AEROBIC DIGESTION

The digestion process is one of the most important sludge management practices used for sludge stabilization in wastewater treatment plants. Of these practices, aerobic digestion is the most widely used stabilization process in plants with average flows less than 5 MGD. Aerobic digestion is the process of oxidizing and decomposing the organic part of the sludge by micro-organisms in the presence of oxygen. Aerobic digestion produces a stable Class B product, reduces mass and volume, and reduces pathogenic organisms and has some key advantages for smaller plants when compared to anaerobic digestion such as low capital equipment cost and simple operational control.

 

PROCESS DESCRIPTION

Aerobic digestion is similar to the actived-sludge process. As the supply of avaible substrate is depleted, the microorganisms begin to consume their own protoplasm to obtain energy for cell maintenance reactions. When energy is obtained from cell tissue the microorganisims are said to be in the endogenous phase. Cell tissue is oxidized aerobically to carbon dioxide, water, and ammonia. In actuality, only about 75 to 80 percent of the cell tissue can be oxidized, the remaining 20 to 25 percent is composed of inert components and organic compounds that are not biodegradable. The ammonia is subsequently oxidized to nitrate as digestion proceeds. Nonbiodegradable volatile suspended solids will remain in final pruduct from aerobic digestion. Considering the biomass wasted to a digester and formula C5H7NO2 is representative for cell mass of microorganism.

In aerobic wastewater treatment systems, micro-organisms feed on organic materials to stabilize them, and reduce biological oxygen demand and suspended solids in the wastewater.  We can provide you with an aerobic digestion system for your sewerage treatment operation or combine it with one of our wastewater technologies to meet your specifications.

Typical cross section through a high-rate, gas-mixed cylindrical digester:

Mechanical stirring systems commonly use how-speed turbines or mixers. In both system, the rotating impeller displaces the sludge, mixing the digester contents. Low-speed turbine systems ussualy have one cover-mounted motor with two turbine impellers located at different sludge depths. A low-speed mixersystem ussualy has one cover-mounted mixer. Mechanical stirring system are most suitable for digester with fixed or floating covers.

Most mechanical pumping systems consist of propeller-type pumps mouted in internal or external draft tubes, or axial-flow or centrifugal pumps and piping installed externally. Mixing is promoted by the circulation of sludge, Mechanical pumping systems are suitable for digesters with fixed covers.