Aerobic and facultative phases of biological treatments for sewage

Biochemical treatment CAN be divided into aerobic biochemical treatment and anoxic biochemical treatment according to the different requirements of microbial growth on oxygen environment, and anoxic biochemical treatment can be divided into concurrent oxygen biochemical treatment and anaerobic biochemical treatment.

According to the different requirements of microbial growth on oxygen environment, biochemical treatment can be divided into aerobic biochemical treatment and anoxic biochemical treatment. In the process of anaerobic biochemical treatment, aerobic microorganisms must grow and reproduce in the presence of a large amount of oxygen, and reduce the organic matter in wastewater.  However, in the process of facultative oxygen biochemical treatment, facultative oxygen microorganisms only need a small amount of oxygen to grow and reproduce and degrade organic substances in wastewater. If there is too much oxygen in the water, facultative oxygen microorganisms will not grow well and thus affect their treatment efficiency of organic substances.

Facultative oxygen microorganisms can adapt to the wastewater with high COD concentration. The influent COD concentration can be increased to more than 2000mg/L, and the COD removal rate is generally 50-80%.  However, aerobic microorganisms can only adapt to the wastewater with low COD concentration. The influent COD concentration is generally controlled below 1000-1500mg/L, and the COD removal rate is generally 50-80%. The time of both concurrent and aerobic biochemical treatment and aerobic biochemical treatment is not very long, generally within 12-24 hours.

People make use of the difference and the same length between facultative oxygen biochemistry and aerobic biochemistry to combine facultative oxygen biochemical treatment and aerobic biochemical treatment, so that the wastewater with higher COD concentration is first treated with facultative oxygen biochemistry, and then the treated effluent of facultative oxygen tank is used as the inlet water of aerobic tank. Such combined treatment can reduce the volume of biochemical tank.  It not only saves the investment of environmental protection but also reduces the daily operation cost.  The principle and function of anaerobic biochemical treatment and facultative aerobic biochemical treatment are the same.

The difference between anaerobic biochemical treatment and concurrent oxygen biochemical treatment is that Anaerobic Microorganisms do not need any oxygen in the process of reproduction and growth and organic material degradation treatment, and Anaerobic Microorganisms can adapt to higher COD concentration of wastewater (4000-10000mg/L).  The disadvantage of anaerobic biochemical treatment is that the biochemical treatment time is very long, and the residence time of wastewater in the anaerobic biochemical tank generally needs more than 40 hours.