Oil in food waste to methane by anaerobic digestion: Co-effects of mixing intensity and long chain fatty acid loading

Oil in the food waste can contribute improved energy yield by anaerobic digestion, and also poses an inhibition risk from the intermediate long chain fatty acids (LCFAs). The digestion performance partly depends on the solubility of oil/LCFAs concerned recently, while mixing intensity control can disturb the solubility characteristics. Combined with oil loading such a fundamental control parameter, co-effects of mixing intensity and oil loading on methanogenic characteristics were illuminated. A series of mixing intensities 0-240 rpm and oil/ inoculum (F/I) ratios 0.2-1.2 were set to conduct a batch experiment, and relevant affecting mechanisms were further disclosed as well. It turned out that variation of mixing intensity could have effects on methanogenesis from oil in food waste. Increasing mixing intensity prolonged lag phase. Mixing intensity at 120 rpm was proved as a starting point to disturb LCFA inhibition. Methanogenic rates climbed to the top at F/I 0.4, and further increase loading resulted in the rate decline. Methanogenic potential release was also reduced with both mixing intensity and loading at higher values. Hereinto, oleic acid (C18:1) as a key LCFA in oil played an important role in inhibition, while higher mixing intensity and loading could promote degradation and conversion of another critical LCFA palmitic acid (C16:0). The study favors achieving a cost-effective strategy controlled by mixing intensity to promote safe energy improvement.