Читать книгу Encyclopedia of Renewable Energy - James Speight G., James G. Speight - Страница 193

Aerobic digestion is the biochemical oxidative stabilization of wastewater sludge in open or closed tanks that are separate from the liquid process system. Aerobic digestion is a solids stabilization process that provides a limited supply of oxygen to microorganisms in order to facilitate oxidation of organic matter and convert it into carbon dioxide and water. The microorganisms utilized in aerobic digestion processes are mesophilic facultative bacteria which mean they thrive in temperatures between 20 and 37°C (68 and 100°F) and live under aerobic (presence of oxygen), anoxic (no oxygen but with presence of nitrates), and anaerobic (no presence of oxygen or nitrates) conditions. Thus, the aerobic digester operates on the principle that as the food is depleted, the microbes, the endogenous phase, and the cell tissue are aerobically oxidized to carbon dioxide, water, ammonium ions (NH⁴⁺), nitrite ions (NO²⁻), and nitrate ions NO³⁻).

In general, aerobic digestion is a relatively simple process; there are many design and operational parameters such as temperature control, oxygen transfer and mixing, nitrification and denitrification, solids retention time, pH control, sludge loading characteristics, and tank configuration that must be considered in order to achieve a sustainable process.

Typically, an aerobic digestion system consists of two or more aerated tanks used to process and store waste-activated sludge generated from the liquid treatment process and/or primary sludge from primary sedimentation tanks. The waste-activated sludge and primary sludge in an aerobic digestion system can be processed separately or can be combined into one product. Air is introduced to the tank(s) from an aeration system typically coarse or fine bubble diffuser equipment with the air being supplied by a positive displacement or centrifugal blower.

The bacteria continue metabolism as they do in the liquid process, but without new food, they use their own biomass (endogenous respiration). This stabilizes the sludge so that it is safer for human contact, does not attract vermin (vectors), and odors are reduced. This method of digestion is capable of handling waste-activated, trickling filter, or primary sludges as well as mixtures of the same.