Effect of pasteurization pre-treatment on biogas production efficiency

The truth of run short fossil fuels that emit greenhouse gases which are continuously decaying from past to present bring along alternative studies by increasing the energy supply to planning, stability and continuity needed for progression and advancement. Energy demand which occurred by increasing of the population and consumption among society, obliged to face renewable energy sources foreign dependent countries like Turkey. Effects of global warming also give acceleration to these alternative studies. It is necessary to carry out research renewable energy project in order to protect from global warming effect. Renewable sources such as solar, wind, geothermal, hydraulic and biomass which cover both demand of energy and sustainable and clean environment are the crucial orientations. Since our country is an agricultural and livestock country biomass energy system comes into prominence in the near future. Progression of production activities with development of industry and technology cause the food requirement in a parallel to increased population. This matter makes food waste topic crucial. Food wastes may be confronted from raw status before the agricultural activities start to be procured to the end user to us. Food wastes which are confronted in these periods, continue their lives as solid wastes. Disposal of solid wastes become crucial due to sustainability. Sanitary landfill sites which host food wastes are the least preferred situation, and to be applied as final disposal methods but sanitary landfills are difficult systems to control due to unpleasant smell, reproductive of insects dangerous to environment and posing a danger of seepage water. The least preferred systems are applied very common and active in our country. The top amount of wastes in these systems bring with energy recover systems. Biomass energy is still being supported by Renewable Energy Resources Support Mechanism (YEKDEM) under guarantee as 0,133 USD/kWh in a ten year limitation period. This incentive amounts can be increased by using local materials and equipment in conversion technologies. Biomass energy contain agricultural wastes, animal wastes, forest wastes, crops apart from food wastes. Different types of wastes are evaluated in different forms of conversion technologies. For power generation thermochemical and biochemical methods are used. These methods are combustion, pyrolysis, gasification, anaerobic digestion and landfill gas which are obtained from sanitary landfill sites. Anaerobic digestion is the most efficient system among the others as already evaluated in this study, is confronted as the most suitable technology for food wastes. Through this method, containing top amount of methane and carbon dioxide biogas is obtained. Obtained biogas is converted to the electrical energy by using gas engines. Also it is possible to recover waste heat to use for process. After process, high quality compost is derived except biogas. Before electrical energy conversion, pasteurization process is applied to the obtained biogas to purify from possible pathogens inside the food wastes. This process is compulsory in European Union and Turkey regulations and legislations. In this process feeding is waited in 1 hour period under 70 oC. In our study this compulsory application was examined if the purifying from pathogens will be sufficient. After this process, measurement of bacteria was observed and continued to measurements again. Generalization of solubility is increasing directly proportional was observed in different thermal process periods. At the same time application of this compulsory of the regulation and to be applied and not to be applied, compared to the effect for the obtained biogas from anaerobic fermentation. As a result of these observations, the best two solubility values of process periods feed to the digester and the amount of the biogas was compared as well. The food wastes which comparisons made were taken from Istanbul Technical University central campus cafeterias. The food wastes which occurred in campus cafeteria were brought to the Istanbul Technical University Solid Waste Laboratories and conserved under 4 oC. Approximately 50 kg amount of food wasted were turned into small pieces by using 550 Watts chopper. Small pieces of food wastes contain Total Solid (TS), Total Volatile Solid (VS) , Total Kjedhal Nitrogen (TKN), Total Phosphor (TP) and pH analysis. Thermal process was made by taking base of 70 oC in 1 hour period, was waited under 70 oC in 15 minutes, 30 minutes, 1 hour, 2 hours, 3 hours, 4 hours, 6 hours, 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours, 24 hours, 27 hours, 30 hours, 33 hours and 36 hours. In these methods solubility of pretreatment, pH and variability of conductivities were examined in different time periods of application. It is observed that the solubility increased when the time period exposed under heat increases. The optimum time periods are 30 hours and 36 hours period were observed among the all pretreatment process periods. In these time periods COD (Chemical Oxygen Demand) is measured as 47.888 mg/L. The conductivity which is directly proportional to solubility also increased dependent on the time periods. pH decreased while the heat period increased. In addition to this study, the temperature of the fermenter feeding without pretreatment is observed the dissolved COD values during 6 hours, 12 hours, 18 hours, 24 hours, 30 hours and 36 hours time periods. Without the pretreatment, the best solubility value is 36.736 mg/L under mesophilic conditions at 36 hours period. This value increases 41.656 mg/L under thermophilic conditions at 36 hours period. Also, during the pretreatment in all time periods, total coliform, Escherichia coli and fecal coliform bacteria amount is observed. In our thesis study, it is examined that if the removal of the pathogens is sufficient in this mandatory application. The measurement of bacteria after this process was observed in a different feeding time periods and the measurement was repeated. After all experiments and examinations, it is seen that 1 hour pretreatment application is sufficient for the removal for Escherichia coli and fecal coliform bacteria. However, this pretreatment is insufficient for the removal of total coliform bacteria. After the results of the thesis study, research studies will be continued. According to the result values of solubility, the pretreatment temperature will be specified for digesters. For the first digester, 24 hours period is specified for the solubility values which is the closest to the maximum value. For the second digester, the pretreatment period was shorten to 8 hours period. Then it is decided that 1 hour period pretreatment will be made for the third digester and there will not be any pretreatment for the fourth digester. In mesophilic conditions, the feeding will be feed daily. The obtained biogas yields comparison will be made between the digesters which have different conditions. After biogas yield will be defined, the content of biogas will be examined as carbon dioxide, methane, etc. Then methane values will be compared which is the most important component of biogas.