As I mentioned in my last post, the Promise Home orphanage endeavors to raise large quantities of tilapia to fund its operations. Tilapia is big business here in Honduras (where I have been for the last 3+ weeks). In fact, today we had lunch a little restaurant called "La Rocca" where they pull a tilapia out of the tank for you, whack it on the head with a wooden mallet, and then fry it up! Lunch with entertainment! You get the head, fins, tail, and a side of plantains. It's not Tex-Mex, but I like it anyway.
At any rate, if you have a tilapia business you either need to drain the tank a few times per year to shovel out the poop (somebody call Mike Rowe), or build a self flushing type of tank as they did at Promise Home. Our project is to build a biogas generator to convert the fish poop into methane gas which can be used to heat water, cook, or generate electricity, for example. After the tanks are "flushed" the contents go to a sediment tank. The idea is to slow down the velocity of the water so that the "solids" sink to the bottom. That's where we come in. And I mean literally come in.
[William dons the waders in preparation to enter the sediment tank. His matching hat was not planned, just a nice coincidence.]
[He's using a sump pump to vacuum the fish poop off the bottom of the sediment tank. The water is not clear enough to see through, so you have to step around to feel where you have vacuumed and where you have not. Squishy stuff underfoot = need to vacuum.]
[The green hose was 2" in diameter which made it pretty heavy and hard to manage when it was full. We switched to a 1" black polyducto hose like the one in the foreground.]
[This is one of my favorite pictures, mostly for the gross-out factor. This is where the sump pump empties into a 600 gallon tank. It's a fountain of renewable energy! The tank is manufactured for use in collecting drinking water, and we cut the top off with a circular saw. If the tank was square, we would use a square saw. Ba dump bump. The black tank in the picture behind Tim will be inserted, upside down, onto the "fountain" and will fill up with sludge. Being inverted it will be able to collect the gas produced without leaking. It must all be kept in an oxygen-free environment on account of that's the way the bacteria like it.]
[We turned the pump off after about 500 gallons. Later we added a little lime water to control the pH levels and a triple dose of Rid-X Septic Tank treatment to try and jump start the bacterial growth. Make my coffee a Rid-X triple shot low fat mocha with calcium carbonate sprinkles, por favor.]
Here's how it works. First, a class of bacteria called Acid Forming bacteria break down the complex organic molecules into fatty acids. Then a second class of bacteria called Methane Forming bacterial eat these acids and produce methane gas (CH4) as a byproduct. This is the same gas that we commonly refer to as "natural gas" and it can be burned in any of the same appliances such as burners, electric generators, etc.. For the last week or so, we have been monitoring the gas output, but it hasn't been the mother load of biogas that we had hoped for. In fact, it's been just a trickle. We're not sure what's wrong, but we know sometimes it can take weeks to get stabilized. Stay tuned for more news on the fish-poop-to-renewable-energy project of the century! Cue fish poop music in your mind.