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

• Published in: Energy conversion and management 2013-07, Vol.71, p.92-100
• Main Authors: Yangin-Gomec, Cigdem, Ozturk, Izzet
• Format: Article
• Language: English
• Subjects: Ammonia inhibition; Applied sciences; Biogas production; Biomass; Co-digestion; Energy; Energy savings; Exact sciences and technology; Maize silage; Manure; Natural energy; Zea mays
• ISSN: 0196-8904; 1879-2227
• DOI: 10.1016/j.enconman.2013.03.020

•Daily biomethane and total energy productions improved 1.2 fold when maize silage is co-digested with the animal wastes.•Heat produced is sufficient for successful mesophilic co-digestion with an energy saving ∼36×103kWh with maize silage.•Excess heat up to 16×103kWh can be utilized elsewhere in the premises of the biogas plant.•Biogas plants including co-digestion of manure with a suitable co-substrate are becoming net producers of renewable energy.•pH values above 7.4 may cause severe inhibition of methanogenic cultures for an unadapted process to NH3. The aim of this study is to evaluate the biogas recovery potential if mesophilic (35±2°C) 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 6580m3/day corresponding to total energy productions of some 45.05×103 and 51.06×103kWh 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°C). 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 especi