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PhD examines use of human wastewater to grow horticultural crops

Dr Shirly Magwaza earned her PhD in Horticultural Science by evaluating the feasibility of using human excreta-derived materials as nutrient sources for hydroponic production of horticultural crops.

Using Nitrified Urine Concentrate (NUC), a human urine-based fertiliser and effluent from domestic wastewater as the nutrient source, Magwaza grew tomato plants in a hydroponic system at the Pollution Research Group (PRG) Newlands-Mashu Research Site in Durban. Her research was supervised by Dr Alfred Odindo and Dr Asanda Mditshwa.

Magwaza recognised challenges to food production including water scarcity, nutrient-depleted soils, pollution, and a growing, urbanising population. Added to this the threats to environmental and public health arising from the insufficient provision of sanitation and wastewater disposal facilities, she adopted an integrated approach that offers sustainable management of waste disposal in a manner that could protect the environment and benefit society by allowing nutrient re-use and recovery for food production.

She demonstrated that the use of NUC as a main source of nutrients was not sufficient to produce an economic yield of tomatoes, with the low supply of calcium being a major limiting factor as it contributed to blossom end rot in tomatoes. Magwaza found that using wastewater effluents as a sole nutrient supply is not sufficient for tomato plants grown in a hydroponic system, evident in the low concentration of essential nutrients such as nitrogen, phosphorus, potassium, calcium and zinc in the wastewater. However, the addition of a commercial hydroponic fertiliser mix, CHFM, to anaerobic baffled reactor effluent resulted in increased plant growth, economic yield, nutritional quality and post-harvest performance of hydroponically grown tomatoes.

Magwaza has published five papers in high impact journals, Science of the Total Environment, Agricultural Water Management, Acta Horticulturae, and Agronomy.

Magwaza suggested there should be more focus on developing accurate cultivation practices to enhance the efficiency of using human excreta derived materials as nutrient sources for hydroponically grown tomatoes.

Magwaza completed her diploma in plant production at the former Lowveld College of Agriculture, now the University of Mpumalanga, her BSc at North-West University in Mafikeng, followed by a Master's degree at UKZN. Having completed her PhD, she will continue with postdoctoral research at UKZN under Mditshwa's supervision.

The pursuit of a PhD came with its own challenges for Magwaza, a mother of two children aged six and nine, and she said she had to juggle the responsibilities of being a wife, mother and student. During the final two years of her PhD studies, she also lectured at the University of Zululand, putting increased demand on her time and focus and necessitating that she work on weekends, and occasionally take her children along on data collection trips.

Magwaza credited her supervisors, Odindo and Mditshwa, for their guidance, patience and encouragement, and her husband, Professor Lembe Magwaza, for his support and encouragement in enabling her to pursue her PhD studies.

She thanked the PRG for their technical support and experimental space, and made special mention of students in UKZN's Agricultural Plant Sciences who supported and assisted her, namely Sabelo Shezi, Sizwe Mthembu, Sisanda Mthembu and Sisekelo Sihlongonyane. She also thanked her friend and colleague, Slindile Mkhabela, for her moral support.

Author: Christine Cu'enod