INFLUENCE OF RATIO BETWEEN INOCULUM AND ORGANIC SUBSTRATE ON THE YIELD OF BIOGAS
Determining a methane potential of organic substrates is an important task at the design stage of biogas complex, plants or stations. The raw substrates differ in their composition throughout the year especially those that contain droppings or manure. Therefore laboratories are usually set up at biogas plants to check the characteristics of the raw substrate and perform test to determine its methane potential. The aim of the work is to research the yield of biogas depending on the ratio between the inoculum and the substrate. The condition under which the value of the ratio between inoculum and substrate can be considered rational is given, namely: it is necessary that the deviation of the value of biogas yield was insignificant relative to small changes in the ratio between inoculum and substrate. The results of experiments on methane anaerobic conversion of cow manure at different values of the ratio between inoculum and cow manure are presented. The yield and composition of biogas and the degree of degradation of volatile solids have been determined. The optimal value of the ratio between the inoculum and the cow manure has been determined. The necessity of substrate mixing during methane potential test in laboratory conditions was analyzed. It has been found that for organic substrates that are easily digested or sufficiently diluted with water, it is sufficient to shake the contents of the reactor manually once a day. If the organic substrate is composed of components that are difficult to digest or the organic substrate contains a high amount of dry matter, mixing is mandatory. The mixing method for the test for methane potential of organic substrates containing cow manure is given. There are two criteria according to which the choice of the ratio between the inoculum and the substrate for different types of organic substrates when determining their methane potential should be performed: the first criterion is the presence of its own cell biomass in the substrate; the second criterion is the presence of mostly easily fermentable components in the substrate. The required values of the ratio between the inoculum and the substrate are recommended for organic substrates that are promising and can be primarily used in biogas plants. Bibl. 20, table 3, fig. 1.
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