Numerous biodigester designs exist for processing and/or treatment  of organic waste streams with solid contents of less than 5 % and highly specialized designs are available for treatment of waste streams with less than one percent total solid content. These types of digesters typically employ mechanical mixing apparatus.

Hydraulic digesters that simulate a cows anaerobic stomach more closely are capable of processing complex, relatively high density (5 to 15 % solid content) organic waste streams such as manure reliably and efficiently. Substrates such as poultry manure are typically diluted to 15 % total solid content prior to processing. 

Developed during the 1970s and early 1980s, multiple designs exist. We prefer a dual chambered design for continuous mesophilic true anaerobic operation. It completely eliminates the possibility of partially digested effluent leaving the digester. Separate take-offs for biogas, digested effluent as well as sediments ensure continuous trouble free long term operation. Mixing occurs due to equalization of a pressure differential buildup between the two chambers without moving parts, eliminating mechanical maintenance, mechanical failures as well as energy consuming mixing apparatus. All fresh substrate entering the digester is immediately "inoculated" with bacteria and slightly alkali digested substrate, minimizing the possibility of the digester going sour. This also makes the design ideally suited for use with co-substrates. 

Since only fully digested substrate leaves the digester, reduction of odourous compounds is maximized. All methane is harnessed, significantly reducing or eliminating GHG emissions normally associated with organic waste processing.

Hydraulic designs also have an advantage as far as internal energy consumption is concerned. They typically use approximately 30 kWh thermal energy per metric ton of substrate even in Canadian climate conditions. Since there is no mechanical mixer in the digester, electricity is required solely for control systems and feeder pumps. 

These requirements are typically in the range of 2kWh el. per metric ton processed. Net surplus of at least 85 kWh energy per metric ton of processed organic substrate can be expected. 

Addition of co-substrates for an optimum overall substrate mix with 15% solid content substantially increases biogas production and energy surplus. 

Hydraulic Retention Time of substrate varies depending on precise temperature control. At mesophilic temperature we can expect a retention time of between 20 and 30 days. Reactors ranging in size from 100 to 8000 m³ have been built with a better than 20 year lifespan.

RENTEC is currently completing construction on its own next generation design due to be operational at the end of 2006. - animation soon to follow.