Water Week: Effluent recycling - an energy-efficient solution

As the City of Cape Town faces a demand for water that could outstrip its supply in the near future, research by a UCT master's candidate suggests that a water-supply portfolio that maximises effluent recycling should be a preferred policy option in the quest to balance water demand and energy expenditure.

Fadiel Ahjum, a master's candidate in sustainable energy engineering, also noted that expanding Cape Town's surface water resources would result in relatively low energy consumption but lead to a more vulnerable water supply system, as a scenario of reduced dam inflows suggests.

Ahjum argued that sea water desalination would improve water security, via supply availability and reliability, at the expense of energy consumption.

Ahjum's dissertation, titled Energy for Urban Water Services: A City of Cape Town Case Study, used the Water Evaluation and Planning (WEAP) hydrological modelling tool to develop a model for urban water services for the city. This evaluated a representative portfolio of water-supply options that the city had previously identified for their impact on the municipality's future energy requirements, along with the efficacy of the portfolios in reconciling demand and supply.

"The city has identified effluent recycling and (sea water) desalination in its appraisal of future water supply options, but it's hard to know how, or if, the city will implement the available options," said Ahjum. "At present the City appears to be pursuing the more cost-effective alternative of a water conservation and water demand management programme. This has the potential to delay further water supply augmentation by five to 10 years, depending on population and economic growth rates for the city."

While Cape Town is fortunate that rainwater from the mountainous regions collects and supplies 97% of the current municipal supply, the city needs a Plan B to guarantee water security during periods of drought, said Ahjum.

Ahjum, whose dissertation is currently being reviewed by the custodian responsible for the resources assessment of the Western Cape Water Supply System, noted that public perception and the required capital (recycling water to potable standards is an expensive business) were also central to dictating which routes cities took to improve provision of essential services.

"Public acceptance is an important consideration, as was recently demonstrated by the reported public outcry to such a proposal by the eThekwini Municipality, with desalination being the public preference."