Power From The Depths

"Engineer Live" has an interesting article on avoiding a Lake Nyos style tragedy in the regions bordering Lake Kivu, between Rwanda and the Congo, and generating a large amount of power while doing so - by extracting methane from the lake water and using it for power generation.

The waters of Lake Kivu have absorbed enormous amounts of gas over the years, estimated to be around 250 billion m3 of carbon dioxide and 55 billion m3 of methane, with the total amount rising 20% since the 1970's. The lake sits at an altitude of almost 1500 metres above sea level and covers an area of about 2400 km2, with a maximum depth of 600 metres. Only two other lakes are known to harbour similar quantities of gases – Lakes Monoun and Nyos in Cameroon. In both of these cases, however, carbon dioxide predominates - the quantities of methane are too small for exploitation to be worthwhile.

The carbon dioxide in the deep waters of the lake mainly derive from volcanic activity, while the methane is produced by bacteria decomposing dead organic matter in the anoxic bottom waters. According to Swiss researcher Martin Schmid from Eawag, the rise in methane concentrations observed over the past 20–30 years is likely attributable to two factors: a huge increase in nutrient inputs, associated with the growing population around the lake, and the introduction of a sardine species that has had a major impact on nutrient cycles.

The gas poses a threat to both the 2 million local inhabitants (in the event of a gas eruption from the lake) and the planet as a whole (methane being a potent greenhouse gas). Analysis of the lake's geological history indicates a periodic biological extinction around the lake around every 1,000 years. The trigger for lake overturns is unknown but scientists hypothesize that sufficient volcanic interaction with the lake's bottom water that has high gas concentrations would heat the water, force the methane out of it, spark a methane explosion, and trigger a nearly simultaneous release of carbon dioxide. The carbon dioxide would then suffocate large numbers of people in the lake basin as the gases roll off the lake surface. It is also possible that the lake could spawn lake tsunamis as gas explodes out of it.

The dissolved methane also provides an opportunity, as the gas can be extracted from the lake and used for power generation and other applications. The value of Lake Kivu’s gas reserves is estimated by experts at around CHF 16 billion (US$14.3 billion).

Extraction of gas has already been done on a small scale, with the extracted gas being used to run boilers at a brewery up until 2004.

The Rwandan government is in negotiations with a number of parties to produce methane from the lake on a larger scale. It recently awarded the South African engineering company Murray & Roberts a contract to construct a power station, with a pilot project to be initiated early this year. Efforts to establish a power station seem to have been underway for a few years now, with various delays being experienced. The BBC has also reported on a company called EcoEnergy looking to build a plant.

Extraction is said to be cost effective and simple because once the gas rich water is pumped up from the depths the dissolved gases bubble out as the pressure falls. The methane in the lake is estimated to be sufficient to meet Rwanda's needs for 200 years and 400 years. Using the gas may mean far less logging in the area since Rwanda currently gets 90 per cent of its energy from wood burning, with forests disappearing at a rate of 4% per year.

Like many other examples of renewable energy sources, this, by itself, is not a solution to the energy problem posed by peak oil - however, it is one more example of the dozens of local alternatives that can be exploited to meet our energy needs - and in an area cursed with trouble that, as Thomas Homer-Dixon pointed out, at least partially stems from competition over resources. This could be considered the aquatic equivalent of generating energy using biogas from landfills or farm waste.

Sounds pretty much like a win-win. We could turn it into a win-win-win if we use carbon offset funds from the richer countries to sequester the CO2. Counting this CO2 as sequestered (if we dispose of it properly) should be allowed. The CO2 in the lake will reach the atmosphere whenever the feared eruption event occurs. Additionaly the experience of trying to geologically sequester CO2 on this scale would provide important scientific data on sequestration.

If the CO2 and CH4 bubble up in the same proportion as they are present ie 5:1, cost of sequestration may be prohibitive. Much of the CH4 might be used up collecting, compressing and transporting the CO2.

This assumes sequestration can be made to work and that there is a suitable CO2 repository within economic distance. Around two million tonnes of CO2 would be produced each year. Anyone offering their back yard?

With 5:1 ratio this should be the most polluting NG power station in the world, GHG-wise.

Rough calculation - typically NG power stations release 600g CO2/kWh, plus 5 times that (from the associated CO2 released) brings the total to 3,600 g/kWH. This is 4 times more if they burnt coal!

Given that, calling this energy sources "renewable" is a bit ironical, isn't it? And, no it is not serious to expect carbon capture for this project - they don't do that in the West, how could anyone expect Rwanda to do it?! It's ridiculous.

Unfortunately the point is that every now and then the lake spews out a lot of the gas anyway.

So while this isn't "renewable", the CO2 in the lake waters isn't sequestered the way carbon is in coal either.

Burning the methane (or convertin it into fertiliser) and sequestering the CO2 somewhere (or as EP suggests, using it) is the best case scenario, but no the only one...

With 5:1 ratio this should be the most polluting NG power station in the world

And that CO2 would wind up where, in the natural scheme of things?

It occurs to me that this CO2 is produced nearly pure, and would be a perfect feedstock for e.g. algal ethanol/biodiesel systems.  The source will be emitting for thousands of years — it's as renewable as anything else on the timescale of human history.  If it is turned into fuel and burned, it would emit no more CO2 than the natural emissions of the volcanic processes.

Sure, taking that CO2 and injecting it into deep wells would be best for GW abatement.  Sometimes the best is the enemy of the good.

Something like the CO2 Wash process could be used to upgrade this gas to pipeline quality.

It is somewhat ironic that the methane in the lake comes at least partially from farm runoff.  Eliminating this input would cause the methane to be renewed more slowly or not at all.  To make this resource totally sustainable would require that the watershed keep putting excess nutrients into the lake — nutrients which could be at least partly produced from the methane itself (reform to hydrogen, convert to ammonia via the Haber process).

I have to admit, I find this little twist amusing.

Sounds like Cradle to Cradle agriculture :-)

This is the original BBC report from 1986:

The eventual number of people who died in the Lake Nyos gas leak was put at more than 1,700.

Scientists debated the cause of the disaster for some time afterwards.

It was finally concluded that the lake's lower levels had become saturated by carbon dioxide gas (CO2) due to gaseous springs which bubbled up from the extinct volcano beneath.

It is thought that recent high rainfall had displaced the CO2-rich water at the bottom, releasing a massive bubble of carbon dioxide gas from the lake in a natural phenomenon now referred to as "lake overturn".

The heavy gas then sank to the ground and rolled in a cloud several tens of metres deep across the surrounding countryside.

Pipes have now been put in place in Lake Nyos and nearby Lake Monoun to siphon water from the lower layers up to the surface and allow the CO2 at the bottom of the lake to slowly bubble out, preventing a repeat of 1986 tragedy.

Following the Nyos tragedy, a survey was carried out into the CO2 content of other African lakes.

It revealed that Lake Kivu, in Rwanda, is becoming saturated with carbon dioxide just as Lake Nyos was, and is seriously at risk of lake overturn.

Scientists have warned that if nothing is done, millions of people living around Lake Kivu are in danger.


This shows how dangerous CO2 storage can become. If this storage were ever done onshore, permanent monitoring ad infinitum would have to be done similar to nuclear dumps. I cannot imagine any EIS would be accepted by a local population once the dangers are known.
NASA climatologist Hansen therefore proposes storage in deep ocean sediments. This means that only coal fired power plants near the coast could have CCS if those suitable sediments were found.

Many earlier CO2 sequestration ideas are being doubted or at least having their potential reevaluated. It's not looking the best. We need to stop digging this hole.

One possible idea is here, brought up also recently in the drumbeat.


Here preliminary research shows the possibility of underground CO2 conversion to calcium carbonate. It's has a number of people nervous, for the area is just recovering from one government "oops". That oops created the Hanford nuclear "downwinders" of eastern Washington and Idaho.

For additional Lakes Nyos and Kivu information, see:


Here preliminary research shows the possibility of underground CO2 conversion to calcium carbonate. It's has a number of people nervous, for the area is just recovering from one government "oops". That oops created the Hanford nuclear "downwinders" of eastern Washington and Idaho.

I think you're conflating the Hanford project with WPPS (fancifully referred to as WOOPS, since it turned out to be such a massive boondoggle); it was Hanford that released radiation sprinkling it on the downwinders - of which I'm one, about the last batch to get a dose. People where I grew up in Eastern Oregon used to just suddenly up and die for no reason.

I've read about sequestering CO2 in the Columbia River Basalt - fascinating idea. The volcano or volcanoes that created the basalts were utterly awesome in their power - repeatedly flooded everything east of the Cascades, pretty much, about 15 million years back.

No, not confusing. The whoops was whoops, WPPS later changed to Avista, since then becoming a rather decent utility. The oops was the government converup/denial of radiation leakage from Hanford.

One of the dislikes of the sequestration is that once again their "good for nothing" desert has found a use, where they will have many new coal fired power plants to deal with. The coal is imported, the power and dollars are exported, and they are left with the mess, again. Here's hoping the mess really does calcify.

All you have done is to show the danger of CO2 leakage into lakes without annual (temperate zone) turnover.  If the lake turns over every year as the surface goes to freezing and again as it thaws, the buildup will be abated.  Leakage up into land (no storage), flowing water (no buildup), or overturning lakes (no storage) won't have that risk.

I recall reading studies which found that deeply-injected CO2 will tend to form carbonates, which cannot leak.  How much of the CO2 will be chemically bound is open to question, but it appears to be a fact that at least some of it will be.

Hi Big Gav,

question: does a thermal difference exist between the lake surface and the 600m depth? If so then since you are pumping water up anyway and if it is large enough you might be able to run a unit like an OTEC (Ocean Thermal Energy Convertor) from it. In addition cool lake water could be used for air conditioning in the hot summer months.

A few links;


Regards, Nick.

Hi Nick,

Presumably the depths of the lake are cold and there is a significant temperature difference - but I didn't see this discussed anywhere.

I did a little reading about OTEC a few years ago - there were some experiments in Hawaii and perhaps Japan being done - opinions were varied - as always :-) - as to whther or not this could produce useful amounts of power.

I see some places using cold water from lakes directly for cooling buildings (in Toronto, for example), but this probably isn't a great concern at Rwanda right now.

Thanks for the links - I'll check them out - I'll be doing a post on the potential for ocean power at some point and this was one area I was going to look into...

In a tropical climate there is unlikely to be any cold weather to create cold bottom water. So unless a cold mountain stream brings in water from a much higher elevation you wouldn't expect much thermal stratification. OTEC was much discussed thirty years ago, but it seems to have been largely abandoned. I did see one mention of someone looking at it recently, so the idea is not completely dead.

Believe it or not the mountains to the north of the lake have snow on them :-)

Well - they do for the moment - the glaciers are shrinking very rapidly - one more victim of global warming it seems...


I don't think a high temperature at depth is needed to run an engine off this resource (or a low temperature at depth, either). In its current form, it is blowing a stream of water 50m above the surface of the lake. That is already mechanical power. To capture that power requires water turbines as are used in a small scale hydropower facility and some ingenuity with plumbing to separate the mixed flow of gas and liquid. It does not require the high efficiency heat exchangers that are needed for OTEC. This would be a nifty local power resource. But keep in mind, this is one energy resource that definitely should be depleted, and not developed in a sustainable way.

I've heard proposals to run engines off a salinity gradient between fresh water and salt water. This would be an engine that runs off the gradient in CO2 concentration. OTEC is a heat engine. Heat engines run off a gradient in temperature. With the development of coal resource in Europe, a lot of effort went into the study of thermodynamics. A big branch of physics was created and, as a side effect, all sorts of other engines were invented theoretically. The resource needed to run any of them never had the availability of coal-derived high temperature, so they were never really turned into practical inventions.

OK, great. I'm one of the contributing editors to the otecnews site so if you need any input let me know. The Xenesys site has some useful stuff. This company has a process that greatly increases the efficiency of energy extraction.

I got quite excited over the potential of OTEC a few years back as it is a 24/7/365 deliverer of energy unlike the other renewables -coupled with perhaps the creation of Ammonia as a carrier and bulk transport from the tropics... Well, not done any costings and its currently a 'fantasy-tech' so won't help much for the next couple of decades...

...and 'enemy of state', you don't need cold water coming in, any water below a certain depth is in the dark and a lot colder than the sunlit surface water hence the thermal difference. Works like a ground source heat pump.


noutram, eos,

try this link for the thermocline and stratification profile of the lakes.


Temperature variation is small, but traces a step "C" to actually increase at the bottom. Here, stratification maintained by high density gradients. Fascinating.

Thanks - I might ask you some questions in a few weeks time...

I'm glad we haven't forgotten Lake Nyos. This fascinating discussion about harvesting the methane in Lake Kivu begs the question, what about the immense oceanic deposits of methane hydrate?
From Wiki, under "methane clathrate:"

Oceanic deposits seem to be widespread in the continental shelf and can occur within the sediments at depth or close to the sediment-water interface. They may cap even larger deposits of gaseous methane.

Locked up down there is the potential for an immense energy source, and the potential for an immense impulse of greenhouse gas release. An oceanic event like the landslide that caused Nyos to overturn could trigger the same kind of runaway event, but on a much larger scale. A candidate trigger might be a slump of the Big Crack on the big island of Hawaii:

A couple decades ago no one imagined that all that heat-trapping methane could be lying around on the seafloor, and now we're here thinking up ways to release it for our own use. Well, it may have its own schedule for release, and it may not work out to our best interest.

The question I want pose is, does increased heating of the atmosphere and the sea surface increase or decrease the stability of the thermoclines that help keep that methane locked up? And does it make any difference, in the light of the inevitability of earthquakes and landslides that will eventually disrupt the equilibrium?

Chapter 14 in Fred Pearce's With Speed and Violence: Why Scientists Fear Tipping Points in Climate Change is titled "The Doomsday Device: A lethal secret stirs in the permafrost". In that chapter, Pearce relays the report of a Russian scientist who has been visiting what had previously been permanently frozen parts of Siberia. He reports that in a recent visit he observed hundreds of miles of tundra now covered by small ponds and lakes - created from the meltwater of the now thawing ice - in which peat and other organic matter is now decomposing ANAEROBICALLY (because it is under water), producing methane. He reports that the ambient levels of methane in the local atmosphere are up significantly.

-- Philip B. / Washington, DC

Yes, there are data coming in from the Arctic and Siberia, because they're easier to observe than the sea floor. But what's happening on the continental shelves? As bad as the runaway-greenhouse possibilities are resulting from thawing of the permafrost, they pale in comparison to the impact of a sudden, near-total release of seabed methane clathrate, as in:

The methane ices are stable because of a combination of pressure and temperature. Warming of the oceans is not a good sign. Rising sea levels means the pressure at a given point on the sea floor is rising. I think the former factor is much more important. I think most of the methane is tens of meters under sediment, so the time scale for heat diffusion should be pretty long.

At least during the iceage to Holocence transition there is no evidence of a catastrophic methane release, so the overall system is probably not so sensitive to a few degrees of warming as some would leave one to think. Mechanical disturbances are a different matter, but thet would likely to localized and not global.

Remember Nyos: Once the edge of the lake was perturbed by the landslide, the effervescence started and it continued to stir itself, bringing more gas-saturated water close to the surface, perpetuating the cycle until the whole lake had turned over. What's to stop this same process from occurring on an oceanic scale?
IIRC, the residence time of methane in the atmosphere is less than ten years, so it's likely or at least plausible that the Greenland ice-core data cannot accurately reflect the methane contribution to past climate excursions. So "no evidence" may not mean much, given that the ice cores do indeed show many large, discontinuous temperature changes over timescales that are too short to distinguish.

The methane is not supersaturated in the sea water, but dispersed in the sediments in the form of hydrates. It requires energy to convert from hydrate to gas, so I don't think it would be so quick. The slow change of CO2 in seawater in response to temperature changes is sufficient to explain the glacial/interglacial CO2 concentration changes (180ppm ice age 280ppm interglacial). It would appear unlikely that methane hydrate releases had a significant impact on that transition. Of course lack of it happening during the last major climate change (which is not identical to the current one) is not proof that it won't happen. Rather it is proof that every warming climate change doesn't induce a methane hydrate event.

Methane hydrates are interesting, but I suspect from a global warming point of view there is more of a risk there than an opportunity.

Der Spiegel had a look at Chinese and Indian exploration in this area a couple of weeks back :


Exploiting these deposits (if that can be done economically) is a real mixed bag. Methane is such a good fuel it would be tough to stop. If methane isn't released to the atmosphere, but is burned then the CO2 emmisions/BTU is a lot lower than coal. And if the hydrates really are a geologic time bomb, we are defusing it. The problem comes that the scale of this resource is so large that if any serious fraction is burned the CO2 spike would be huge. I haven't heard of any attempts to cature CO2 from methane combustion, you get four water molecules for every CO2, plus the nitrogen from the air so that might not be an easy option. We already have three countries, India, China, and Japan investigating the possibilities.

Why hasn't anybody tried to harness methane fron swamps and marshes? there must be plenty of it.

If it turns out to be cheaper than coal it might be a 'good' thing, but that would mean we would most likely just burn both. If its going to be released eventually anyway, I would rather it be burnt to CO2 than as the CH4 it currently is.

Would make a lot of ammonia though (Haber/Bosch)

"...forests disappearing at a rate of 4% per year."

That seems like a fast rate to me. If Rwanda can find other sources of energy than wood, they might be able to preserve their forests. Using this methane, solar, wind, biomass, geothermal and other techniques would help.

Yes - its catastrophically fast - and the sort of thing that could lead to another round of genocide one day if they can't develop alternatives.