This may be the simplest and most effective components of all of the off-grid systems we will install at El Espino but it is also a misunderstood bit of sustainable infrastructure. Different from a septic system, a biogas system or bio-digester is an anaerobic system by which solid waste (from toilets and food scraps from kitchens) is collected in a tank and over the course of a few weeks is converted into a clean and safe slurry rich in nitrogen, phosphorus, and potassium. The slurry is output to a simple distribution system and used as fertilizer on trees and non-food plants. Methane gas is also produced within the anaerobic process. The gas will be captured and burned for heating water.
The “input” process from the toilets is no different than any other flush toilet; toilet paper can be flushed too and will be broken down in the process. Water, input into the tank along with solids, helps to break down the solids and accelerates decomposition. While a little icky to consider, a well-managed biogas system is an essential component in the lodge’s successful operations and commitment to sustainability.
Here is an article with helpful photos describing a system in Costa Rica: http://www.ruralcostarica.com/biodigester.html
Here is an overseas supplier of systems with helpful descriptions and illustrations: http://www.avenamlinks.com/index.php/products/