Effect of false flax oilcake in thermophilic biogas production

Abstract

False flax oilcake has been found to be suitable for anaerobic fermentation in mixtures with cattle slurry and straw. In organic farms, digestion of cattle dung and wheat straw with 8 % dry matter content mixed with 5 % of total material weight false flax oilcake is a feasible option for utilizing false flax oilcake to produce farm-own renewable energy and offering farm-own high nitrogen (ammonia) content fertilizer (2.48 g kg-1 wet wt). In field digesters, the biogas yield of 8 % dry matter pure material under thermophilic condition was 0.24 l g-1 VS fed. The biogas yield could be increased by mixing 5 % false flax oilcake to get 0.37 l g-1 VS fed and a VS conversion efficiency with 0.83 l g-1 VS destroyed. Under laboratory controlled conditions, the biogas yield of slurry with 0.5 % oilcake was a little higher than biogas yield of the digestion of pure material, which was 0.26 and 0.24 l g-1 VS fed, respectively. Compared with the field experiment, only small amounts of biogas were produced in the lab-scale when 5 % oilcake was mixed in. The mixing can improve the biogas yield and substrate reduction in the digesters which have sufficient material. Further research is needed to find out the best controlled conditions (high-efficient bacteria, mixing frequency and time) and best equipment (for example: two phases digesters)