Tube Gas Digester

The tube gas digester is a low-cost tubular plastic digester. It was developed by CONDRIT (Consultorias el para el Desarrollo Integrado del Tropico) in Cali, Columbia, in the early 1980s. The digester was based on a design first found in Taiwan, a Mud PVC biogas digester.

The cost of the tube gas digester is relatively low, varying according to size and location. For instance, the price per m3 of liquid volume in Colombiais around $US30. Pretty cheap, considering this includes the container and its connections. Plus cement boxes for the inlets and outlets, a plastic gas reservoir, a stove, and labour to prepare the trench and installation of the biodigester.

The average cost per square metre in Vietnam is around $US7 (materials only). The total cost for one biodigester of 5.4 m3 of US$37.80, including two burners. In Western countries, the cost polythene tubes are also relatively cheap.

Although the design is straightforward, you must dig a trench to receive the tube gas digester. Trench walls must be firm, and the floor must be flat or with only a minimum slope. There must also be no sharp stones or protruding roots in the bottom, which might perforate the tube gas digester. Long tubular polyethylene used in agriculture is available in most countries.

Often local availability limits the choice of fittings and materials. You will have to work with whatever is on farms or in rural markets. Improvising is the key, for example. We made a simple safety valve from a transparent plastic bottle, a T-piece and 3 PVC tubes (one 6cm and the other two of 30cm). Water is poured into the bottle to a 5cm depth above the mouth of the tube. All these details are in the construction plans. Plans for the construction of various systems are available to download for free in the Construction section of the site.