Protocol for the quantitative assessment of industrial effluents for discharge permitting (WRC K5/1734)

Funded by: Water Research Commission
April 2007 – November 2012

Partner organisations: University of Ghent; eThekwini Water and Sanitation, University of Cape Town; Durban University of Technology; Sasol

Project description
The project started in 2007 and was originally planned to end in 2010, but was twice extended in 2011 and 2012. 2007 was used to conduct a survey of South African municipal systems for regulating the discharge of industrial effluent to sewers. The results of this survey were presented at a workshop for municipal wastewater treatment officers in November 2007. One of the outcomes of the workshop was to establish support for the methodology proposed for the rest of the project.
The broad conceptual outline of the methodology was:
  • To use textile effluents discharged to wastewater treatment plants (WWTPs) in eThekwini as case studies.
  • To develop laboratory techniques for characterizing effluents in terms of their impact of wastewater treatment processes.
  • To set up simulation models of the wastewater treatment processes which are capable of assessing the risk of accepting an industrial effluent for treatment.
  • To test the applicability model based risk assessment by participating in a permit evaluation process conducted by the eThekwini Pollution and Environment Department.
According to this concept, a baseline model of the WWTP would be set up and calibrated to represent the average conditions of the sewer catchment. This obviously involved characterisation of the average wastewater received by the WWTP. Factory effluent would be characterised in a similar way. The risk assessment would then consist of simulating WWTP operation for combinations of the factory effluent and the average wastewater, and predicting the quality of the treated wastewater.
The WWTP initially selected for the study was the Mariannridge plant, which in 2008 experienced significant problems with textile effluent from the Dyefin factory. A baseline for the Mariannridge WWTP was set up and calibrated in the MScEng project of Farai Mhlanga. However, in 2009 the Dyefin factory closed down and relocated to another catchment, which removed the textile effluent from the wastewater treated at Mariannridge.

Meanwhile, laboratory methods for characterising textile effluents were being investigated in the laboratory. The three key problematic constituents that were identified were residual dyes (colour), dissolved salts (conductivity) and surfactants (biodegradable COD and foaming). Of these, conductivity is not treated at all in biological processes, and can only be controlled within the textile factory. Dyes are also resistant to biodegradation, however they are partially removed by adsorbtion onto the activated sludge biomass. Surfactants used in textile processing are generally almost completely biodegradable, but their degradation rates may be different to normal sewage components.
In 2008, a study was undertaken by David Mzulwini, an eThekwini process engineer who registered for an MScEng, on the effectiveness of the municipality’s permitting system. Unfortunately he took ill and died before completing his degree, but he had come to the conclusion that the effluent discharge permits were not protecting the WWTPs as they should, not because of the way they were framed, but because their provisions were not being adequately enforced.

Since the Dyefin / Mariannridge WWTP system was no longer available for study, it was decided in 2009 to turn to the JMV Textiles / Verulam WWTP system. A new treatment plant at Verulam was commissioned towards the end of 2009, which had been provided with much more comprehensive an instrumentation and control system that is much more advanced that most other WWTPs in South Africa. A study at JMV Textiles in 2009 resulted in a mass-balance model of the factory which predicted the quantity and composition of effluent from their production schedule.

The development of a baseline model for the Verulam WWTP was hampered by major difficulties in characterising the wastewater that it receives. The MScEng student who was investigating the use of respirometry for characterising the biogradabable fractions left the programme without completing. The first extension of the project, at the end of 2010, was requested to allow more time to solve the measurement problems. These difficulties had not been anticipated, because the respirometry technique has been extensive used by the University of Cape Town Water Research Group. There were indications that the presence of some industrial components might be interfering with the measurements, but, without a student devoted to the topic, it was not easy to establish exactly where the problem lay.