Biogas plant, as a rule, consists of gas- and water-tight vessel in which organic waste mass, wastewater, etc is digested under certain temperature with biogas generation.
The operation principle of all biogas plants is the same: after collection and preparation of substrate that consists of bringing it to needed moisture level in special vessel, it is loaded in digester, where special conditions for optimization of digestion process are created.
The process of generating biogas and biofertiliser from substrate is called fermentation, or digestion. Digestion of substrate is made possible due to special bacteria. During the time of digestion on the top of substrate appears scum which should be broken down by agitation. Agitation can be manual or conducted with special equipment inside the digester and assists to free generated biogas from the substrate.
Generated biogas after purification is collected and stored until utilization in gasholder. From the gasholder to the place of biogas utilization in domestic or other gas appliances gas is carried through piping system. Substrate, fermented in digester is transformed into biofertiliser and is unloaded through outlet in digester and applied to land, stored or used as fodder addition for animals.
Optimization of substrate digestion process
Conditions necessary for fermentation of organic waste inside the digester of a biogas plant, apart from anaerobic environment include:
• maintenance of temperature regime;
• availability of nutrients for bacteria;
• correct choice of digestion time and timely load and unload of substrate;
• observance of correct PH ratio;
• observance of appropriate C/N ratio;
• correctly chosen proportion of solids content and proper agitation;
• absence of inhibitors of the digestion process.
Types of biogas plants
There are many designs of biogas plants. They can be distinguished by method of loading the substrate, outside appearance, component parts and materials they are made of.
With regard to substrate load method there are batch and continuous types of plants that differ from each other in fermentation period and regularity of substrate load. The most effective from the point of view of maximization of biogas and fertilizer production are continuous plants.
From outside appearance plants can be distinguished according to method of accumulation and storage of biogas. Biogas can be accumulated in the upper hard part of the digester, under a flexible dome or in a special gasholder, floating or standing apart from the digester.