Enzymatic hydrolysis of floatable fatty wastes from dairy and meat food-processing industries and further anaerobic digestion

The wastewater from food-processing industries is generally heavily charged with lipids and proteins. Flotation process is commonly applied to separate the hydrophobic material phase, producing flotation froth, a waste that has high levels of fats and proteins. Enzymatic hydrolysis may be used to overcome the difficulty of fat biotransformation in a subsequent anaerobic digestion. In the present work, wastes from the flotation process of two industries (dairy and poultry slaughterhouse) were hydrolyzed with a commercial lipase and without enzyme addition (control). The effect of adjusting the pH at the beginning of the hydrolytic assays was also investigated. The long chain free fatty acids (LCFAs) released were identified and quantified and 5-d digestion assays were conducted with the hydrolyzed material. The results indicated that the hydrolysis assays conducted with initial pH adjusted to 7.0 and the utilization of a commercial enzyme promoted a higher increase in amounts of LCFAs, particularly of unsaturated acids. In most anaerobic digestion assays, the specific methane production showed a decreasing trend with the increase of unsaturated fatty acids in the medium. In general, the utilization of a commercial enzyme (lipase) in the hydrolysis process did not contribute to enhancing methane production in 5-d anaerobic digestion assays.