Today we finally reached Gorak Shep! I ate a lunch of hashbrowns with cheese and an egg in under two minutes. Anyway, sitting at 5,140m drinking tea with my guides in the sunshine, I was all smiles.
Once we had our things settled, we set out to view the two digester sites Mingma had previously considered. The first was to the North East of Gorak Shep, at the end of the dry lake bed. This spot is a good choice because it is off the beaten path, has good solar exposure and is near a shelter used by waste porters. However, since the wind blows from the South along the lake bed, any solar panels there would get dusty. When dust accumulates on PV panels their efficiency decreases, since the dust film reflects the sunlight before it can enter the cells. Also this site is to the South of the mighty hill Kala Patar. This scenic hill, that trekkers climb to photograph the surrounding mountains, would block the sun some of the time. Plus one never knows when a randomly bumped rock, will find a chaotic path down to your solar array.
On our way to seeing the second site, we stopped to chat with two porters carrying down the human waste from base camp. It seems that now, the pit that receives the waste is another two hours walk below Gorak Shep. The waste issue here will only get worse, along with the ground water quality in these habitations and along the glaciers.
We walked up to the main porters’ shelter, and Mingma showed me the second site he had scouted. The solar potential there is great, away from the shadow of Kala Patar and upwind of the dry lake. It is also close to the porters’ kitchen, which would allow us to directly tie the gas-line from the digester into their stove. Best of all, the site is a wash that never has streamflow through it. It is filled with some boulders, in dry sand! Sand is very stable to build upon, once it has been consolidated. But more importantly, the voids between the sand grains create small air spaces that hold heat. Such air voids are the same reason that fiberglass rolls or straw-bales make for good insulation. This is great news and I actually did a little squiggle dance of joy. So far, the technical design team has been using the heat capacity and conduction coefficients of wet soil in our calculations. This was a conservative estimate, but now that this survey has found our actual site location, we are sitting pretty on dry sand! Great news.
I have only been working on this design for about two years, but the Mt. Everest Biogas Project has been in process for more than three now. Our technical design team has already investigated the feasibility of biogas production at Gorak Shep. This entails operation at lower than normal temperatures, when only human waste is the substrate. Humans shed a lot of broken down protein, so our waste tends to have a higher amount of Nitrogen relative to Carbon. Methane is Carbon based, so you can make a lot more of it, from say, a grass eating animal’s manure. Then again, since Gorak Shep receives ~12,000 kg of human filth annually, we are going to use that. Anyway, the numbers we came up with showed you need at least ~20°C inside the digester to make methane and get through all the waste. If you can pull off keeping the digester at 30°C, then all the waste still gets destroyed, and you get a little more biogas.
The next thing we had to figure out was, how hard it is to keep a digester warm in basically 0°C ground. This is not an easy task and we investigated different possibilities of how to operate the digester. The conclusion was that, for the amount of heat loss you need to overcome, the best deal is to operate only in the warm bit of the year with the goal of 30°C. Heat loss in the winter makes year-round operation a losing proposition. Also, the smallish increase in heat loss at 30°C compared to 20°C is worth it to make more biogas. Using the goal of 30°C also means our process will be stable. Even if the digester’s internal temp dips to 20°C, we know we can still process all the waste and make biogas.
With all the givens for this problem penciled out, we could finally address the crux of the issue. What exactly is the solution that can maintain a 30°C digester at Gorak Shep, from spring into fall? If anyone is still reading, I will spare you the alternatives analysis… The technical design team has devised a system that shows such an extreme project is possible. This design, which I am in Nepal to present to our affiliate NGOs, is a feasibility design. It is not the final edit! And it will continue to mutate & evolve, based on the data and available materials discovered in this trip.
I hope that was enough caveats for any engineers reading this… Anyway, the essence of this design is to give the digester a burly coating of insulation (R-50) and then put a shed on top of it. The stabilized waste will be a liquid that can be poured into a septic tank style drain field. The shed will have a window to collect solar heat passively, and this will be shuttered at night to retain the warmth. This room will also keep the stored water & waste from becoming frozen, before it is mixed and fed to the digester. We first looked at a passive solar solution to this problem, and that will definitely not work. So additionally, we will insulate the water storage tank and put a DC electric heater in it. This means, we need solar panels to make the system work. But fortunately, Gorak Shep is no stranger to PV panels, which is how I come to be e-mailing this off to the readers at home. The heated water insures we won’t shock the digester by feeding it cold slurry. But more critically, we can keep the digester warm by pumping the hot water through a pipe network placed inside the digester’s floor. This sort of design is done in the floors of Hippie mansions and bears the name, radiant heating.
If the radiant heating system’s pump is controlled by a thermostat, we will only heat the digester when necessary. It would be a shame to cook all those happy little gas producing bacteria. What really makes this design concept robust though, is that whenever the sun is shining, we will store energy as heat inside a reservoir of water.
Water is great for this task and non-toxic! By storing heat, we can dampen the effect of sunless days. When the sun is out, the ground is warmer and the digester won’t be so troubled by heat loss. But at night or during a string of cloudy days, a system that used direct electrical heating would be useless.
So there you have it. The basic concept we will use to solve the massive human waste problem at the shoulder of the highest mountain in the world. For all you engineers out there, please trust I have left this description to a minimum. We have considered antibiotic toxicity, rate of waste delivery from base camp and all the other things you would have been cutting me off to interject if this had been a conversation. Much love, and best wishes.