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Quantitative assessment of industrial effluents for discharge to sewer
Expanded Title:The major elements that the local authority has for managing industrial wastewater are its wastewater treatment plants for remediation, discharge permits for placing limits on what may be discharged, and a discharge tariff for financing the treatment and for providing a set of incentives and penalties to influence users of the system. An effluent discharge permit consequently is a crucial interface between the local authority and an industry, and the permit system has to carefully balance protection of the general public and the environment against the rights of those working in industry and the promotion of economic activity. The activated sludge process is the most common form of treatment for municipal wastewater in South Africa. In many of South Africa's WWTP's, an industrial wastewater fraction is accepted for treatment with domestic sewage. However, no biological or modelling approach is currently used to estimate impacts and therefore, set limits on discharge. Hence, the conceptual basis of this project was to develop a protocol, involving a combination of laboratory testing and process modelling, which would be able to predict the effect of a range of loads of factory effluent on the operation of the treatment plant receiving its effluent, to inform the process of granting a discharge permit. Due to the sustained high impact of textile effluents on several WWTPs in eThekwini, textile effluents were chosen as the subject of all the investigations. Baseline models were developed for two WWTPs in the eThekwini municipality: Mariannridge and Verulam. Both were selected because they received a significant proportion (approximately 30% by volume) of industrial effluent, and because they experienced significant problems associated with textile effluent, primarily high colour and conductivity. Several series of tests were carried out to establish a methodology for assessing the biodegradability of surfactants using the OUR apparatus. The project faced several challenges: 1) Characterisation of the incoming wastewater proved to be the major difficulty in both investigations. For Mariannridge this was accomplished largely through the use respirometry (oxygen utilisation rate) measurements to fractionate the incoming COD into the categories required for modelling. However, in the case of Verulam, the respirometry methodology did not yield consistent results due to interference. Consequently, a method was developed to estimate the wastewater characteristics based on the flow balance on the WWTPs catchment, using data on the major industrial sources drawn from records kept as part of the municipality’s permit system. 2) Tests showed that the activated sludge process removes azo dyes from wastewater to a small extent. The mechanism for this appears to be physical adsorption onto the sludge, with the adsorptive capacity of actively growing sludge a little higher than for inactive sludge. The adsorption rates are such that equilibrium is attained within approximately 1 hour, which is substantially faster than other processes in the activated sludge process. Consequently an accurate kinetic model of the adsorption process is not necessary. 3) The baseline model developed for Mariannridge could not be used since Dyefin the initial factory to be tested closed. 4) The baseline model developed for a second plant, Verulam could also not be tested due to interference and lack of results from respirometry tests. Attempts to transfer the OUR measurement techniques to municipal staff met with very little success. This was partly due to the problems with the reliability of the technique, but it also had a lot to do with the unavailability of technical staff with the required level of skill, patience and time to devote to such a time-consuming measurement. Thus, although the project was motivated by a perceived need of the municipality to develop a more scientifically defensible basis for setting permit limits, there seems little chance that they would be able to implement such a complex protocol in-house for the foreseeable future. The obvious alternative would be to set up a specialist consultant service, with integrated laboratory and computational capabilities.
Date Published:01/08/2013
Document Type:Research Report
Document Subjects:Wastewater Management - Domestic, Wastewater Management - Sewers
Document Format:Report
Document File Type:pdf
Research Report Type:Standard
WRC Report No:1734/1/13
ISBN No:978-1-4312-0452-6
Authors:Brouckaert C; Mhlanga F; Mashava A
Project No:K5/1734
Organizations:University of KwaZuIu-Natal
Document Size:1 172 KB
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