Ecological and economic aspects of treating vegetable oil industrial effluent at Darvill Wastewater Works in Pietermaritzburg.

Abstract

The dissertation analyses the economic and ecological aspects of Darvill Waste Water Works (WWW) through key indicators from Sustainable Development Records (SDR). The SDR study identifies disturbances caused by large concentrations of soap, oil and grease (SaG), therefore a framework of proposed solutions to dealing with these problems has also been investigated. The first component of the study highlights the importance of adequate indicators. Key indicators provide important information that is useful to management and policy makers. The SDR used to analyse the DarvillWWW in Pietermaritzburg provides relevant information for the management of Darvill WWW and Umgeni Water (UW), the City Council and the Department of Water Affairs and Forestry (DWAF). According to the SDR model the Works is identified as a service providing social institution. The operation of this institution affects the community of Pietermaritzburg as well as the surrounding natural environment. SDR uses the key indicators of effectiveness, Thrift and Margin to analyse the economic and ecological impacts of the service provided.The study incorporates relevant data for Darvill WWW during 1993- 1996. Effectiveness measures the degree of compliance with national water quality standards as set out by the DWAF. Compliance of the following variables, E.coli, Chlorine, Soluble Reactive Phosphate (SRP), Total Suspended Solids (TSS), Conductivity, Chemical Oxygen Demand (COD) and Ammonia were investigated. These variables produce varying trends. Increasing compliance is linked to improved plant efficiency while decreasing compliance is linked to the poor quality of industrial effluent. Industrial effluent containing large concentrations of SOG is a particular problem. Thrift measures the costs of operating the Works in terms of energy, chemicals, labour and capital. Overall financial, energy and labour thrift declined while chemical thrift increased. Increasing chemical thrift is due to the reduced consumption of chemicals as a result of a greater reliance on the process of biological phosphate removal. Decreasing thrift is related to increased costs of capital, energy and labour due to the deteriorating quality of vegetable oil effluent. Margin measures the deviation of non-complying samples from water quality standards. Analysis of the data produced varying trends. The following variables were analysed, E.coli, Chlorine, SRP, TSS, Conductivity, COD and Ammonia. Marginal difference is studied in an attempt to analyse those samples which do not comply with national standards. Deteriorating quality of industrial effiuent seems to be the reason for deviation from the standards. Chemical margin was also studied for the period between 1993-1996. Chemical margin is a comparison between the value of sludge produced and the cost of chemicals used to produce the sludge. The SDR study highlights deteriorating quality of industrial effluent as a cause for concern to Darvill WWW. Proposed management options are investigated to provide a workable solution. The second part of the study investigates alternate options for handling wet industrial effluent from the vegetable oil industries. These industries were identified as the source of large concentrations of SOG that were entering the Works which impacts negatively on the operational capacity, thereby increasing operating costs and decreasing the quality of the service provided. Vegetable oil industries were found guilty of discharging industrial effluent that did not meet the City standards into the sewers, they were also charged with illegal dumping into rivers. The study identified the interested and affected parties and alternate solutions were proposed to the problems. Interested and affected parties include UW, Pietermaritzburg City Council, DWAF. Some of the aspects that were investigated include the local industrial tariff, the drainage By-laws, national legislation, the "polluter pays" principle and the principle of pollution prevention. Economic incentives using economic instruments were reviewed. These include ecotaxes such as marketable/tradable permits and pollution charges. These instruments may allow for more equitable charges thereby promoting the "polluter pays" principle. The use of these instruments may be able to achieve a workable solution but further investigations are necessary. SDR analysis indicates that Darvill WWW seems to be effectively treating wastewater but operating costs are increasing in order to achieve compliance. These costs are being unfairly borne by the City ratepayers and UW and a more equitable situation is necessary.