Application of anaerobic digestion process for different sectoral wastes

The aim of the thesis study is to eliminate the limited number of disadvantages of the anaerobic digestion process by implementing combined processes and innovative technologies to anaerobic digestion. In this context, three different studies have been carried out to improve anaerobic digestion process performance for different substrates. The purpose of the first study is to enhance the methane production of lignocellulosic waste, which has low methane production potential in anaerobic digestion due to low hydrolysis efficiency, by the application of the pretreatment process. In this context, thermal alkaline H2O2 pretreatment was applied to the banana harvesting wastes formed during the harvesting period of the banana fruit, which is produced intensively in the Antalya region, and the process optimization of the pretreatment process was carried out to enhance the methane production potential. As a result of the optimization procedure of the thermal alkaline H2O2 pretreatment process; the reaction time of 6 hours, H2O2 concentration of 2.73% and reaction temperature of 50°C were determined as optimum pretreatment conditions. Methane production efficiency of banana harvesting wastes treated under optimum pretreatment conditions increased by 40% compared to raw banana harvesting wastes. The methane production model for the optimized pretreatment process conditions predicted a 43.2% increase in methane production compared to the raw sample. It has been determined that the thermal alkaline H2O2 pretreatment process is effective in changing the bond structure and surface properties of banana harvesting wastes. Thermal alkaline H2O2 pretreatment process combined with the anaerobic digestion is an effective pretreatment method for the production of renewable energy from banana harvesting wastes. The purpose of the second study is to overcome the low methane production potential due to nutrient deficiency and unbalanced nutrient content, which caused by the nutrient composition of different organic wastes, by the anaerobic digestion process. In this context, the anaerobic co-digestion performance of vinasse, pomace, and aniseed, which are the wastes of the alcoholic beverage production facility operating in the Antalya region, was investigated. Characterization analysis of vinasse, pomace and aniseed were performed, and anaerobic co-digestion performance was examined at different substrate ratios. The roles of substrates in anaerobic digestion were evaluated together with the concept of waste management. As a result of the study, the mixture of 70% vinasse and 30% pomace showed the highest synergistic effect with the calculated value of α=1.09 for the production of methane by anaerobic digestion. Experimental methane production potentials of wastes were modeled by Modified Gompertz model, Cone model, Reaction Curve model, and First Order Kinetic model to determine the kinetic coefficients of the wastes in the anaerobic digestion process. Experimental methane production results have been successfully modeled by kinetic models with high determination coefficients (R2=0.91-0.99). As a result of the modeling, reaction rate constant (k), lag phase (λ) and maximum methane production rate (Rm) were calculated as 0.253-0.371 days-1, 0.009-0.014 days, and 37.4-48 mL CH4/gVSadded, respectively for anaerobic digestion of 70% vinasse and 30% pomace mixture. It is concluded that an anaerobic co-digestion process is an appropriate approach for the evaluation of alcoholic beverage production wastes. The purpose of the third study is to overcome the low methane production and low biomass growth problems observed in the treatment of diluted wastewaters in anaerobic digestion by the application of membrane processes. In this context, the treatment performance of domestic wastewater in a continuous AnMBR system was examined. As a result of the study, average COD removal efficiencies were obtained as 94.3% and 93.2% for 23 hours hydraulic retention time with 3 LMH flux, and 12 hours hydraulic retention time with 5.7 LMH flux, respectively. The average methane production potential was measured 200 mL CH4/gKOI for the whole operation period. Transmembrane pressure values measured during the operating period of 121 days ranged between 10 mbar and 30 mbar, and no value observed that causes problems in terms of fouling. The outputs obtained within the scope of the doctoral thesis study show that the anaerobic digestion process has a potential to be applied in Antalya scale with appropriate solutions. The doctoral thesis provides a guidance and comprehensive understanding for elimination of disadvantages of the anaerobic digestion processes.