Last December, the South African National Energy Development Institute (SANEDI), in partnership with the University of South Africa (Unisa) and mining company Exxaro Resources, opened an institutional anaerobic biogas digester at the Earth Centre in Johannesburg. The 10 m3 bio-digester runs on a feedstock of diluted horse manure, and produces biogas fuel for heating applications. The hope is that the biogas will eventually serve as a reliable and sustainable substitute for LPG or electricity in local homes, schools and community facilities.
Still … horse manure? For sceptics of renewable-energy technologies, the jokes seem to write themselves. Yet, for the likes of David Mahuma, GM of Working for Energy at SANEDI, it’s a very serious business, with very serious implications. ‘Biogas is a proven renewable energy that changes the lives of poor communities living in rural areas,’ he said at the launch of the bio-digester. ‘The installation of anaerobic digesters will be of great importance, not only in promoting the standard of living for people, but in helping the environment by minimising the amount of organic waste. Biogas usage is not limited to low-income communities, but also finds application in commercial and industrial applications.’
It’s also no laughing matter that about 65% of South Africa’s municipal organic waste – and nearly 100% of the commercially exploitable biomass generated from the country’s agricultural and food processing sectors – is still sent to landfill. This results in significant potential for greenhouse gas emissions. (In 2010, the waste sector was the second-largest contributor to South Africa’s total methane emissions, behind livestock.) It also means that all of that potentially valuable and useful organic waste is going, well, to waste.
With the government signalling a shift away from coal-powered energy towards renewables, sources such as solar, wind and hydropower tend to get all of the attention. But – as SANEDI’s new bio-digester suggests – biomass also has a significant role to play in South Africa’s sustainable energy future.
‘With the successful installation of the first institutional digester in the Gauteng province, 19 more are in the pipeline to be installed at a variety of locations in Gauteng, North West, Free State, Limpopo and Mpumalanga provinces, with a particular focus on institutions such as old-age homes, early childhood development centres, schools and clinics,’ said Mahuma. ‘The impact within institutions is greater than within households since more people stand to benefit from the system than in a family setting. The partners will look at smaller systems that are cost-effective that can be used by households.’ Mahuma added that SANEDI had already undertaken similar work using different feedstocks, including food waste, human waste, pig manure and cow dung.
SANEDI’s anaerobic biogas digester is not a first in Africa. The Gorge Farm energy park, located 75 km north-west of Nairobi, has been producing biogas through anaerobic digestion since 2016, generating 2 MW of electricity. To produce the same amount of energy using diesel would require about 5 million litres of fuel a year. Gorge Farm’s electricity production more than covers the power needed to cultivate its 706 ha of vegetables; and as a result it sends surplus power to the national grid, where it’s used to power up to 6 000 rural homes.
Tirivaviri Augustine Mamvura, a senior lecturer at Unisa, recently showed research confirming biomass’s potential for South Africa’s electricity mix. ‘There are some issues to consider, such as where the biomass will come from and the construction of special furnaces to perform the [torrefaction] procedure,’ he writes on the Conversation. ‘However, it is clear from our research that biomass could do the same duty as coal, with far less water use and less pollution. It is also a renewable resource, unlike coal.’
Mamvura identifies a handful of challenges that would have to be overcome before biomass could be considered a viable energy source. ‘The first is that some biomass, such as fruit and vegetables, is used as food. It will be important to identify biomass sources that aren’t used as food so that the technology doesn’t end up creating food shortages,’ he writes. ‘The best alternative at the moment is to use organic waste biomass from landfill sites or waste from forest processing. This would help to clean up the environment as well as tackle land and air pollution. After some time on the ground, the organic waste at landfill sites starts to decompose and release methane, which can lead to fires and air pollution. Using part of the waste would help reduce this. This is the approach other countries are taking at their biomass plants.’
It’s also the approach that’s being taken at a new bio-refinery facility in Durban. The ZAR37.5 million Bio-refinery Industry Development Facility (BIDF) was officially opened at the Council for Scientific and Industrial Research’s (CSIR) Durban campus by Minister of Science and Technology Mmamoloko Kubayi-Ngubane in March 2018. The BIDF aims to extract maximum value from biomass waste – including, but certainly not limited to, producing biomass-derived energy.
Its initial focus is the forestry (pulp and paper) sector, where bio-refining is currently practised on a very limited scale. Most of South Africa’s wood, pulp and paper waste goes to landfill, or it is burned, stockpiled or – in some instances – pumped out to sea. ‘I would like to really look at biomass as some form of gold, where in the past you may have been throwing away what you couldn’t use without knowing that actually there is value that can be extracted further out of this product,’ Mmboneni Muofhe, deputy director-general of technology innovation at the Department of Science and Technology, said at the launch of the facility.
Muofhe added that biomass research and development should not be limited to government agencies or big businesses. ‘When we look at how the bio-economy strategy is going to be implemented in terms of bio-refineries, the platform we are establishing looks at two concepts: one is where you get centralised facilities like this facility [in Durban]; but another is to look at how can you have decentralised facilities,’ he said. ‘That’s where you begin to reach out to those smaller players. You want to establish facilities for them not to be driving long distances to transport their biomass, but to have it at their doorstep.’
For Bruce Sithole, director of the CSIR’s Forestry and Forest Products Research Centre, the strength of the BIDF lies in its local application. ‘Indeed, bio-refinery technologies have been used overseas, and people may wonder why we don’t take those technologies and apply them and use them here,’ he says. ‘But it’s not necessarily as simple as that. You need to take those technologies but you need to be able to adapt them to the local conditions. This is where our facility comes in.’
In the South African context, any conversation about energy has to include the country’s beleaguered coal-fired power stations. And while biomass may be a promising emerging energy source, it is nowhere near ready to replace coal just yet. As Unisa’s Mamvura writes, ‘it will […] take a lot of biomass to replace even a small fraction of the 90 million tons of coal that [state power utility] Eskom uses annually at its power stations. For instance, we calculated that to replace 10% of that coal, at least 14 million tons of raw wood waste would be needed’.
Still, replacing even a small part of South Africa’s coal-heavy energy production with biomass will have positive environmental benefits, and could help move the energy sector towards renewables. Whether that biomass comes from wood chips, sawdust, grass or even horse manure really shouldn’t make much difference. At this stage, the research focus is on finding – as Muofhe puts it – the ‘gold’ among the waste, and using that to heat up South Africa’s economy and light up its energy sector.
By Mark van Dijk
Images: Sappi, Alamy