Effects of the addition of waste cooking oil on heavy crude oil biodegradation and microbial enhanced oil recovery using Pseudomonas sp. SWP-4

The present work aims to investigate the effects of the addition of waste cooking oil (WCO) on heavy crude oil biodegradation and microbial enhanced oil recovery (MEOR) using Pseudomonas sp. SWP-4. Growth kinetics show Pseudomonas sp. SWP-4 had a maximum dry cell weight of 1.73 g/L and cell-surface hydrophobicity of 62.4% against n-hexadecane when degraded the crude oil with the addition of WCO. The maximum rhamnolipid concentration was 6.87 g/L, and the culture broth exhibited a higher emulsification efficiency of 58.3% on n-hexadecane and reduced the surface tension of broth to 22.7 mN/m. Meanwhile, Pseudomonas sp. SWP-4 reduced the viscosity of crude oil from 26,300 mPa·s to 550 mPa·s (40°C) and successfully degraded most of the n-alkanes. Furthermore, the fluidity of oil had been well improved after degradation. It can be concluded that not only could WCO stimulate the bacterial growth, but also it could enhance the crude oil degradation. Core displacement experiment demonstrates the efficiency of water flooding was just 5.8%, but the microbial flooding produced by Pseudomonas sp. SWP-4 with the addition of WCO effectively improved the oil recovery further with an additional oil recovery efficiency of 24.4%.