ABSTRACT
As the conditions become anaerobic, plant and animal life in the water die, and anaerobic bacteria are able to grow, producing foul odors. In comparison with aerobic treatment, anaerobic treatment has the disadvantage of being slower, but the advantage that fewer new bacterial cells are produced. Instead, some broad concepts and techniques will be described since they form the basis of most treatment methods. Complete treatment can sometimes be achieved in shallow aerobic lagoons, but a common system consists of a primary anaerobic basin followed by aerated or aerobic lagoons. In practice, oxidation ponds are often used after anaerobic lagoons to "sweeten" the effluent prior to discharge into the receiving water. Aerobic processes have the advantage over anaerobic processes of providing faster Biochemical Oxygen Demand. In contrast, anaerobic processes produce methane gas, which can be used as a fuel, and this can help to offset the operating costs of these systems.
