Effect of Animal Fat on Anaerobic Co-Digestion and Process Optimization

Abstract

One of the emergent challenges in meat processing industries is producing biogas with animal waste associated with high-fat content. This research attempts to find out the effect of animal fat (poultry) on anaerobic co-digestion and process optimization by means of food waste as the co-substrate and cow dung (CD) as the inoculum by considering the trend in biomethane production at different quantities of animal fat. A series of batch fermentations were carried out in a lab-scale batch reactor (>500mL) based on the VDI 4630 protocol. One control batch experiment was conducted with inoculum alone and five other dif ferent co-digestion experiments were implemented in triplicates with the proportions of rendered chicken fat emulsion:food waste at 0:100, 25:75, 50:50, 75:25, and 100:0 (w/w) in the presence of inoculum. The propor tion of substrates to inoculum was 100:300 (w/w) in all the co-digestion experiments. Each experiment was implemented for four (4) days continuously under mesophilic (35°C) conditions and at 200rpm mixing speed by ensuring continuous mixing. Experimental data proved that the highest total biogas potential is achiev able with co-digestion experiments incorporated with high quantities of food waste (0:100, 25:75), though a sudden process failure of acidification occurred eventually, along with minimal organic material conversion rate (mL/gCODremoval). Experiments utilizing relatively high quantities of fat emulsion showed relatively low total biogas production without any sudden process failure and with a high organic material conver sion rate. The highest pH reduction with high COD and volatile solid removal efficiencies were represented by high-quantity food waste incorporated batch experiments. The most viable co-digestion proportion was 50:50 (w/w) among the batch experiments incorporated by food waste with regard to the limited pH drop of the feedstock mixture. Another satisfactory fermentation was the co-digestion of animal fat associated with inoculum (cow dung) without using food waste (100:0), which produced continuous biomethane production with a high rate of organic material conversion. Continuous mixing and stable temperature at 35°C may optimize gas production efficiency, and pH adjustment will be a further optimization technique for achieving the highest possible biomethane production.