A sequencing batch reactor enables the same reactor to treat solids with a longer retention time while the liquid portion has a shorter retention time [86,87]. The advantage of ASBR is that it treats more substrate per unit time compared to conventional reactors. The high nutrient/microorganism ratio initially allows high substrate degradation rates and more biogas production [86-88]. These characteristics make the ASBR technology particularly suited for the treatment and recovery of biogas from high water content animal waste that would require extremely large volume digesters [87-90].
Buoyant Filter Bioreactor (BFBR): The BFBR reactor has been developed for treating wastewater with high lipid content. The reactor utilises a granular filter bed made of buoyant polystyrene beads. There is no filter clogging in this system due to an automatic backwash driven by biogas release, which fluidizes the granular filter bed in a downward direction. During filter backwash, the solids caught in the filter are reintroduced into the reaction zone and mixed again with the components. This process has no influence on the hydraulic retention time in the reactor.
The anaerobic film expanded bed (AFEB) process: The AFEB process includes inert, sand-sized particles which expand as a result of the upward direction of recycle flow. The inert particles provide a large surface (as the particles are small) for the growth of micro-organisms. The AFEB process is a completely-mixed system and provides excellent contact between micro-organisms and substrate. The micro-organism can be kept for a long period in this system [91].