Biogas — the gas in the energy mix South Africa could comfortably use

Of the multitude of crises facing South Africa at the moment, the energy crisis probably receives the most coverage; “load shedding” is a swear word among South Africans. Other problems, however, are more likely to be top of mind for those directly affected by them.

Millions of South Africans still lack access to basic safe sanitation and, to make matters worse, it is reported that roughly half of the country’s sewerage works fail to treat sewage properly while some 40% are in critical condition. On the opposite end of the digestive tract, South Africans also face soaring food prices, driven in part by record fertiliser prices as the Ukraine conflict affects global supply.

If only there were some way to turn sewage into energy and fertiliser, we could tackle all three crises in one fell swoop. Fortunately, there is. Anaerobic digestion is a process that uses microorganisms to break down biomass to produce biogas, a mixture of methane and CO2, as a source of energy. The solid matter and dissolved minerals that are left over, referred to as digestate, are a valuable fertiliser rich in phosphate, potassium and trace minerals, while the urea content of urine supplies nitrates.

Biodigestion is a well understood technology, and has been implemented all over the world at various scales. China is considered the world leader in biodigestion, producing some 15 billion m3 of biogas per year, equivalent to around 200GWh per day, which is around 40% of South Africa’s daily electricity use. The majority of this is produced in small-scale digesters, mainly household- or community-scale units.

It is estimated that there are almost 50 million biodigesters operating throughout China, and no wonder; China has employed various different subsidy schemes to encourage their adoption since the 1970s and everything needed to set up a biodigester can be easily bought through Alibaba, on a reasonable budget.

This widespread personal adoption illustrates the simplicity and robustness of the technology. A small biodigester does not require heavy or expensive equipment to build, nor advanced technical skills to operate. The micro-organisms that do the digestion can be supplied by simply adding some cow dung at startup. The low-tech, low-cost nature of biodigesters make them an excellent fit for under-resourced communities in South Africa.

They are also a good match for South Africa’s energy requirements. At present, we do not lack total capacity; what we lack is peak capacity to meet surges in demand in the morning and evening, when large amounts of power are used for cooking, water heating and household heating. These applications can all be met directly by using biogas, mitigating those surges in demand without the infrastructure requirements (and inefficiencies) of electricity generation and distribution. Biogas is produced from materials which currently break down into CO2 anyway, resulting in net zero emissions of CO2 emissions when biogas is used for energy.