Applicability of digestates from biogas plant in Korea as a liquid fertilizer

Abstract

Recently, global warning and environmental disaster has triggered reduction of greenhouse gases generated by fossil fuel and development of alternative green energy source worldwide. In this situation, as anaerobic digestion of organic wastes can actively follow global trend and generates sources of green energy, research is being briskly carried out. Unfortunately, organic by-product is produced during anaerobic digestion of organic wastes into biogases, and the disposal of these materials is needed. In biogas plant by-product separates solid and liquid by-product through solid-liquid separation process. Domestically, biogas plants recycles solid by-products as compost, decomposed manure, cover material of landfill and cement material. Most of liquid by-products are not being recycled, except recycling livestock excretion as fuel in biogas plant. This thesis evaluates the possibility of recycling of liquid by-product from anaerobic digestion for liquid fertilizer and analyzed components of by-product sample of biogas plants in Korea. Also, reviewed related law for liquid by-product disposal. Suitability of separated liquid as liquid fertilizer is analyzed by standard of liquid fertilizer following standard of commercial fertilizer, and their components are compared with commercial liquid fertilizer to decide recycling possibility of separated liquid as liquid fertilizer. The contents of heavy metals in all the samples are lower than harmful component contents of standard commercial fertilizer livestock manure fermented solution. The coliform group bacteria are found in all the samples except food waste leachate and co-digestion of livestock manure and food waste sample and their concentration is 20~440 CFU/mL. It is very lower than that of the water quality standard of groundwater and effluent quality standard of water pollutants. No E.coli and salmonella spp. are found in the samples. The separated liquid from other feedstocks (food waste, sewage sludge, co-digestion etc.) except from biogas plant using livestock manure as feedstock (food waste below 30% is acceptable) cant use as liquid fertilizer. Therefore, two solutions were suggested to correct this problem.