Introduction
The conventional aerobic processes that are widely used for the treatment of domestic wastewater have at least three distinct disadvantages: their relatively high electrical requirement, the high operation cost and the high excess sludge production which requires treatment and disposal that further increases the operational cost.
On the other hand anaerobic processes produce methane gas that can be collected and used as an energy source in addition to the low energy consumption. The sludge production is also minimal, and additional important benefit is that the anaerobic sludge can be preserved while not being fed for long periods of time at temperature below 15 °C