Wastewater contains energy in the form of biodegradable organic matter. The concept of
accomplishing wastewater treatment and generate energy simultaneously has been a trend recently and
can be done with hybrid wastewater treatment system. Energy gained from such hybrid system is
therefore both sustainable and environmental friendly which may be good source of bio-energy to
compliment the power of a treatment plant. In this paper, we classify hybrid wastewater systems
typically include physical–biological hybrid, physical–chemical hybrid, chemical–biological hybrid and
physical–chemical–biological hybrid system