K52221 - WWTP modelling to support the Green Drop programme

K5/2221 - WWTP modelling to support the Green Drop programme

Funded by: Water Research Commission

April 2013 – March 2016

Partner organisations: eThekwini Water and Sanitation; Umgeni Water; University of Cape Town

Project description

The Pollution Research Group, in collaboration with the Civil Engineering Department at the University of Cape Town, is developing a model for simulating wastewater treatment processes in order to support the national Green Drop programme in its efforts to improve the standard of wastewater treatment in South Africa. The conventional way of assessing process-performance employs a combination of general discharge standards and historical records for the particular plant, according to a 'continuous improvement' principle. The use of modelling offers the possibility of supplementing this relativistic approach by providing performance criteria that have an absolute basis. Furthermore, process models reflect a deeper understanding of the process than is needed for routine operation and compliance monitoring, and the discipline of constructing a model almost always reveals aspects of the process which were not previously understood. Models provide a convenient and inexpensive platform for exploring different operating strategies or design improvements, which should greatly facilitate the search for continuous improvements.

A series of WRC projects has led to the development of steady-state and dynamic WWTP models at UCT and more recently with the collaboration of UKZN. However, these models have been based on data from laboratory equipment, and have not yet been applied to full scale plants. WWTP modelling has not been put into practice to any significant extent by South African municipalities. Recently EWS and Umgeni Water decided that it was necessary to develop modelling expertise to enhance their competence in WWTP design, control and optimisation. Both organisations experience considerable difficulties at some of their WWTPs arising from the presence of significant loads of industrial effluents, and there are frequently questions as to whether poor treated water quality is due to industrial components in the wastewater or to deficiencies in the treatment processes. To build their expertise, EWS and Umgeni Water have purchased the WEST modelling software, but they find it difficult to allocate the necessary skilled manpower resources and analytic facilities. Involvement in Green Drop programme is a priority for both eThekwini and Umgeni Water, and its continuous improvement component provides the motivation for committing special resources to it, such as employing models to practical use.

In this study, PRG and UCT are applying wastewater treatment plant models to a selection of WWTPs in the eThekwini/Umsunduzi region, and use these models to monitor plant performance over extended periods. The team aims to establish norms of expected WWTP performance, based on the data’s configuration and the characteristics of the incoming wastewater. Finally, the team is establishing methodologies for identifying critical barriers to improved performance, and developing a framework for integrating the above modelling/monitoring methodologies into the Green Drop programme.

At present, the site locations for wastewater treatment plants are being reviewed for selection. Two sets of WWTPs will be selected. The first set will include plants which receive high industrial loads, such as Umbilo, Verulam, Darvill and Hammarsdale. The selected plants will be under intensive investigation because of the special characterisation of the wastewater that they treat. Measurements required for the characterisation will be undertaken by EWS and Umgeni Water as far as possible, supplemented where necessary by the University's laboratories. The second set of WWTP will be modelled with minimal effort, using assumed wastewater characteristics as far as possible, probably including characterisation results obtained from the first set. The only measurement specific to a particular WWTP will be the routine measurements.

Once the WWTPs have been identified, an initial exploratory modelling phase will commence in which both the steady-state (spreadsheet-based) and dynamic (WEST based) versions of the UCT plant-wide model, developed under WRC project K5/1822, will be employed.

As the research progresses, the developed WWTP models will be used to regularly monitor the performance of the selected WWTPs. The correspondence (or lack thereof) between model predictions and plant measurements will be analysed to identify and address shortcomings in the models or measurement procedures, and to evaluate the adequacy and practicality of using the steady state and dynamic versions of the model in this context. In addition, the agreement between model predictions and operating data will be analysed to assess in what circumstances and to what extent modelling can provide a benchmark for plant operation and identify operational deficiencies. Using the results of this investigation, the research team will engage with the EWS and Umgeni Green Drop auditing teams to incorporate model- based plant modelling into their protocols. These will be tested during the 2015 Green Drop campaign.

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