Polyethelene Tube Digesters, also known as balloon biogas plants,[1] are a type of biodigester quickly gaining popularity in applications throughout the world. Due to their simple construction, easily understandable mechanics, widely available inexpensive material, and versatile structure, polyethylene tube digesters are ideal for initial "test" conversions in small-scale applications.[2]
A polyethylene tube biodigester is typically characterized by a raised inlet trough, a long, flexible fermenting reservoir with a gas vent tube, and a slurry output.
The exceedingly simple design and low cost of a PET digester and its lack of moving parts means that the system is inherently reliable and cost effective. However, the design may be short-lived in comparison to more traditional digesters (e.g. Fixed dome digester, Floating drum biogas digestor) due to its construction from polyethylene plastic, which will degrade over time. However, the low cost and easy installation of the digester bag means that the main chamber is simple to replace in the event degradation begins to affect the system's performance. Though the gas inside is being pushed out only by the pressure of the other methane gas inside the digester, the flexible reservoir allows the flow rate to be modified simply by applying additional pressure to the bag- say by placing a rock on it.[3]