Biogas from Animal Manure – Perspectives and Barriers in Bulgaria

This paper aims to review the perspectives and barriers before production of biogas from animal manure in Bulgaria.
The share of methane emissions from the agricultural sector in Bulgaria occupies 18 % and stored animal manure is its biggest source. The use of animal manure for production of biogas could reduce these emissions. Biogas market in Bulgaria is not well developed yet, but the potential of biomass for biogas production is promising. Residues and waste from animal production as well as crop residues are important renewable energy sources for Bulgaria as raw materials for biogas production. Animal manure availability from cattle- and pig- and poultry farms in Bulgaria are presented. The content of N, P and K in the manure is discussed in view of further use of the residues of biogas production as soil nutrients. Advantages and barriers to biogas production in Bulgaria are discussed.
Presented data reveal a promising resource for biogas production by anaerobic digestion. The total energy of methane from pig manure is estimated to the value 6703 PJ. Additionally about 25188 PJ from cattle manure are available, and from poultry roughly other 3684 PJ.
The comparison of needs of N, P and K for soil fertilization with the quantities of these elements, available from animal manure allows concluding that the biomass residues from biogas production could play considerable role in soil fertilization.
To fasten and enlarge the introduction of anaerobic digestion of manure it is necessary to formulate as mandatory requirement in applying for subsidy: every farmer should build concrete platforms for storage of fresh manure (from pigs) and lagoons (though open). It assures also the ecological advantage to prevent nitrogen contamination of soil, and groundwater.