Effect of maize silage addition on biomethane recovery from mesophilic co-digestion of chicken and cattle manure to suppress ammonia inhibition

摘要

The aim of this study is to evaluate the biogas recovery potential if mesophilic (35 ± 2 ℃) anaerobic co-digestion of two different types of manure sources (from chicken and cattle) is applied at a biogas plant. In order to evaluate the improvement in biogas production in the presence of the co-substrate, maize silage is digested together with the animal manure. Results indicated that daily biomethane and total energy (power + heat) productions improved about 1.2 fold when maize silage is co-digested with cattle and chicken wastes. The heat and power energy potentials from the produced biogas were determined using the conversion rates of a CHP unit. Significant energy recovery could be achieved for both cases; i.e. total methane productions were calculated as 5800 and 6580 m3/day corresponding to total energy productions of some 45.05 × 10~3 and 51.06 × 10~3 kWh without and with maize silage addition, respectively. A heat analysis was also performed where the resulting biomethane productions were the basis of the heat requirements. Results indicated that the major part of the heating requirements consisted of slurry heating to the operating temperature (in this study 35 ℃). When the overall heat requirements are compared to the heat potential from a CHP unit, it is clear that the heat produced is sufficient for successful mesophilic co-digestion giving energy savings as well as the excess heat can be utilized elsewhere in the premises of the biogas plant. Hence, treatment plants including co-digestion of chicken and cattle manure with a suitable co-substrate are becoming net producers of renewable energy if appropriate energy recovery technology is provided. Although the improvement in biogas and energy savings demonstrated that co-digestion of these two different organic wastes is viable with maize silage as the co-substrate, the co-digester needs control due to possible inhibition by high free ammonia levels especially from the chicken livestock.