Study On Treatment Of High-strength Oil-containing Wastewater By Mixed Yeast

The BOD5/COD ratio of the salad oil-containing wastewater is higher than 0.3 which indicates that the wastewater can be treated by some biochemical methods. However, high content of oil in the wastewater make it impossible to treat the wastewater efficiently by using conventional aerobic or anaerobic activated sludge. The sequencing batch reactor (SBR) is a new compact, efficient and easily-operated wastewater treatment technique and was reported that it could be operated at higher BOD load with good sludge settleability.Yeasts have a good flocculation capability and can endure low pH or high osmotic pressure environments, which make yeasts superior to treat high-strength organic wastewater. By comparison with the conventional activated sludge, the yeast-SBR technique consumes less oxygen and produces less excess sludge and can endure high BOD load. The excess yeast contains much quantity of protein and many kinds of amino acid, which can be used as a kind of single cell protein (SCP). Therefore, the yeast-SBR technique is characterized by high efficiency and low cost. In this paper, yeasts were applied to SBR to treat high-strength oil-containing wastewater. The morphology of yeasts was followed and the operation parameters were optimized too.The quality of wastewater was analyzed which indicates that this kind of wastewater contains high content of oil and COD. The BOD₅/COD_cr ratio was more than 0.3 and the wastewater could be treated by biochemical method. However, this wastewater was short of nitrogen and it was necessary to supply nitrogen source to the wastewater when it was treated. At the other side, the pH of this wastewater was very high and pretreatment was needed before biochemical treatments.Oil degradation experiments demonstrated that the strains, G1, W1 and 02 could degrade oil obviously. The strains, W1, W2, Gl and G2 were observed to form filament morphology when they were cultivated in wastewater medium. Therefore, it was possible that these strains could induce the filamentous bulking.The operation parameters were optimized by a series of experiments and showed that the optimized pH, HRT and BOD load was 5, 9 hr and 1.5 kg BOD/(kg MLSS d), respectively.The stability of yeast-SBR system was investigated and showed that temporary pHchange made a little effect to the system and the effect was reversible. The 100-day continuous experiments indicated that the system could be operated under pH5 with high removal efficiency and good sludge properties. The removal rate of COD and oil achieved 90% and 95%, respectively. The effluent can be treated by conventional activated sludge and meet the discharge standard.