What I did while I was lost in equation

Powered by Poop: Turning waste into wealth in a sustainable Iceland.



Introduction: Everyone poops.

Taro Gomi’s classic toilet-training book proudly proclaims that “everyone poops”. So we do. Every animal and we are animals, produces solid waste in the form of feces. Nothing earth-shattering or earth-changing there. However, when one starts to examine what we do with the poop everyone makes, things get a bit more interesting.

In the Western world, poop is a taboo. Up until the early 1980’s for instance, American TV shows where more or less banned from showing toilets in the homes of their fictional inhabitants, leading to the surreal home of the Brady family, with 8 people living in a home with no waste disposal. No toilet, no outhouse, nothing.

This wasn’t always the case of course. Poop, particularly livestock manure, has been a terribly useful substance in times past and in many places remains so. Aside from being the original organic fertilizer, it was dried and burnt as fuel, mixed with clay and straw to form wattle, still a common building material throughout Africa.

Today, with the world teetering on the brink of Peak Oil and in the midst of a major economic depression, another of those old uses for poop, namely converting said material to methane[1] a colorless, odorless (contrary to popular belief) lighter than air flammable gas, deserves a serious look.

Processing Poop.

The process of converting animal waste into methane is a relatively simple one, not much more complicated than brewing beer or distilling alcohol. There are two basic methods; batch digesting and continuous digesting, each of which is suited to certain situations.

Batch digesting works best on sheep, horse, dairy, and beef farms. To begin with a digester (usually more than one) is made by converting a liquid manure-spreader like the one pictured below.

The conversion consists of fitting the spreader with a vent and coupling to release the bio-gas (unfiltered methane along with some CO2 and other gases), a heat element attached to a thermostat (usually a radiator) inside the tank and a layer of insulation outside to maintain the necessary temperature (25-30˚C) and an agitator (think big blender) powered by the steam exiting the radiator to keep the slurry (mixed waste and water) from settling in the tank.

The farmer (let’s call him Bubba) then fills the tank with manure and water per standard procedure with liquid manure spreaders. Bubba then pulls the tank (now a “digester”) up to a storage tank (of which there are several designs, the cheapest being a gravity tank like that pictured below).

Biogas then feeds from the tank through a series of filters that help eliminate water vapor, CO2, and stinky sulfur dioxide, leaving purified (90%) methane. Once the slurry has been thoroughly digested, the digested slurry (now called sludge) is then spread on the fields as per usual. Meanwhile, a second tank is being filled, and ready to attach to the storage tank.

Continuous digestion works in a similar manner, but instead of filling one tank while emptying the other, several tanks are linked in series, so that by the time the slurry flows out as sludge, its been thoroughly digested. This design is more costly, but works very well for factory (chicken and pig) farms, as well as for converting human waste.

In both systems the slurry is broken down by anaerobic bacteria, leaving behind a nearly odorless enriched sludge suitable for use as fertilizer.

The Scoop on Poop.

While it may be true that “everyone poops”, not all poop is created equal. Some animals produce a lot of it, others considerably less. Likewise, when it comes to the methane that can be produced from poop, there are noticeable differences. As a general rule, ruminants (that is grass-eating animals) produce more poop, and the poop they produce is a better source of methane. Poultry produces very high methane returns, but less volume. Omnivores like pigs and humans produce considerably less methane, and humans produce less than pigs. Carnivores produce the lowest amounts of methane per kilo of poo, and for that reason (as well as the fact that fur farming has been decreasing year by year for the last few decades) it isn’t really worth including them.

The following chart based on numbers from Engines for biogas[2] shows the average daily output of several commonly raised domesticated animals in British Thermal Units (Btu) a measure of thermal energy roughly equivalent to burning one match:

Daily Btu output per animal

(Rounded to the nearest whole number):

1. Cattle (Dairy/Beef): 7148 Btu/day
2. Poultry: 36 Btu/day
3. Swine: 3597 Btu/day
4. Horses: 6949 Btu/day
5. Sheep/Goats: 1986 Btu/day
6. Humans: 596 Btu/day

According to the most recent census by Bændasamtök Íslands (The Icelandic Farmer’s Association)[3] the live stock population is as follows:

1. Dairy Cattle: 25,504
2. Beef Cattle: 41,466
3. Poultry: 181,857
4. Swine: 4,218
5. Horses: 75,644
6. Sheep/Goats: 455,656

The human population (according to most sources) is:

7. Humans: approx 320,000

So following the formula (number of animals) x [Btu/day x 365] we get the following results for Iceland in trillions of Btu.

1. Cattle (Dairy/Beef): 0.17 trillion Btu/year
2. Poultry: 0.02 trillion Btu/year
3. Swine: 0.05 trillion Btu/year
4. Horses: 0.19 trillion Btu/year
5. Sheep/Goats: 0.33 trillion Btu/year
6. Humans: 0.69 trillion Btu/year

This gives us a total of 1.45 trillion Btu/year produced from animal waste. However, this number is only a rough estimate, as average methane production reports vary (I went with some extremely conservative numbers). Also while most of the cattle (sheep, goats, horses, beef cattle, and dairy cows) spend a great deal of their time out of doors, and hence leave poo littered all about the fields as opposed to on the barn floor, the Icelandic populations could spend more time indoors due to inclement weather than their Southerly cousins, leading to increased returns.

To put this in perspective, the U.S. Energy Information Administration (EIA) reports that Iceland consumed 20,080 barrels of petroleum fuels per day. So to crunch the numbers that’s 7,329,200 barrels of primarily petrol and diesel a year at an average of 5,523,000 Btu per barrel meaning that Iceland consumes about 40.5 trillion Btu a year[4]. Hence Iceland could replace 3.5% of its current petroleum use with renewable methane from animal waste alone. This is not, as it might first seem, chump change. The total livestock methane output for the U.S. if converted would be no more than perhaps 1%.

It’s worth keeping in mind that municipal organic waste (otherwise known as garbage) can also be processed into methane. Currently Metan hf. is the only company in Iceland exploring this option According to CEO Björn H. Halldórsson Metan’s yearly out put is between 0.076 and 0.1 trillion Btu per year.[5] Splitting the difference and adding those 0.88 trillion gives us approximately 2.33 trillion Btu or 5.7% of Iceland’s current consumption. It’s also worth keeping in mind that Metan is only one operation, operating only in the capital area. If every municipal landfill in Iceland was tapped for methane, we could very well see the total number go up to 7-8%. Finally, I did not include the conversion of “green matter” (old straw, vegetable scraps, plant trimmings etc.) and organic waste from ethanol production, but such wastes could provide another substantial addition to methane production.

One man’s shit is another man’s gold

So getting down to brass tacks, what would this mean to Bubba the farmer? Well, assuming he lives on a farm with his wife and two children, 300 sheep, 10 cows, and perhaps 3 horses, and he puts all the poop into a digester, he would get approximately .00021 trillion Btu. In practical terms, this is equivalent to 5753 liters of diesel fuel. Now assuming that Bubba has an older tractor, eating up fuel at a rate of 30 liters per hour of operation, this means that he can run his tractor for 191 hours or roughly 8 days, or drive his car (assuming it consumes something like the average of roughly 10 liters per 100 kilometers) 57,530 km. All on fuel produced at home. Assuming that 5753 liters of diesel costs roughly 863,000 ISK at retail prices, the benefits for Bubba are clear.

Producing the fuel at home has another hidden benefit, namely that no fuel is expended shipping said fuel out to Bubba’s farm. If every farmer in Iceland converted their poo to power, the net savings in petroleum used in shipping petroleum would be impressive, as would the reduction of greenhouse gasses. This is due not only to less petroleum being burned to ship other petroleum out to Bubba’s farm, but also due to the fact that much of the methane captured in Bubba’s digesters would have leaked into the atmosphere anyway, and methane is 20 times the greenhouse gas that CO2 is.

As for factory farms and municipalities, the picture is a tad murkier. After all, a small city with a population of 4,000 (Ísafjörður for instance) would only produce about .0009 trillion Btu. However, the fuel produced would likely be enough to power a few buses, fire-engines, and ambulances. As an added benefit, just digesting the municpal slurry would be an improvement on the generally woeful state of Icelandic sewage treatment. In many municipalities around Iceland, sewage is pumped out to sea with little or no treatment at all. Digesting it for methane would improve, however slightly, the situation.

But wait, there’s more.

If Iceland really wanted to clean its municipal sewage, and reap a major energy reward in the process, they should look no further than the broadleaf cattail (Typha latifolia) a hardy perennial plant common throughout the Northern Hemisphere. While this incredibly undervalued plant has a myriad of uses, only two (or maybe three) concern us here, namely its ability to thrive on waste water while cleaning it, and the fact that when ripe it can be as much as 60% starch. Allowing digested sludge to flow through an artificial wetland planted in cattails would not only lead to much cleaner emissions entering coastal waters, but could yield as much as 3,784 liters of ethanol fuel per acre or 117,304,000 Btu.[6]

Cattails spread via a long underground root called a rhizome, which along with the lower stalk of the plant contain most of the starch. Because they spread via rhizomes, they can be contained in concrete lined troughs, with no danger of going feral via seeds. Once harvested, these plants could then be fed through a shredder, and immersed in a tank of warm water. An enzyme that breaks down the fibrous cellulose is then added, along with malt enzyme (the same substance used to break down cereals for brewing beer and whiskey) and placed into a fermentation vat where yeast break down the sugars, producing ethanol, which is then distilled (using the same heat source that heats the slurry) filtered, and put into a car. If the cellulose is simply skimmed off, it can be put to productive use closing the poop loop, namely producing that necessity of necessities shown below.

The organic matter left over from the fermentation process can then be cycled through the biogas digester. In other words, the poop loop gets closed.

From “prump” to pump.

Because of the Western taboo when it comes to crap, “poop power” is going to be a hard sell. After all, people are loath to think that the waste from fuel exiting their car’s tailpipe was once the waste from fuel that exited their own. But when viewed in a rational light, the benefits are so enormous as to outweigh bourgeois squeamishness once and for all.

What benefits? Aside from the marked increase in water quality that would result from treating municipal waste in the manner mentioned above, and the decrease in greenhouse gases concurrent with methane production, every non-electric car, truck, boat, and motorcycle on the road or on the sea in Iceland today can be converted to run on either ethanol (which was Henry Ford’s fuel of choice for the Model T[7]) and/or methane by installing a conversion kit. Essentially this means altering the carburetor (which blends fuel and air to the correct proportions) and installing a compression tank for the methane. Diesel engines require replacing the glow-plugs (which provide heat to help ignite the fuel) with spark plugs if converted to run on methane. This not only saves the consumer the price of buying an entirely new vehicle, but also cuts drastically down on the energy and materials consumed to manufacture a new fleet of vehicles.

This being said, powering Iceland with poop is only part of the solution, especially when you consider the woeful state of my math skills. Methane could only account for 5% of Iceland’s current consumption. Also methane doesn’t compress well making it hard to transport. This means that long-distance vehicles wouldn’t work very well on methane unless they were able to re-fuel on a regular basis. But with methane being produced on most farms and in most small towns around the country, this wouldn’t be a problem. If the methane is used to power farm equipment the point becomes moot, as any equipment would be operating very close to its source of fuel. Ethanol doesn’t have the same draw backs, but it’s unlikely that Iceland would ever be able to produce the equivalent of 40.5 trillion Btu that it currently consumes. So we are left with reducing that number.

Electric vehicles, in particular rail could help bring that number down considerably although they will still have very high embedded energy costs. Another method would be to work at increasing the efficiency of internal combustion engines by pairing them with good old fashioned steam power to produce mechanical hybrid engines. Internal combustion uses the explosive force of burning fuel; the heat is mainly a waste product. Meanwhile steam engines use the heat, but fail to capture the force of expanding gases. Considering that both types of engines have similar mechanics (pistons or turbines) the solution is out there. We just need a few enthusiastic engineers to figure it out.

An Iceland free from dependence of fuel imports would be more prosperous, as the drain on the national coffers would melt away. It would also be more secure, as short or long term trade disruptions would not have as much impact. Likewise, the decentralized nature of the production and decrease in transport of these fuels would lower the over all severity of accidents. One storage facility wouldn’t be able to blow up an entire neighborhood, and the loss of two production sites wouldn’t leave the nation with naught but shoes and bikes to travel by. Finally the “waste” from methane digestion is enriched fertilizer, allowing for increased domestic food production, which is an important goal to strive towards for a small and geographically isolated island nation like Iceland. Additionally the monetary savings resulting from domestic fuel and fertilizer production would go a long way towards balancing Iceland’s trade deficit.

All in all, poop power is an idea whose time has come. In the American vernacular, it’s high time we shit or get of the pot.