Fig. 1.

Different bioreactors for anaerobic digestion: a) anaerobic sequencing batch reactor (ASBR), b) continuous stirred tank reactor (CSTR) in a two-stage system, c) anaerobic plug-flow reactor (APFR), d) bioreactor with sludge retention system, e) up-flow anaerobic sludge blanket (UASB) bioreactor, f) up-flow anaerobic solid-state (UASS) bioreactor, g) anaerobic baffled reactor (ABR), h) anaerobic fluidized bed reactor (AFBR), i) horizontal-flow anaerobic immobilized biomass (HAIB) bioreactor, and j) anaerobic membrane bioreactor