Anaerobic digester

The performance of anaerobic digestion processes varies according to the type of unit, throughput, and feed concentration, but such processes are typically capable of removing between 75 and 85 percent of COD. ... 

In attached growth film) methods, as with aerobic digestion, the microorganisms can be encouraged to grow attached to a support medium such as plastic packing or sand. In anaerobic digestion, the bed is usually fluidized rather than a fixed-bed... 

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Ana.eroblc Digestion. Methane can be produced from water slurries of biomass by anaerobic digestion in the presence of mixed populations of anaerobes. This process has been used for many years to stabilize municipal sewage sludges for purposes of disposal. Presuming the biomass is all cellulose, the chemistry can be represented in simplified form as follows ... 

Fig. 4. Microbial phases in anaerobic digestion A, hydrolysis B, acidification C, methane fermentation.

Gasification. Conversion of biomass to gaseous fuels can be accompHshed by several methods only two are used by the biomass energy industry (ca 1992). One is thermal gasification in which LHV gas, ie, producer gas, is produced. The other process is anaerobic digestion, which yields an MHVgas. 

Table 37. Potential Methane Production from Commercial U.S. Anaerobic Digestion Systems...

R. L. Wentworth, "Anaerobic Digestion in North America," paper presented at Symposium Anaerobic Digestion and Carbohydrate Hydrolysis of Waste, sponsored by Commission of the European Communities, Luxembourg, May 8—10,1984. 

J. H. Ashworth, Y. M. Bihun, and M. La2ams, Universe of U.S. Commercial-Scale Anaerobic Digesters Results of SERJ/ARD Data Collection, Solar Energy Research Institute, Golden, Colo., May 30,1985 J. H. Ashworth, Problems With Installed Commercial Anaerobic Digesters in the United States Results of Site Visits, Rev. ed.. Solar Energy Research Institute, Golden, Colo., Nov. 6, 1985. 

The microorganisms grow in response to the food source suppHed in the wastewater and produce more biological sludge than is needed to maintain the process. This excess sludge must be wasted from the process and is usually treated by dewatering and aerobic or anaerobic digestion. 

Anaerobic ponds are loaded such that anaerobic conditions prevail throughout the Hquid volume. One of the major problems with anaerobic ponds is the generation of odors. The odor problem can frequentiy be eliminated by the addition of sodium nitrate at a dosage equal to 20% of the appHed oxygen demand. An alternative is the use of a stratified facultative lagoon, in which aerators are suspended 3 meters below the Hquid surface in order to maintain aerobic surface conditions, with anaerobic digestion occurring at the lower depths. 

Sludge Stabilization. Organic sludges need to be stabilized before ultimate disposal except in the case of incineration. This is usually achieved by either aerobic or anaerobic digestion. In aerobic digestion, the degradable volatile soHds are Hquefted and oxidized to CO2 and H2O. In anaerobic digestion the soHds are Hquefted and fermented to CH and CO2. 

Fig. 3. Process components for the activated-sludge process, with aerobic digestion at plants <473.1 m /h and two-stage anaerobic digestion at plants...

Sludge is destroyed by microorganisms and the kinetics of their life processes is temperature dependent. Short anaerobic digestion detention times are obtained at 35°C. Even shorter detention times are possible at 52—54°C, but detention in this range is costly. An increase in detention time occurs at 35—43°C and then a progressive decrease takes place until 52—54°C. This variation is caused by a change in character of the dominant process organisms. 

Stabilization (Anaerobic Digestion, Aerobic Digestion, High Lime... 

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