Engineers rise to Rwandan methane extraction challenge

A team of Swiss engineers are helping the Rwandan government to identify a safe method to extract billions of cubic metres of methane from a massive lake in East Africa

For a number of years, engineers from the Swiss Federal Institute of Aquatic Science and Technology (Eawag) have been taking a close interest in Lake Kivu in East Africa. Their concern is focused on the hazard posed by billions of cubic metres of gases dissolved in the deep waters.

In a project sponsored by the Swiss National Science Foundation, the engineers are trying to harness a two-fold benefit from this methane resource: ensuring secure power supplies in the region for decades and reducing the risk of a deadly gas eruption.

Lying between Rwanda and the Democratic Republic of the Congo, Lake Kivu is about one and a half times the size of Canton Zurich and almost 500 metres deep (see ‘Focus on Lake Kivu’, below). The landscape around the lake is reminiscent of the foothills of the Swiss Alps, although banana and cassava plants grow on the slopes, rather than beech and pine trees.

Despite the idyllic setting, however, there lurks a serious hazard in the depths of the lake: approximately 250 billion m3 of carbon dioxide and 55 billion m3 of methane are dissolved in the water.

In recent years, the Eawag researchers have shown that the gas concentrations are increasing, with a rise of up to 20 per cent since the 1970s in the case of methane. At present, the gas remains dissolved in the bottom layers as a result of the high water pressure at this depth and the extremely stable stratification of the lake, which means that exchanges between the bottom and surface waters are very limited.

However, if gas concentrations continue to increase or if a severe disruption occurred – following a volcanic eruption or a major earthquake, for example – the situation could change rapidly. Large quantities of gas bubbles could rise to the surface, triggering a chain reaction that could lead to a massive gas eruption. The release of a mixture of carbon dioxide and methane gases could have catastrophic consequences on the densely populated shores of Lake Kivu, where roughly two million people live. Hundreds of thousands could be asphyxiated. In 1986, a disaster of this kind occurred on Lake Nyos in Cameroon, with 1800 people dying after a gas eruption.
The carbon dioxide in the deep waters of Lake Kivu mainly derives from volcanic activity; the methane is produced by bacteria decomposing dead organic matter (algae) in the anoxic bottom waters. The value of Lake Kivu’s gas reserves is currently estimated by experts at around CHF 16 billion (US$14.3 billion).