Professor Evans Chirwa is best known for introducing South Africa to the use of biological analogues for advanced water treatment and water recovery, to the use of synthesised materials to mimic processes such as biological reduction and detoxification of metals, microbial fuel cells and heterogeneous photocatalysis for water treatment. 

Chirwa’s latest work uses photocatalytic nanomaterials to treat organic pollutants. The project originated as part of a proposed solution for water treatment plants to treat backwash water for recirculation. It was part of an initiative started by Chirwa as Rand Water Chair in Water Utilisation Engineering at the University of Pretoria. 

The materials and processes developed by Chirwa and his team make it easier to reclaim and resupply scarce water resources. Various products are already proving their commercial worth with their ability to degrade organic water pollutants. More are being developed and tested with the aim of saving water at treatment plants, among other uses. For example, data from Sedibeng Water in the Free State revealed that more than R30-million in potential revenue is lost to waste in sedimentation sludge dams during three algal bloom months every year. Algae is difficult to remove from water and produces organic metabolites with complex molecular structures, also hard to treat.  “Treatment and recovery of this water could capture this revenue and help to address water scarcity in South Africa,” says Chirwa. 

The range of potential applications of Chirwa’s work includes using sewage plants as energy generation units, converting waste to energy in mining effluent, and converting degradation processes in landfills to electrical energy. His pioneering work in the field of nanoparticle photosynthesis has found use in other cutting-edge research too, such as H2O-splitting hydrogen production for the clean-energy hydrogen economy. It is also proven to be effective in treating water containing agricultural herbicides and antibiotic pharmaceuticals. Applications in forward osmosis (FO) membrane technology are promising too, where clean water is drawn from saline water using electrolytic polymers as Draw Solutions (DS). This energy-saving separation process mimics the osmotic processes that occur naturally in plants. Demonstration units for application of proton selective membranes and co-deposition of palladium (Pd) nanoparticles are under evaluation for energy generation from wastewater using microbial fuel cells. 

“There is no doubt that the novel nanomaterial products developed in our studies will play a major role in shaping the direction of water use and water reuse in South Africa. Apart from this demonstrated potential, the project has already had a resounding impact in training for the water sector in South Africa and the sub-Saharan region of Africa,” Chirwa says. Midgley believes we have come a long way over the last 30 years and points to the work done by the UN through its Framework Convention on Climate Change, Convention on Biodiversity and Ecosystems and other multilateral agreements. “These have completely changed the story of the future development of the planet. Aspirations are massively changed and they are starting to roll out in reality,” he says. — Elaine Williams

Read the special Mail & Guardian supplement about all the NSTF-South32 Award winners.