substrate being treated or converted during startup of the contactor reactor the reactor would be treated as a single stage batch system that is to say the reactor would be filled with substrate feedstock and a mixed population of bacteria from another process sewage sludge digestion for example would be used to seed the reactor in the conventional manner as soon as the consortia had established itself and methanogenesis was occurring fresh substrate would be introduced at the input end of the reactor at the same time zonal sludge recycling would commence in this way different classes of consortia would develop in different zones along the length of the reactor naturally the rate of zonal sludge recycling and the length of the zone may be varied to establish optimal conditions for the type of substrate to be treated or converted the reactor substrate is by no means limited to wastes substrates may be complex organic material s feedstock which requires converting to simpler or specific compounds liquid is transferred from compartment to compartment in the classical graesser manner the same holds for solids transfer of liquids from the end to the beginning of the zones would be carried out by pumps or similar variable mass transfer devices not shown the end product of the effluent will be dependent on the substrate with some substrates further treatment may be necessary further downstream processes may.