Anaerobic biological process in which the 0biomass converting organic matter into biogas which composed from Methane and CO2. Unlike, aerobic wastewater treatment the process is being carried out in in the absence of oxygen. Anaerobic WW presents several advantages as production of green energy source, low amounts of excess sludge and lower energy consumption. Anaerobic wastewater treatment is mainly being implemented for treatment of highly loaded COD wastewater. The Downflow Anaerobic Carries System (DACS) is an innovative technology the turned the common anaerobic wastewater treatment market upside down.