Optimization of high temperature-pressure pre-treatment process for the enhancement of methane production from Cyanobacteria

In this master thesis, it was aimed to produce methane from cyanobacteria isolated from the water sources of our country which has energy production potential, to apply high temperature-pressure pretreatment process to increase its methane production efficiency and to make process optimization of the pretreatment process. In this context, firstly Desertifilum tharense cyanobacteria were produced, culture specific parameters were determined, characterization analyses were performed, Desertifilum tharense cyanobacterium was subjected to high temperature-pressure pretreatment process in order to increase methane production efficiency and the pretreatment process was optimized for methane production. Dry weight, specific growth rate, maximum productivity and CO2 fixation values of Desertifilum tharense were determined as 3.61 g/L, 0.36 1/day, 0.35 g/L.day and 0.06 g/day, respectively. Desertifilum tharense had a carbon (C) content of 50.2% and total organic carbon content (TOC) of 48.9%. These findings indicate that Desertifilum tharense carbon content is derived from organic carbon and can be used as a biomass source in biofuel production. The BMP of raw Desertifilum tharense sample was measured as 261.8 mLCH4/gVS. In order to investigate the effects of high temperature-pressure pretreatment process and to determine the optimum process conditions, Response Surface Methodology (RSM) Central Composite Design (CCD) was used. Increasing the reaction temperature in high temperature-pressure pretreatment process increased the amount of dissolved chemical oxygen demand (sCOD) and the amount of extractable matter and lipids, while the amount of biochemical methane potential (BMP) decreased. BMP values of the samples treated with high temperature-pressure were measured in the range of 201.5 – 235 mLCH4/gVS and lower than the raw sample. These results revealed that the high temperature-pressure pretreatment process is not suitable for the production of biofuel methane from Desertifilum tharense. Optimization of the high temperature-pressure pretreatment process (optimum process conditions) was carried out in terms of maximum methane production and cost with the help of Design Expert software optimization module and the obtained optimization conditions and results were compared with validation experiments. 200°C reaction temperature and 20 min. reaction time conditions were proposed as optimum for maximum BMP production. With the proposed model, it was estimated that 227.1 mLCH4/gVS methane could be produced under these conditions and 211.4 mLCH4/gVS methane was produced in the validation experiment. As a result of the master thesis, it was determined that Desertifilum tharense cyanobacterium can be used as a suitable biomass source for methane production. However, it was not necessary to use high temperature-pressure pretreatment process prior to the methane production.