College of Science, Engineering & Technology

Research that converts waste into energy and fertiliser while preserving the climate

Share

Prof Tonderayi Matambo

Prof Tonderayi Matambo from the Institute for Catalysis and Energy Solutions (ICES), formerly known as the Institute for the Development of Energy for African Sustainability (IDEAS) at the College of Science, Engineering and Technology, recently delivered his inaugural lecture titled "Anaerobic digestion: from waste management to energy and agriculture". 

Setting the scene, Prof Thenjiwe Meyiwa, Unisa Vice-Principal of Research, Postgraduate Studies, Innovation and Commercialisation, said: "Prof Matambo's lecture demonstrates our commitment as Unisa to look at the suffering that our environment has to withstand (and by extension, human beings), and conduct relevant research to address the challenges."  

The amount of waste produced globally has increased significantly over the years. In 2022 alone, 2 billion tons of municipal waste were produced globally. Projections indicate that this amount is expected to triple in sub-Saharan African countries and double in Asian countries by the year 2050. "In South Africa, 122 million tons of municipal organic waste is produced annually; only 10% of that waste is recycled, while the other 90% goes to landfills and illegal dumping sites," said Matambo. "The issue with this occurrence is that if left untreated, the waste seeps into underground water and contaminates it. In the process, greenhouse gases are produced, contributing to global warming," he stressed.

On the other hand, waste produced from leftover food and animal manure goes through a process where they have carbon dioxide and methane gases, collectively referred to as biogas. Methane gas is a more potent contributor to global warming. New methods of converting methane into less harmful products motivated Matambo's research interests to look deeper into biogas. Using anaerobic digestors ("anaerobic" means "in the absence of oxygen", and "digestor" is "a closed tank"), his research group feeds agricultural waste stock into the digestor. It captures methane and carbon dioxide gas that is produced.

"Inside the anaerobic digestor are microorganisms which are either bacteria or antibacterial, that convert the waste into biogas which can be processed further to produce fuel and electricity. What remains in the digestor after the anaerobic digestion has taken place, the 'digestate' which is rich in nutrients (nitrates and phosphates) is then converted into fertiliser, or used for livestock bedding and soil amendments," added Matambo. In his research, the digestate is used in spinach as a biofertiliser to determine its effects on plant growth and as a replacement for chemical fertilisers. His research further examines how biogas fits in with the United Nations Sustainable Development Goals (SGDs), including zero hunger, affordable and clean energy, and climate action.

Towards the end of his lecture, Matambo highlighted the significant benefits of biogas compared to liquefied petroleum gas (LPG) used in our household gas cylinders. These are summarised in the table below:

LPG (C3 and C4)

Biogas
The cost of LPG cylinders increases year after year especially in winter. One-time investment only. Raw material required is free waste.
With rising demands, obtaining an LP cylinder can be tedious. Continuous supply of biogas from your own plant.
LPG is heavier than air. So even small leaks cause fire, explosions and even death. Biogas is lighter than air and therefore escapes into the atmosphere in the event of any leaks.
LPG is a by-product of crude oil, a now renewable source. Biogas is a readily available organic waste which is converted to useful energy and fertiliser (renewable energy).
Uses of LPG: heating, moto fuels, refrigeration, cooking. Uses of biogas: heating, moto fuels, refrigeration, cooking, power generation.

Peer praise

Responding to the lecture, Prof Riann Christiaan from Unisa's College of Agriculture and Environmental Sciences emphasised the relevance and significance of Matambo's lecture and research since global food production must increase by 70% by the year 2050 to meet the demand for food. "According to the CSIR, food waste has a triple negative effect, hurting the economy because water, electricity, seeds, fertiliser and other inputs used to produce food are wasted if food goes to waste," he said. "Therefore, Matambo's research on this pertinent issue is encouraging and inspirational," he added.


Research and academic citizenship prowess

Matambo completed his PhD degree in molecular biology at the University of Witwatersrand (Wits), South Africa. His postdoctoral fellowship at Wits introduced him to biofuels and biological wastewater treatment research, which ignited his spark to conduct research in biogas technology. With 15 years of bioenergy and wastewater treatment research experience, he has become a registered professional natural scientist and a C3 NRF-rated researcher. He has published several peer-reviewed journal articles and book chapters. He is an editor and co-author of the book: Natural Wetlands: A Holistic Overview towards its Biomimicry for Application in Industrial Effluent Bioremediation. To date, he has supervised master's and doctoral degree students in the fields of science, engineering and biotechnology to completion. Moreover, Matambo has designed and constructed pilot-scale wetlands for wastewater treatment and biodigesters for biogas production installed in communities across South Africa. He currently serves as a project leader of a newly formed centre of competency in environmental biotechnology, sponsored by the South African Department of Science and Innovation.

* By Dr Nozipho N Gumbi, Acting Communication and Marketing Specialist, College of Science, Engineering and Technology

Share

Publish date: 2023/04/18

Unisa Shop