Dr. Chris Buckley at the wastewater treatment plant at Newlands Mashu

Our contemporary lifestyle and extensive use of organic chemicals in personal care and consumer products (PCCPs) leads to the constant discharge of enormous quantities of chemical residues from industries and homes into wastewater streams, and ultimately the environment. In contrast to heavy metals, pathways of trace organic chemicals (TOrCs), derived from manufacturing and use of PCCPs, in the wastewater stream are varied. The majority of TOrCs that reach the wastewater treatment plants (WWTPs) are destroyed through wastewater treatment and sludge processing, but recalcitrant TOrCs and their metabolites can pass through the treatment process intact, and partition - dependent on their physico-chemical properties, in biosolids and aqueous media. In-depth knowledge of the chemical constituents present in environmental media is essential for the assessment of the associated risks to the environment and human health (bioaccumulation, persistence). Very little is known about the fate of TOrCs in the climatic context of South Africa.

In this project a number of different classes of pollutants were investigated: flame retardants, the broadspectrum herbicide glyphosate (Roundup, ubiquitously used in the local sugarcane industry) and its breakdown product aminomethylphosphonic acid, antibiotics, pharmaceuticals and personal care products, illicit drugs and HIV-ARVs. Influents and effluents from five wastewater treatment plants in the Durban area, including two receiving rivers, biosolids, and biosolid-amended soils were analyzed and characterized regarding the presence of these TOrCs. Of particular advantage for this project was access to a local decentralized wastewater treatment system (DEWATS) plant, which are envisaged to be the plants for the future.

This project has shown that some of these compounds are persistent and build-up especially in the receiving rivers into which the effluents are discharged (due to the increase in concentration of the micropollutants). A high removal of these micropollutants was observed in WWTPs that utilised an activated sludge process as its major process of treatment as opposed to those plants that only used screening and sedimentation. However, the DEWATS treatment train, which has longer solids retention and hydraulic residence times than the centralized WWTPs and utilizes primarily anaerobic treatment processes, was able to remove compoundsbetter. This DEWATS systems show promise for peri-urban areas not served by conventional sewer lines and cities of the future in Africa.

Risk assessment studies carried out on selected antibiotics in the study area showed that the effluent discharged and the receiving rivers could potentially initiate antimicrobial resistance to clarithromycin, azithromycin, and trimethoprim. Also, a low to high toxicity risk of antibiotics in the influents and rivers was observed to algae, crustaceans, and fish.
Wastewater-based epidemiology (WBE) is a tool that provides a real-time profile of community health and lifestyle. It was applied for the first time in the province of KwaZulu-Natal to understand and monitor trends in pharmaceutical and illicit drug use patterns within the eThekwini Municipality. This is importantfor public health monitoring. Amphetamine and cocaine were the prevalent illicit drugs consumed, while caffeine was the most consumed among the pharmaceuticals studied. It is well documented that fat soluble (lipophilic) TOrCs show very high affinities for organic carbon, and favorably partition into biosolids during solids separation, and thus are intrinsically less bioavailable than hydrophilic TOrCs in the soil-water environment. In South Africa and some other countries, growing amounts of stabilized sewage sludge are being applied to land, and in some cases, sewage sludge is directly applied as an organic fertilizer. Consequently, this may be an important route of contaminant dispersal through the environment. Toxic compounds, for example, TOrCs, heavy metals and pathogens, could compromise the beneficial use of sewage sludge. It is critical to establish the safe application rate of sewage sludge under different environmental conditions, and understand if and how TOrCs accumulate to phytotoxic concentrations.

Presently, sludge producers and legislators in South Africa are uncertain whether to encourage the use of sewage sludge in agriculture due to a lack of knowledge of the potential risks. Currently in South Africa, sludge legislation and guidelines are focussed mainly on heavy metals and pathogens. They are largely based on data from other countries and mostly centred on theoretical risk assessments. There is a lack of knowledge on the presence, levels and behaviour of TOrCs in effluent, sewage sludge and biosolids applied to agricultural land under South African climatic conditions. Our work has shown that relatively high concentrations of flame-retardants (lipophilic compounds with adverse health and environmental effects) build up in the sludge. However, these concentrations are significantly reduced when the sludge is treated, that is, in what is termed biosolids. The same was observed for the broad-spectrum herbicide glyphosate and its main metabolite. Our study of plants cultivated on biosolid-amended soils showed that there is a low risk of the uptake of glyphosate or its metabolite.

There are a number of developmental impacts of this project. From a scientific point of view, comprehensive target and non-target analytical techniques were developed to detect and quantify different classes of compounds in the selected matrices. The methodology developed will be of use to others in the field.

The fate of selected TOrCs during common effluent and biosolids-treatment unit processes was investigated. This provided them with a much better understanding of the efficacy of local WWTPs. It allowed them to understand which compounds constitute a threat to the environment. The potential human health and environmental risks associated with TOrCs present in the sample matrices was determined, and a comprehensive list of the selected TOrCs based on their prevalence and associated risk to the ecosystem can now be compiled. This is particularly important information for water re-use strategies in a water scarce country such as South Africa.

This project has shown that DEWATs plants are potentially suitable for future expansion projects. Additionally, the project has had an impact in terms of human capital development through the production of doctoral theses and MSc dissertations, and exchange of ideas and researchers with the US partner, Dr Mladenov. The supplementary grant provided enabled the Dr Mladenov’s student to visit their laboratories and perform research together with the project’s students. This interaction was invaluable.

Finally, local water authorities, such as Umgeni Water, eThekwini Water and Sanitation, the Department of Water Affairs, and the Water Research Commission will be actively approached and informed of their findings, hence forming the foundation for policy development.

The project's  future research plans are centered on devising suitable materials that can be used for polishing wastewater effluent to make it suitable for re-use. The use of two main technologies, adsorption and chemical oxidation/reduction, for the removal or destruction of recalcitrant micropollutants from sewage effluent will be studied. In both these areas the application of nanotechnology has been recognized as playing an important role in resolving many of the problems associated with water purification and quality. Carbon-based nanomaterials for adsorption will be prepared by making composites of functional carbon nanotubes or graphene oxide, with magnetic materials (e.g. cobalt ferrite) and waste biomass that contains an abundance of functional groups for suitable binding to micropollutants. These composites can be prepared by in-situ methods where the components of the composites are mixed in the necessary proportions and reacted together to give the final product. The nanomaterials can also be decorated with nanoparticles to impart disinfection properties on these materials besides their adsorption properties. The photocatalytic materials will be tested for their ability to photodegrade residual organic pollutants with visible radiation in the effluent. Various perovskite materials, or materials containing graphitic carbon nitride or vanadates will be prepared. The materials will be tested at lab scale (both synthetic mixtures and real sewage effluents will be tested). The efficiencies of the sewage effluent polishing technologies will be assessed by microbiome analyses.

The PI was elected as a Fellow of the Royal Society of South Africa, which is a great honor. She was also chosen to co-chair the forthcoming 2nd Commonwealth Chemistry Congress to be held in Trinidad and Tobago in May 2023. She forms part of the Programme Committee for the Atlantic Basin Conference on Chemistry to be held from 13-16 December 2022 in Marrakech, Morocco.