Developing a biofertilizer drying system

Guest post by summer technical intern Jacob McEntire

The biogas systems that we construct not only allow our clients to save time and money on fuel, they also produce a very effective and natural fertilizer once the animals waste has decomposed and let off the biogas. Many farmers in the regions we work keep both animals and farm crops. These crops at times go without fertilizer, others are treated with an expensive chemical fertilizer or cow dung direct from the cow shed. If you have been keeping up with us, you may have heard about a particularly innovative fellow, Henry Ritho, who has a Takamoto Biogas system and has been experimenting with the biofertilizer since installation which resulted in more than doubling his corn (maize) crop grown on stalks twice his height.

So, now that we have people thinking about the benefits of biogas – free, reliable, safe, easy, clean house, clean lungs etc – let’s get talking about the benefits of biofertilizer and thinking about creating a system to use the biofertilizer that is as simple to use as the systems we build to make the biogas. Jacob took on this task whole-heartedly and developed the system described below.

NAIROBI—Hello all!  Jacob here again to give you an update on my work with the fertilizer drier system (which I am now calling a separator system).  The premise for the system is simple: it is designed to separate the liquid and solid components of the biofertilizer that biogas plants produce.  I mentioned in my last post that this makes transportation easier for farmers who have a long way to haul their fertilizer, but it can also encourage the sale of the fertilizer, as packaging is also much easier when you’re dealing with either a pure solid or a pure liquid.

The system comprises layers of ballast and sand contained within a watertight case and laid at a slight angle to direct the liquid effluent into a holding tank.  This was all topped off with a layer of wire mesh to provide a soild top to the bed part of the system.  The first model was implemented at the farm of Joakim Mbuthia in Muguga.

The mark I performed adequately, but had several design flaws.  Namely the wooden base and siding were too thin to hold together well – the nails that were used during construction split the thin wood in some places, which meant that the system as a whole was not strong enough to withstand the weight of the ballast and sand, and ended up fracturing when they were poured in.  In addition, the slope was too steep (maybe 3 inches down for every foot across) to have the top of the system be level.  This meant that effluent would sometimes run down the sand and wire when poured on, instead of sitting on top.

The mark II (installed at Henry Ritho’s farm in Kangema) fixed most of these problems.  By forgoing the wooden base and siding in favor of a packed-earth pit lined with polythene sheeting, we were able to simultaneously ensure that the system would not break, and make it more watertight.  We also made the slope less steep, ensuring that effluent would sit on top as intended instead of running off.  Finally, we fashioned a cover from logs and more polythene to protect the effluent inside from the rain and sun that would inevitably come.

While I have high expectations for our second design, it has been less than a week since its installation, so I will have to wait and see whether or not it lives up to them.  It is also important to bear in mind that the mark II took advantage of the elevation at Henry’s shamba (farm).  The question if it works will be: how do we translate this design into something that can be implemented anywhere?