Pseudomonas aeruginosa STQ-2 and rhamnolipid synergistically enhance the removal rates of oil and chemical oxygen demand (COD)
image: Figure Oil degradation rate in kitchen leachate at different fermentation times. A: Concentration of leachate containing 5.0 g/L WCO; B: Concentration of leachate containing 20.0 g/L WCO.
Credit: Microbiology China
Food waste leachate contains high levels of oil and other organic matter, making it difficult to treat. Because oil disperses poorly in water, microorganisms may have limited access to it. A team from Zhejiang A&F University—Zheng Mengqiu, Shi Tianqing, Zhang Yanfen and Zheng Huabao—investigated whether combining an oil-degrading bacterium with a biosurfactant could improve treatment.
The researchers paired Pseudomonas aeruginosa STQ-2, a strain isolated from food waste leachate, with fermentation supernatant containing rhamnolipids. They compared this combination with the strain alone, the supernatant alone and a blank control. Rhamnolipids help disperse oil in water, making it more accessible to microorganisms.
At an initial used cooking oil concentration of 5.0 g/L, the combined treatment achieved approximately 89.9% oil degradation and 95.6% chemical oxygen demand (COD) removal after 96 hours, outperforming the other groups. COD is a common measure of organic pollution in water. At a higher initial oil concentration of 20.0 g/L, the corresponding rates were approximately 69.4% and 36.1%, showing that performance varied with oil concentration.
The researchers also observed changes in the leachate’s microbial community during treatment. The authors concluded that STQ-2 and rhamnolipids worked together to improve oil degradation and COD removal. The findings provide a basis for further research into biological treatment of oily food waste leachate. Further studies would need to test performance across leachate sources and assess the conditions for larger-scale use and the safety of applying the strain.