Anaerobic–aerobic systems have been remarkably employed in industrial and municipal wastewater
treatment for many years. While previously most treatment of wastewaters have been carried out in
conventional anaerobic–aerobic treatment plants, in recent years, high rate anaerobic–aerobic biore-
actors have been increasingly employed for wastewaters with high chemical oxygen demand (COD).
This paper provides a review of the various types of high rate anaerobic–aerobic water treatment tech-
niques currently available including high rate bioreactors and integrated anaerobic–aerobic bioreactors.
The integrated bioreactors are classified into four types, which are (i) integrated bioreactors with phys-
ical separation of anaerobic–aerobic zone, (ii) integrated bioreactors without physical separation of
anaerobic–aerobic zone, (iii) anaerobic–aerobic Sequencing Batch Reactors (SBR), and (iv) combined
anaerobic–aerobic culture system. The integration of aerobic and anaerobic degradation pathways in
a single bioreactor is capable of enhancing the overall degradation efficiency. The merits of different inte-
grated anaerobic–aerobic bioreactors are highlighted and comparison made to identify possible future
areas of research to fully utilize these methods of wastewater treatment. The comparison demonstrates
that using an integrated bioreactor with stacked configuration in treating high strength industrial wastew-
aters is advantageous due to minimal space requirements, low capital cost and excellent COD removal
efficiencies (in excess of 83%).