The biodegradation of olive oil and the treatment of lipid-rich wool scouring wastewater under aerobic thermophilic conditions

The biodegradation of olive oil and the treatment of the lipid-rich wool scouring wastewater were studied under aerobic thermophilic (65°C) conditions using the newly isolated strain Bacillus thermoleovorans IHI-91. In a continuously operated laboratory-scale stirred-tank reactor olive oil was degraded to more than 90% at a residence time of 2 h with a maximum volumetric degradation rate of 900 mg l−1 h−1. A relatively high maximum biomass yield of 1.05 g dry cell weight per g olive oil consumed was measured and a maintenance coefficient of 0.04 g olive oil (g DCW)−1 h−1 was calculated from steady-state data. A severe growth inhibition was observed when the feed olive oil concentration was increased to more than 4 g l−1. Lipid removal from the highly loaded wool scouring wastewater (COD of 77000 mg l−1) was 20–30% at a residence time of 10–20 h while the COD removal was 15–20%. GC-MS analysis revealed that longchain fatty acids up to C18 were efficiently degraded while degradation of the predominant sterol-fraction of the wool grease was not detected. The high concentrations of volatile fatty acids (60 mM acetic acid, 13 mM propionic acid) present in the wastewater were completely removed even at residence times of 2 h. Compared with data from mesophilic processes the lipid degradation rates obtained under thermophilic conditions are extremely high.