Peril and promise: Gas from ‘killer lake’ powers Rwanda

The engineers aboard the floating power station on Lake Kivu could only watch nervously as the volcano in the distance erupted violently, sending tremors rumbling through the water beneath them.

It was not the lava shooting from Mount Nyiragongo last May that spooked them, but the enormous concentrations of potentially explosive gases within Kivu, one of Africa’s great Rift lakes lying between Rwanda and the Democratic Republic of Congo.

Flanked by rolling green hills tumbling into glassy waters, Kivu is not quite the picture of tranquility it seems, according to Francois Darchambeau from KivuWatt, a company that extracts gas from the lake’s waters for electricity. Thousands of years of volcanic activity has caused a massive accumulation of methane and carbon dioxide to dissolve in the depths of Kivu -- enough to prove monumentally destructive in the rare event they were released.

If triggered, a so-called limnic eruption would cause “a huge explosion of gas from deep waters to the surface” resulting in large waves and a poisonous gas cloud that would put the lives of millions at risk, said Darchambeau, environmental manager at KivuWatt.

“This is what we call a killer lake,” the limnologist, or an expert in freshwater systems, told AFP.

Only three such lakes exist in the world: Kivu, and Lakes Nyos and Monoun in northwest Cameroon.

The latter two experienced limnic eruptions in the 1980s, and the bigger disaster at Nyos suffocated more than 1,700 people in a toxic release of carbon dioxide. But these catastrophes occurred in a rural area, whereas some two million people would be “at risk” of such a similar disaster involving Kivu, said Darchambeau.

In both Rwanda and DR Congo, many live in fear of the lake’s harmful potential, and stories abound of swimmers disappearing into its depths after being asphyxiated or pulled under.

World first

The lake, however, poses both peril and promise. 

KivuWatt, which says this is the only project of its kind anywhere in the world, saw an opportunity to tap these abundant gases for energy generation.

A 20-minute speedboat ride is required to reach KivuWatt’s unique floating platform, a compact tangle of pipes and buoys as high as a multi-storey building moored in the Rwandan part of Kivu.

With a deafening roar, the facility pumps water saturated with carbon dioxide and methane from around 350 metres (1,150 feet) to the surface.

As it rises, the water and gas separate as the pressure changes.

“It is like opening a bottle of soda,” said KivuWatt director Priysham Nundah, who described the project as “halfway between a thermal and a renewable energy plant”. 

The extracted methane is sent through a pipeline to a second facility located onshore in Rwanda, where the gas is transformed into electricity.

The carbon dioxide is pumped back into the lake at a precise enough depth to ensure the delicate balance is not upset.