Co-Composting Human Excreta with Garden Waste Investigated in Master’s Research

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Master’s research by Ms Sinikiwe Khumalo investigated co-composting human excreta with garden waste, diverting large amounts of waste from municipal landfill and wastewater treatment plants and using co-compost to enhance the growth of plants.

Khumalo achieved excellent results for her master’s degree which was based on the circular economy.

From Delfkom in Mpumalanga, she had attended under-resourced schools, with her high school known for its high matric failure rate, however Khumalo excelled, earning the Mayor’s Award for the best student in the district.

Having taken agriculture as a subject in high school and growing up around people who relied on subsistence agriculture, Khumalo developed a love for the subject, learning that it could be an avenue for academic development. Supported by her teachers, she applied to universities to fulfil her dream of earning a degree.

The first in her family to attend university, Khumalo turned down an offer of doing a BCom at another university to study agriculture at UKZN where proximity to home and high positioning national rankings made it attractive.

Her fourth-year project involved optimising the mixing ratios of green waste and sewage sludge for co-compost production, working with Duzi Turf in Pietermaritzburg where her research demonstrated the potential to reduce pathogens to undetectable levels, the resulting compost suitable for use in agricultural plant production. She won second place in the oral presentation category at UKZN’s Postgraduate Research and Innovation Symposium (PRIS) in 2023. 

While she didn’t plan on progressing to postgraduate studies, the success of the project and the encouragement of Professor Alfred Odindo inspired her to do her master’s degree on a similar theme.

Despite not receiving funding for her work, a UKZN postgraduate scholarship and funding through the Rural-Urban Nexus: Establishing a Nutrient Loop to Improve City Region Food System Resilience (RUNRES) project enabled Khumalo to work on co-composting garden waste and human excreta, diverting a total of 15.6 tons of waste from Msunduzi’s municipal landfill and wastewater treatment plant. She explored turning frequency and mixing ratios to determine the best results.

Mr Jonathan Ogwang on the RUNRES team used the co-compost produced during her study for his PhD study while a horticultural sciences student at UKZN examined its effect on the growth of cannabis.

Khumalo found that co-composting dewatered sewage sludge with organic green waste significantly improves compost quality and cucumber seedling growth, outperforming commercial compost and sandy soil. Additionally, while most surveyed students at UKZN acknowledged the safety potential of treated human waste, consumer acceptance varied, with greater willingness to purchase co-compost-fertilised food depending on product type and perceived safety.

Khumalo won the first prize at PRIS 2024 and the Impact Prize for the practicality of her work. She also presented her project at the International Water Association conference, the Water Institute of Southern Africa conference, and UKZN’s Ukulinga Howard Davis Memorial Symposium.

She submitted two papers from her final-year and master’s work for publication. She is working on three more with colleagues.

Khumalo plans to enrol for her PhD under Odindo’s supervision, boosting her family’s pride. She will expand on her laboratory-based master’s study by measuring landfill emissions and examining contaminants of emerging concern to see how composting could reduce emissions. She hopes to produce scalable research that will have a real-world impact across the country.

Working as a demonstrator since her fourth year, Khumalo’s interest in academia and passion for helping students have developed, and she has received positive feedback from students, which encouraged her to pursue a career in this field.

Inspired by her church leader, Mr Jotham Mtshali, Khumalo also teamed up with her brother, an honours student at the Durban University of Technology, to begin a vegetable farming enterprise on 3.4 hectares near their home. She hopes that skills and knowledge from her younger brother, a second-year student in Animal Science at UKZN, will be useful in diversifying and expanding the farm beyond their current bean production and diversifying the farming enterprise to help support her family.

Khumalo thanked Odindo, her former principal at KwaMziwentsha High School Mr Bongani Mrwetyana-Khumalo, her mother Mrs Tobi Khumalo, her four siblings, and her church leader, Father Overseer Jotham Mtshali for inspiring and supporting her.

Words: Christine Cuénod

Photograph: Sethu Dlamini