A quick pictorial of the biodigestor

I mentioned in an earlier post about helping a couple families build biodigestors and gave a basic overview of what it is and how it works. I took some pictures of the basic setup so that you all might get a better concept of how it all works.

1. On the left are the stalls where cows are kept. The floor was built on a slight slope to aid in cleaning. All the waste and water is washed into the first catchment and then continues to the next two barrels. This is a system an ag. extension agent here recommended. I have never used these additional barrels, but he said that they help in filtering the water since cows track in a lot of sediment and dirt which would otherwise settle in the bottom of the biodigestor bag and make it fill up quicker than necessary. I have my doubts about it since I feel like we are losing a lot of precious poop, but time will tell.

These are the barrels, one is still missing a top. From there the mixture goes to the biodigestor bag..

This is the bag. A trench is dug so that the bag is about halfway in the dirt. Two cement tubes are placed at each end at an angle with the ends above ground level (the big opening you see is a cement tube with plastic around it). The bag is filled with the mixture daily. The mixture stays at a fixed level (ground level) and when new poo is added the exact same amount is pushed out of the bag at the other end through displacement. What comes out is good, but strong, liquid fertilizer.

In the middle of the bag on the top is a hole connected to piping. Since the bag is devoid of oxygen , anaerobic decomposition occurs and the bacteria in the mixture create methane. As the bag fills pressure rises and gas is pumped out of the hole easily. It goes through a water filter (plastic bucket you see after the green piping) to clean out any impurities and then goes right to the house for use in the kitchen.

And that's basically the setup for a biodigestor. There are different ways of doing it such as a cement or brick tan with half bag on top, but this method shown above is the cheapest and most accessible here in Costa Rica.