Biogas Digestate – BROWN GOLD
T
he properties and constituents of biogas plants digestate is determined essentially by the materials used as the substrates for the biogas digestion as well as by the digestion process itself. Treatment of animal manure and slurries within the biogas digester results in biodegradation of organic matter to inorganic compounds and biogas. In practice, the anaerobic degradation rate of organic matter from animal manure and slurries is about 40% - 50% for cattle slurry and of 65% - 70% for other animal manures. The degradation rate depends at large on feedstock type, HRT and process temperature. Due to degradation of organic matter, digestate is easier to pump and easier to apply as organic fertiliser, with reduced need of stirring, compared to untreated slurry.
Digestate Characteristics: As mentioned above the physio-chemical characteristics of digestate vary, strongly depending www.biogas-india.com
on the nature and composition of the feedstock used (it may also vary when the same feedstock is used and the characteristics are checked in different plants) as well as on the operational parameters of the biogas process. Researches done till date on digestates from biogas plants indicate that, when compared with raw animal manures and slurries, digestate generally has lower total solids (TS) and total organic carbon (C) content, lower carbon to nitrogen ratio (C:N), and lower viscosity. On the other hand, the pH value and the share of ammonium (NH4+) are higher in digestate compared to raw animal manures and slurries. Some characteristics relevant for the fertiliser quality of digestate can also be studied and discussed. In all most all the developing countries, the traditional substrates are agricultural/ livestock by-products (manure and slurries), biogenBiogas Magazine | Edition 12 | 34
