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SAICHE iCHEMe Water management Thkozani MajoziStemming from a water management conference held at Wits in 2016 and funding and support from the British Council, the NRF, the Water Research Commission and Sasol, Water management: social and technological perspectives is authored by professors from three universities: Thokozani Majozi from SA’s University of the Witwatersrand; and Motiu Kolade Amosa from Cairo Iqbal M Mujtaba from Bradford University in the UK; University in Egypt. The authors have transformed case studies from 19 countries and 53 contributors into a 30 chapter, 571 page reference manual on the current state of the world’s water.

“It was Boutros Boutros-Ghali who first said: ‘The next war in the Middle East will be fought over water, not politics’,” says Majozi in introducing the Social Perspectives topic of the book. He highlighted several ongoing conflicts around the world, many of them relating to rivers shared by more than one country. “The dispute on India’s Cauvery River between Tamil Nadu and Karnataka continues to affect hundreds of thousands of people and the disagreement has been going on for centuries,” Majozi said, before adding examples of other water disputes related to rivers: the Okavango; the Mekong; the Rhine, Syr Darya dividing Kazakhstan, Kyrgyzstan, and Uzbekistan; and the Incomati, which is shared amongst South Africa, Swaziland and Mozambique.

Desalination technology is second of the book’s themes. Majozi shows a slide comparing the relative costs of the different technologies taken from commissioned operational plants: Multi Stage Flash at 1.5 US$/m3 in Singapore and 2.74 at the Saif plant in Qatar; Multi-effect Distillation in California at 0.46 US$/m3; Thermal Vapour Compression multi-effect in Qatar at 2.48; and, by far the most common, Reverse Osmosis (RO), for which Majozi cites three plants built at costs of 0.53, 1.1 and 0.50 US$/m3, respectively.

While describing how RO technology works, he points out that the technology uses high pressure to force pure water permeate through the RO membranes, separating out brine concentrate (retentate) for disposal. “Generating RO pressures takes energy, though, so although currently cheapest, other technologies may be more beneficial in the long term,” he points out.

Water Treatment also features in the book. Of note is the search for an alternative for activated carbon, currently used in 90% of water treatment facilities as an adsorbent for ammonia and nitrate. Several contenders have been found, including Ivy and strawberry leaves, which tend to be waste materials so they can be sourced easily and cost effectively. Of particular interest to South Africa and Egypt is the potential use of Water Hyacinth, which grows problematically on Hartbeesport Dam and on the Nile River. “Dried and pulverised, Water Hyacinth can be used as a direct replacement for activated carbon to give good adsorption from a fast growing and problematic plant waste,” says Majozi.

The Water Networks chapters in the book discus water reduction case studies from Bradford. Given the task of reducing water usage at specific sites, Iqbal Mujtaba and his team applied a technique called Water Cascade Analysis to systematically identify and implement savings solutions. “Any chemical process or facility has a point where the mass transfers are optimised. By routinely hitting these points wherever freshwater is involved, water usage can be minimised. Of the cases analysed by Bradford, 80% of the findings were actually implemented,” Majozi reveals.

Closer to home, he ends with a discussion on the Water Energy Nexus and his work at Wits. “South Africa is constrained by both energy and water. We are the 29th driest country in the world, out of 194 countries. Yet we need energy to get water and water to get energy,” he says.

Food is the third aspect of the nexus. “People need to plant crops to get food and crops need watering, which means using pumps that require energy,” Majozi explains.

“Also, though, chemicals almost always come into play in some way or another. In the 19th Century, predictions were that world population would be limited to about 2.5-billion people, but by the 20th the population was at least twice that at over 5-billion people. Why was the prediction so wrong? In 1918 we discovered ammonia, which led to fertilisers that doubled crop yields. So, a chemical changed the food supply aspect of the Nexus,” he relates.

Describing current research interests in this area, he says that his team is looking at the relationship between water and energy use. “At a typical plant, fresh water for cleaning, heating, cooling and process reactions is consumed and effluent is created. “Treating the effluent and reusing it can bring down water use and associated costs, but additional energy is needed to do this, which increases the energy costs.

“We are trying to come up with systematic methods of identifying the point of minimum total cost between the rising energy costs and the falling water costs, that is, the sweet spot or the optimum operating point for water recycling. We are already using this idea to do case studies to optimise water use by identifying water streams and recycling opportunities – and we have had some significant successes. At an old power plant, for example, which was designed to use 1.8 ℓ/kWh of water, usage has climbed over the years to 3.0 ℓ/kWh. Through direct reuse and recycling, we were able to reduce usage back down to 2.1 ℓ/kWh, and we calculate that we can get it back to 1.9 with a more costly intervention.

Before the intervention, plant usage was sitting at 119 Mℓ/day, which is approximately ¼ of the daily use of the City of Cape Town. Reducing usage is, therefore, a valuable and necessary exercise.

“Whenever more electricity is needed, however, we need to accept the associated water cost, and vice versa,” Majozi says.

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