Kinetic characterization of saponified domestic lipid residues aerobic biodegradation

As the sanitary landfill dumping of the lipidic residues are now prohibited by French legislation, new treatment ways such as biodegradation or incineration have to be developed. This work carried out on domestic grease demonstrates the effect of their saponification on their aerobic biodegradation. The composition of the lipidic residues mixture used in this work and collected from a wastewater plant was characterized (70% dry matter, 90% HEM, 80% of free and esterified fatty acids, 20% of other lipidic materials, DCO/lipids=2.4). Both the solubilization of grease (apparent CMC=0.7 g HEM/l) and their micellization by saponification highly enhanced the rate of grease degradation by an activated sludge. This pointed out that the elimination reaction was controlled by the grease transfer from lipidic phase to cell. During batch culture (X0=1.8 g MLSS/l, S0=3.5 g HEM/l), the degradation rate was more than 0.2 g HEM/l/h and the removal yield was 60% for HEM, namely 70% for fatty acids and 40% for unsaponifiable compounds. This low removal yield could be linked to the high foaming onset which did not allow the biological degradation reaction to continue.