Pump station for distribution of the final water to 11 reservoirs in the Klerksdorp, Orkney, Stilfontein and Hartbeesfontein (KOSH) area and Vierfontein The following analytical activities were performed by Midvaal Water Company Scientific Services, which was established in the 1970s and has been an accredited SANAS Testing Laboratory since 2002 based on ISO 17025.The source water database dates back to 1984. Operational data have been captured on the Laboratory Information Management System (LIMS) since 2010: • Determined with an electrode since 1984 Determined with an electrode since 1984 Determined with a turbidity meter since 1984 Determined by means of the Sartory (Swanepoel et al., 2008) extraction method since 1984 Determined be means of an in-house extraction method since 2006 Determined since 1984 by means of atomic absorption spectros copy and inductively coupled plasma optical emission spectroscopy Determined sin (...truncated)