Investigation of methaneproducti̇on from switchgrass to increase the amount of methane by co-fermentation

Fossil resources, which are depleted day by day, lead researchers and energy producers to new energy sources. At the same time, the use of fossil fuels for many countries brings them significant disadvantages such as external dependence, import costs and environmental problems. As a result of these developments, the importance of renewable energy sources is increasing and developed countries are devoting great resources to R & D studies in this regard. As is known, in terms of Turkey is largely dependent on foreign sources of energy. 75% of the energy consumed is imported (DB, 2016). Therefore, high energy crops, as energy sources, have started to increase in our country as well as all over the World. The studies to be carried out on switchgrass plants, is one of the solutions to the problem of energy supply which is the most important foreign exchange expense of our country, and it is important to provide alternative feed source opportunities in terms of animal husbandry in addition to energy of the same product. Within the scope of this doctoral thesis, it is aimed to optimize the pre-treatment of thermo-chemical (Calcium hydroxide- Ca(OH)2) (lime) process to increase the amount of biochemical methane potential that can be produced from switchgrass plant. For this purpose, thermo-chemical Ca(OH)2 pretreatment assays were performed with the Response Surface Method (RSM) used for the analysis, modeling and optimization of engineering problems. Biochemical methane potential (BMP) test results were used as response variables in the optimization of the pretreatment process planned with RSM. Thermo-chemical Ca(OH)2 pretreatment process was modeled using the response variable values, optimum process conditions were determined for maximum biochemical methane potential and validation test was performed to determine the accuracy of process optimization conditions. In order to determine the effect of thermal- Ca(OH)2 pretreatment applied to branched Shawnee varieties on methane production, 56-day BMP test was performed by using thermal- Ca(OH)2 pretreated samples. The highest amount of methane obtained as a result of BMP tests was at 100 °C reaction temperature, 16 hours reaction time, 0% Ca(OH)2 concentration and 3% SM amount as 231.41 mLCH4/gVS. As a result of BMP test with crude switchgrass without pretreatment, this value was obtained as 217.1 mL CH4/gVS. After pretreatment BMP increasement was calculated as 6.2% compared to raw switchgrass. In the modeling process performed with the help of Design Expert program, the value of R2 for BMP was calculated as 0,8572. Optimal pre-treatment conditions were preferred to produce maximum methane in the optimization of pretreatment. These conditions were determined to be 6 hours reaction time, 3% solid matter, 0% Ca(OH)2 concentration and 100 °C reaction temperature. The validation test of these conditions was found as 248.77 mLCH4/gVS with an error of 16.51%. In the second optimization, the maximum amount of methane produced by minimizing the inputs and the most suitable pre-treatment conditions were determined. These conditions were found to be 6 hours reaction time, 3% solid matter, 0% Ca(OH)2 concentration and 53.5 °C reaction temperature. As a result of the validation test, the amount of methane produced with an error of 5.52% was found as 220.5 mL CH4/gVS. Although the percentage of error measured for BMP is higher than the percentage of optimization, it is considered that the this ratio is acceptable and the model is usable. Buswell equation was used to find the amount of theoretical methane that could be produced by co-fermentation of switchgrass and chicken manure. Seven mixing ratios were determined in the co-fermentation of switchgrass and chicken manure. According to the results of the elemental analysis, theoretical BMP values were determined by considering these mixing ratios. The highest theoretical BMP value (437 mLCH4/gVS) was reached in the mixture without chicken manure. Thermo-chemical Ca(OH)2 pretreatment and anaerobic digestion processes applied to energy plant switchgrass were aimed to enrich the methane production. In this study, optimum pre-treatment process conditions were determined. In addition, increasing the amount of biochemical methane production by co-fermentation of energy plant and poultry manure, producing energy by evaluating waste and examining the co-fermentation process of both wastes have contributed to the literature.