Components of Plug-Flow Digester
A plug-flow digester system generally includes a mix tank, a digester tank with heat exchanger
and biogas recovery system, an effluent storage structure, and a biogas utilization system. Post
digester solids separation is optional.
Collection/mix tank. A mix tank as described above for a complete digester is used to achieve a solids
concentration between 11% and 14% solids.
Plug-flow digester. A plug-flow digester is a heated, in-ground concrete, concrete block or lined
rectangular tank. The digester can be covered by a fixed rigid top, a flexible inflatable top or a floating
cover to collect and direct biogas to the gas utilization system.
Biogas utilization system. The recovered biogas can be used to produce space heat, hot water,
cooling, or electricity.
Solids separator (optional). A mechanical separator may be installed between the plug-flow digester
outflow and the effluent storage structure.
Methane recovery system. A plug-flow digester is covered by a gas tight fixed solid top, a flexible top,
or a floating cover to collect and direct biogas to the gas utilization system.
Solid cover. A solid cover is constructed to avoid cracking and leaks. Solid covers should resist
corrosion. A solid cover allows for minimal gas storage.
Inflatable Cover. A coated fabric is generally used for inflatable covers. An inflatable cover can be
designed for some gas storage. Wind protection may be necessary. The cover must have a gas tight
seal.
Floating cover. A floating cover is designed to lie flat on the digester surface.