20 Quest Vol. 19 No. 2 | 2023 QUESTONLINE.ORG.ZA
THEME | FROM WASTE TO WATTS
FROM WASTE TO WATTS:
Leveraging AGROWASTE to address South Africa’s power crisis
While South Africa’s electricity shortage is not new, the situation has worsened significantly in the past 10 years. Attempting to protect the power-grid, ESKOM – South Africa’s electricity
public utility – has had to implement loadshedding stages and schedules, disrupting productivity nationwide. One potential alternative energy source is to incorporate fruit waste
into South Africa’s energy mix.
As a result of not having consistent power supply for several hours, loadshedding has negatively affected every facet of South African life. There are major disruptions to daily life, public services such as education and health, business operations, and normal functioning of electrical appliances and factory equipment. There have also been concerns about increasing loss of employment, environmental degradation and criminal activity.
Given these challenges, the use of alternative energy sources is urgent and necessary. As highlighted in the Bio-Economy Strategy, the use of renewable energy has been in the government’s agenda for over two decades.
However, by 2016 coal remained the country’s biggest source of energy, making up 85.7% of South Africa’s energy mix (Figure 1).
Currently, South Africa could benefit from renewable energy sources such as agricultural waste.
The agro-waste option
Agriculture is one of South Africa’s most vibrant sectors, producing a variety of grains (except rice), vegetables, deciduous and subtropical fruits, sugar, and oil seeds.
Particularly, the fruit industry produces a large variety of fruits, with apples, apricots, avocados, bananas, citrus fruit (grapefruit, lemons, limes, naartjies, and oranges), grapes, mangoes, peaches, pineapples, watermelons and melons produced in the greatest quantities. However, it was recently discovered that approximately 45% of the country’s total available food supply that enters the food value-chain, is wasted – especially during agricultural production and/or processing into various products.
QUESTONLINE.ORG.ZA Quest Vol. 19 No. 2 | 2023 21
FROM WASTE TO WATTS | THEME
Figure 1: Total electricity generated by source (DSSA, 2018) This poses a huge challenge to the environment, due to the emission of unpleasant odours, greenhouse gasses and toxic fluids that can contaminate water sources.
Consequently, health complications to communities that live nearby the dumpsite arise. But on the other hand, the food waste problem also presents an opportunity to use these fruit and vegetable trimmings, spoiled produce, and pulp to generate clean energy to mitigate the current energy crisis.
The energy from fruit waste is produced through biomass gasification – a process that uses heat, oxygen, steam, or a combination thereof, to convert food, agricultural waste and other biological materials into a mixture of gases that can be used as fuel (Figure 2).
Biomass describes any carbon-based material which when processed can produce liquid biofuels – biodiesel, bio-oil, bioethanol, biobutanol, and gaseous biofuels – hydrogen, hythane, and biogas (or methane).
Coal remains South Africa’s dominant source of energy
Total electricity generated by source, 2016
Biodiesel is produced by a process called
transesterification, where edible oils from fruit seeds can be chemically reacted with methanol and a catalyst to break down the oils into biodiesel. Biodiesel is environmentally friendly since it is carbon neutral (i.e. it does not produce carbon in the form of carbon dioxide).
Pyrolysis, a process involving heating biomass under anaerobic conditions, is used to produce bio-oil and syngas (a mixture of carbon monoxide, hydrogen, and methane). Similarly, under aerobic conditions, high- sugar food waste such as grape pomace undergo alcoholic fermentation to produce bioethanol. However, biobutanol is produced under anaerobic conditions by Clostridium species. Microorganisms such as bacteria and yeasts can be used to break down fruit waste matter under anaerobic condition to produce hydrogen or methane (Figure 2).
Hydrogen can be produced by light-dependent or light-independent processes known as photo-or-dark fermentations. However, hydrogen production is sensitive to temperature, partial hydrogen pressure, pH, volatile fatty acids, and food waste concentration.
When biogas is further processed through a
thermochemical step called gasification, hythane – a mixture of hydrogen (10 – 25% of hydrogen by volume) and methane – is obtained. This energy-rich and carbon- neutral alternative to the burning of fossil fuels may be an answer to the country’s electricity woes and environmental preservation.
Since South Africa has a thriving fruit industry, with a huge amount of fruit waste produced daily, it makes sense to utilise this agro-waste to supplement the country’s energy output.
Article written by Edwin Hlangwani, of the University of Johannesburg, and Dr Keleabetswe Lerato Mpye, of the University of Toronto, Canada.
Figure 2: The conversion of biomass into various biofuels
Academy of Science of South Africa (ASSAf)
ASSAf Research Repository http://research.assaf.org.za/
A. Academy of Science of South Africa (ASSAf) Publications D. Quest: Science for South Africa
