Biogas, food security and climate change


An interview with Bert van Nieuwenhuizen, chief technical advisor on shaping biogas markets in Africa.

This interview comes in two episodes; part one focused on the fine art of building viable biogas markets. This episode will explore the value of biogas fighting climate change and fostering food security_._


How is biogas linked to food security?

We started with biogas mainly from an energy perspective; clean cooking saves lives, money, and emissions. But bio-slurry – the process residue - turns out to be very valuable from an agricultural perspective.

This is especially important in Africa where soils are degrading very fast because of deforestation and intensive cultivation. This degradation is intensified by the effects of climate change on the weather; dry winds blow away nutrients and erratic rains erode the soil.

Sustenance of soil fertility depends largely on replenishing plant nutrients like nitrogen, phosphorus, and potassium. You need to put back what you take out. We call this closing the nutrient cycle. It is worthwhile to re-circulate local nutrients in the agricultural production cycle because it will lead to higher yields, without dependency on costly imported supplies. This is where bio-slurry or compost made from bio-slurry can prove its value.

What does that mean in practice?

Bio-slurry can be used as a potent organic fertilizer. Crops assimilate the nutrients in bio-slurry easier than those from raw manure. The slurry also improves the structure and water retention capacity of the soil. On average, agricultural productivity increases by 25%.

  • An average-sized household bio-digester will turn 15 tonnes of organic waste, manure, and 15 cubic metres of water into 30 tons of bio-slurry - which can fertilise at least 1 hectare of arable land.

  • Farmers can also use the bio-slurry to make compost, which may fertilise up to 3 hectares.

  • Excess bio-slurry and/or compost is increasingly being sold to fellow farmers.

  • The use of a digester will substitute on average 200kg of chemical fertilizer per year.

Woman in Kenya cooking by the light of a biogas lantern

Woman in Kenya cooking by the light of a biogas lantern

A young mason building a biogas digester in Burkina Faso

A young mason building a biogas digester in Burkina Faso

It sounds so good, why isn’t bio-slurry used more often?

Because biogas is usually looked at in isolation from livestock and crop farming. To get better results, we must step up integrating these subsystems. Are people able and willing to keep cattle? Do they have the right knowledge and skills about crops they grow?  Let me give you two examples.

About ten years ago our biogas programmes leapt to Africa, where we found a different situation from Asia, with most of the cattle roaming around freely. This makes it hard to collect their daily dung. So we worked with farmers to promote zero grazing - cows in the shed. This has implications for fodder production because these cows now need to be fed manually. We showed farmers how to use bio-slurry to fertilise fodder crops, providing a higher quality and quantity of feedstock for their dairy cows, which in turn resulted in a higher quality and quantity of milk production. Farmers especially noticed that well-fed cows maintained their levels of milk production during the dry season. What seemed the inevitable cycle of nature, could be controlled.

Brown Gold helps fight malnutrition

Climate change is already taking its toll. After decennia of progress, global hunger is on the rise, compounded by climate-related factors.  Burkina Faso faces recurrent spells of drought, causing food security challenges. The government wants to deal with these challenges, while at the same time reducing its dependency on imported chemical fertilisers.

That is why the government strongly supports our efforts towards commercialisation of the slurry value chain. An average bio-digester can produce up to 30 tonnes of slurry per year, which fertilises more than the usual one-acre farm. If well composted, the slurry can fertilise up to three hectares. Depending on the location, this may generate up to EUR 1,500 per annum. That’s why farmers call it the brown gold.

Because many farmers in this country cannot afford a biodigester, the government decided to subsidise them. Their reasoning is that bio-digesters are a public good.  No government asks its customers to co-finance building an electricity network, so why ask the full price for this decentralised public utility? The fact that biodigesters produce both clean energy and enhance food security, underlines its public importance as a climate-smart solution.

Green Biogas generates impressive emission reduction - Check this out: Biogas and aeroplanes

One average bio-digester of 6 cubic metres saves 4,000 kg CO2 each year through clean cooking (let alone the effect on fertiliser reduction). The figure probably doesn’t make a mark.

So, let’s compare this to the contemporary emission monster; an aeroplane. Using the graph below, using one bio-digester for one year saves the emission of five people flying from Amsterdam to Bejing, or 33 times from Amsterdam to Rome.

The direct impact of SNV’s 800.000 digesters installed (left aside the indirect effect of still prospering markets) has countered an emission equivalent of 30 million passengers flying from Amsterdam to Beijing.

A flight one way from Los Angeles to Beijing

A flight one way from Los Angeles to Beijing

How does a bio-digester reduce emissions?

First of all, it reduces the collection and burning of charcoal or firewood. A tree stores enormous quantities of energy (woven into its substance as it grew to its full length). All this energy is at once released into the atmosphere when you burn it.

Secondly, it transforms methane into CO2. Methane is found in cow dung and normally (especially in humid weather) ferments and evaporates into the atmosphere, but a bio-digester filled with dung confines it. The methane is piped to a cook stove where it is burned and thereby becomes CO2. We call this clean cooking for a reason, CO2 generates fewer emissions than methane.

And thirdly, bio-digesters produce fertiliser in a way that leads to less emission than chemical fertilisers. This effect is more difficult to quantify, therefore we keep it out of the equation.

Crops grown using biol or bio-slurry

Crops grown using biol or bio-slurry

A farmer spraying his crops with bio-slurry

A farmer spraying his crops with bio-slurry

To learn more about the topics or projects mentioned in this article, please contact Bert van Nieuwenhuizen at bvnieuwe@snv.org.