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CSIR researchers outline primary water quality research projects

27th September 2019

By: Schalk Burger

Creamer Media Senior Deputy Editor

     

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Scientists from the Council for Scientific and Industrial Research (CSIR) this week provided insight into their primary research on water quality and water treatment.

Three researchers detailed their research projects, which included designing and piloting a process to recover water and generate biogas to power some of the systems in a wastewater treatment plant from wastewater treatment sludge.

Another project was aimed at characterising and determining the associated risks of nanopollutants in water in South Africa, while the third research project entailed investigations into the quality of surface and groundwater in peri-urban areas.

CSIR Water Centre senior scientist and microbiologist Wouter le Roux provided an overview of the three-year research project to determine the characteristics and risks for human use of surface and groundwater in peri-urban areas.

The study, in partnership with the City of Tshwane and the Stinkwater community, north of Pretoria and west of Hammanskraal, found that surface and groundwater sources in these areas had high levels of nitrate, an inorganic pollutant that is associated with methaemoglobinaemia, especially in infants and young children, as well as microbes, some of which are pathogenic.

The study did not investigate the quality of piped water because the community relies on water trucked in from the Tshwane water treatment plant and on surface and ground water.

The study found that hand-dug wells, which were a common way for the people to get water, were often contaminated with microbes and nitrates.

Additionally, pit latrines, which are the main way of dealing with human excrement in the area, also increased the risk of contamination of groundwater. Surface waters were all found to be contaminated by e.coli, which are excreted with faecal matter by warm-blooded animals, typically livestock.

The research team took 144 samples in the wet and dry seasons, because rainfall has an impact on the quality of surface and groundwater. Chemical analysis of the samples found that 87% of samples contained too much fluoride, at about 2.5 mg/ℓ, and also contained about 23.1 mg/ℓ of nitrate on average, which is more than twice the legal maximum according to the South African water quality standard, SANS 241, which set the limit at 11 mg/ℓ.

The fluoride concentrations are not a cause for concern, although the levels could lead to tooth staining and impact on bone health.

"While microbes can be treated by chlorination, or the common use of household bleaches, filtration and ultraviolet treatment, nitrate cannot be removed as easily. Nitrate can have many potential health effects. The compound forms naturally and is produced by some large plants, smoke and industrial gases.

"In high concentrations, it can be dangerous for infants and pregnant women. Most of the common treatments require electricity and significant investment in equipment, such as ion-exchange, distillation or reverse osmosis. Suitable treatments in this area must be low-cost, easy to operate and suitable for interventions at a household scale," said Le Roux.

A subsequent three-year research project is investigating ways to treat the surface and ground water in peri-urban areas. The focus currently is on nano-engineered plates to remove nitrate through an ion-exchange approach, and phytoremediation, which involves using suitable plants to absorb excess nitrate through their roots in a hydroponic system, and could possibly help to produce food.

Le Roux warned, however, that these were not viable solutions yet, as increasing production of the plants may require additional fertilisers to be added, which would obviate the solution to reduce nitrate concentrations in outflow water.

He added that there was an infrastructure project under way to pipe water to Stinkwater, but that the research could have applications in other peri-urban areas, albeit requiring the characterisation of the raw water in the area.

Some areas of South Africa have naturally high concentration of nitrate in surface and ground water.

Meanwhile, research and PhD student Khuthadzo Mudzenani was part of the research project to beneficiate wastewater treatment sludge to produce biogas and recover water through a two-step anaerobic digestion process. The samples were analysed and the researchers found that they had low levels of chemical oxygen, which is important for anaerobic digestion, and was thick enough with sufficient total solid content, but would not produce sufficient biogas.

However, with the addition of suitable organic substrates, the production of methane is doubled and such a system can produce sufficient electricity to power some of the wastewater treatment systems, including heating equipment and a gas scrubber.

Additionally, about 12 Mℓ of potable water can be recovered from a 55 Mℓ wastewater treatment plant through the process.

The microbes present in the sludge, and used in the anaerobic digester, require a good nutrient balance and can work in an anaerobic digestion system.

The researchers identified sugar cane molasses; fresh produce waste, from canteens, dairy farms and fresh produce markets; and waste from breweries as suitable substrates for the process.

The team and the CSIR would now move to pilot the system at its innovation site.

"Beneficiating municipal wastewater would provide more potable water for communities, reduce the need to handle and dispose of the sludge after it has been dried out and provide electricity for some wastewater treatment plant systems," she said.

Lastly, researcher and PhD student Florence Lehutso focused on determining nanopollutants, which are particles in the 1 - 100 nm scale, in water and their risks to people. The team found that more than 200 locally available products contained nanoparticles.

However, she warned that this was a primary research project and was not exhaustive.

Nanotoxicity research and testing was in its infancy and not very robust yet. The project is ongoing and is investigating the impact of these pollutants on biotic organisms from different trophic levels.

"Nanotechnology is here to stay, owing to the benefits. We need to find the balance between the benefits of application and potential risks. There are no regulations of nanotechnology and nanoparticles in South Africa. We must learn from and avoid mistakes similar to those in the past, such as asbestos. We need to find ways to develop smart, nano-enabled products.

"The study was funded by Parliament and we are collaborating with industrial partners. The approach of the scientists and its industrial partners is to adhere to the concept of safety by design. This requires an understanding of the risks and uses of nanotechnology taking into account safety and the environment.

"The data from our studies contribute to policy making in the country," she said.

Edited by Chanel de Bruyn
Creamer Media Senior Deputy Editor Online

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