Methane mining in Africa could unleash deadly gas cloud

As if Africa — and Rwanda in particular — did not have enough problems. Beneath the shimmering surface of Africa’s Lake Kivu, a deadly time bomb awaits. A “gold rush” to extract valuable methane from the lake’s depths might trigger an outburst of gas that could wash a deadly, suffocating blanket over the 2 million people who live around Kivu’s shores.

The lake, which is almost half a kilometer deep in places, is on Rwanda’s north-west border with the Democratic Republic of the Congo and contains a vast reservoir of dissolved methane. Many companies are extracting the gas to burn for electricity production, and the governments of both nations are aggressively courting further investment in extraction plants.

Shanta Barley writes that now a group of biochemists warns that if unregulated extraction continues unabated, it could trigger a catastrophic outgassing of carbon dioxide — another dissolved gas abundant in the lake’s depths. Such a disaster occurred at Lake Nyos in Cameroon in 1986, killing 1,700 people. Kivu contains 300 times more CO₂ than Nyos did, warns Alfred Wüest, a bio-geochemist based at the Swiss Federal Institute of Aquatic Science and Technology (Eawag).

Like Nyos, Lake Kivu is permanently stratified: a deep layer of dense water laden with CO₂, methane, salt, and nutrients is locked away beneath a surface layer of fresh water. Methane is generated by lake-bed bacteria that feed on a stream of dead algae sinking from the surface. The CO₂ enters through volcanic seeps.

So far, the Rwandan government has established one methane extraction plant on the lake, and two companies — Contour Global and Rwanda Investment Group — are running pilot projects. At least two more plants are in the pipeline, says Eva Paul of Rwanda’s Ministry of Infrastructure. These will support the country’s plan to expand electricity access from 6 per cent of the Rwandan population to 16 percent by 2012.

According to a report by 15 researchers at Eawag and other institutes, certain current practices could trigger a catastrophic outgassing when methane extraction becomes widespread, as it will in the near future.

Perhaps the most dangerous practice is pumping waste water into the lake’s shallows. “If degassed water is dumped at the surface, it sinks, mixing water and salts between the lake’s layers,” says George Kling, an expert on the Lake Nyos disaster at the University of Michigan, Ann Arbor, who was not involved in the report. Enough mixing would disrupt the density stratification of the lake, and could bring huge volumes of CO₂-rich water to the surface. The pressure reduction would cause the CO₂ to bubble out of solution. Instead, waste water must be re-injected where it came from, the report recommends, at a depth greater than 270 meters.

Unfortunately, there is an economic incentive for companies to pump waste water into the shallows, says Finn Hirslund of COWI, a Danish environmental and engineering consultancy. This nutrient-rich water triggers algal blooms that then die and sink, helping to form even more methane. “If companies mess around with the lake’s density structures and accidentally trigger an entirely avoidable and deadly gas outburst, it will be a crime against humanity,” he says.

Barley writes that the Rwandan government, which commissioned the report, received it in June, but none of the recommendations has been applied or enforced so far, claims Kling. “There are no regulations in place as far as I know,” he says. “Our hope is that we can get the governments to require and enforce regulations.”

Hirslund believes that the Rwandan government has been too eager to win investment. “They have failed to put in place sufficient regulations to prevent malpractice,” he says.

Rwandan officials insist that they are enforcing regulations. “All the recommendations within the report are sincerely followed,” says Paul. But she admits that while all new facilities will be obliged to follow the rules, the government’s own plant will not be bound.