Investigation of biogas performance of mixing biodiesel waste product (raw glycerine) into animal manure in laboratory scale anaerobic reactors

This dissertation includes research on increasing biogas and methane production yield by co-digestion of raw glycerine, which is the main by-product of biodiesel industry, with animal manure by anaerobic fermentation. Due to the widespread use of cattle manure in conventional biogas production, it has been selected as a base of feed and used as waste vegetable oil-derived glycerin as a co-ferment. Within the scope of the thesis, the study has been carried out in two main sections. In the first part, batch feed anaerobic reactor experiments were carried out in order to determine the operating conditions of the use of crude glycerine as an co-ferment in conventional biogas production process. Variance analysis (ANOVA) statistics, response surface methodology (RSM), significance of effects of variables on results and optimum conditions for target values were determined. In anaerobic fermentation process, glycerin / fertilizer ratio is considered as the most important limiting factor for production parameters and methane production. Glycerin / fertilizer ratio, temperature and incubation time values were calculated as 4.5% (v/v), 34oC and 18 days for optimum biogas and methane values when the targets have selected as high biogas yield, high glycerine amount, low temperature and incubation time. In the second part, the effect of optimum operating conditions on biogas and methane gas yield at different organic load values (OLR) in continuous stirred tank reactor (CSTR) was investigated. The addition of 2% glycerin (OLR 1.5 gVFA/L.day) resulted in a 11% increase in methane yield, 104% in biogas and 128% in methane production compared to the control group (OLR 2.2 gVFA/L.day). If this parameter exceeds 6% by volume, it has a negative effect on the stability of the system. When the amount of glycerin is 10%, the system stability and performance is considerably reduced. Methanogenic bacteria were inhibited at a daily glycerin concentration of 2.6 g/L.day (OLR 2.9 gVFA/L.day) and the system failed. Keywords: Anaerobic fermentation, Biogas, Co-fermentation, Glycerin, Optimization, Waste vegetable oil