Bacteria anaerobic digestion

Except in case of the anaerobic digestion of poultry waste, methane production decreases as retention time is reduced. This is a result of the substrate being exposed for less time to the action of anaerobic bacteria. With the poultry waste, it was noted that methane production increased as the retention time was reduced. Also the methane production in the three retention times studies was much higher than that reached in the mixed wastes study when the retention time was greater than 30 days. 

The acid-forming and methane-forming bacteria work simultaneously in the anaerobic digestion process. Oxygen is excluded from the digester and various other environmental conditions are controlled so that the methane-formers are maintained in balance with the acid-formers. Otherwise, the methane-formers would be inhibited and in some cases would cease to function entirely. 

Biogas or synthetic natural gas production can be accomplished by utilizing the process of anaerobic digestion to convert biomass into methane. This multistage process of anaerobic decomposition involves hydrolysis of complex organic compounds by multiple bacterial species. The bacteria are grouped into the following classes ... 

Lactose is readily fermented by lactic acid bacteria, especially Lactococcus spp. and Lactobacillus spp., to lactic acid, and by some species of yeast, e.g. Kluyveromyces spp., to ethanol (Figure 2.27). Lactic acid may be used as a food acidulant, as a component in the manufacture of plastics, or converted to ammonium lactate as a source of nitrogen for animal nutrition. It can be converted to propionic acid, which has many food applications, by Propionibacterium spp. Potable ethanol is being produced commercially from lactose in whey or UF permeate. The ethanol may also be used for industrial purposes or as a fuel but is probably not cost-competitive with ethanol produced by fermentation of sucrose or chemically. The ethanol may also be oxidized to acetic acid. The mother liquor remaining from the production of lactic acid or ethanol may be subjected to anaerobic digestion with the production of methane (CH4) for use as a fuel several such plants are in commercial use. 

Borja and Banks studied the kinetics of the anaerobic digestion of fruit processing wastewater (COD = 5.1 g/l). They used several substrata as scaffolds for the development of degrading colonies of bacteria. The kinetics of degradation were compared with the kinetics of a suspended biomass. The first order rate constant was determined and is shown in Figure 5.13. While the rate for the polyurethane was lower than rates for the sepiolite and saponite, some of the improvements we suggested and an improvement in mass transport could improve the rates of reaction. In any case, the paper of Borja and Banks suggests effect on kinetics exerted by the substratum. 

There are three major groups of bacteria that function in anaerobic digestion. The first group hydrolyzes large soluble and nonsoluble organic compounds such as proteins, fats and oils (grease), and carbohydrates, producing smaller water-soluble compounds. These are... 

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