Anaerobic digestion is widely used as a source of renewable energy. The process produces a biogas, consisting of methane, carbon dioxide and traces of other ‘contaminant’ gases. This biogas can be used directly as fuel, in combined heat and power gas engines, or upgraded to natural gas-quality biomethane. The nutrient-rich digestate that is also produced can be used as fertilizer.
USA Tank offers a bolted tank system consisting of epoxy coated carbon steel in the liquid phase and 316 stainless steel in the gaseous phase. This combination allows the minimum use of the corrosion resistant stainless and the more affordable epoxy coated carbon steel in the less corrosive liquid phase. USA Tank also manufactures a vertical panel tank insulation, which is needed to maintain the proper temperature for maximum efficiency of the process.
The process of anaerobic digestion consists of three steps:
- The first step is the decomposition (hydrolysis) of plant or animal matter. This step breaks down the organic material to usable-sized molecules such as sugar.
- The second step is the conversion of decomposed matter to organic acids.
- The last part of the process occurs when acids are converted to methane gas.
Process temperature affects the rate of digestion and should be maintained in the mesophillic range (95 to 105 degrees Fahrenheit) with an optimum of 100 degrees F. It is possible to operate in the thermophillic range (135 to 145 degrees F), but the digestion process is subject to upset if not closely monitored.
Many anaerobic digestion technologies are commercially available and have been demonstrated for use with agricultural wastes and for treating municipal and industrial wastewater.