Degradation of alkanes Alkanes are the main components of petroleum. In the process of petroleum exploration, extraction, transportation, processing and storage, it is inevitable that petroleum will be discharged into the environment and cause pollution to soil and groundwater. In order to improve the degradation rate of alkanes, the addition of biosurfactants can enhance the hydrophilicity and biodegradability of hydrophobic compounds, increase the number of
microorganisms, and then improve the degradation rate of alkanes.Noordman et al.[12] studied the degradation of cetane by different types of surfactants, and the results showed that the degradation of cetane by the biosurfactant rhamnolipids was significantly better than that by fourteen chemically synthesized surfactants. Rahman et al [13] found that the degradation of hydrocarbons in gasoline contaminated soil was increased by 11.9%-45.2% and 20.2%-48.3% in composting system with 0.1% and 1% rhamnolipids, respectively. Recently, Rahman et al. [14] also found that the addition of rhamnolipids significantly increased the degradation rate of alkanes when they studied the degradation of n-alkanes in a mixed composting process of muddy sediment and soil at the bottom of oil storage tanks.
Promote the degradation of polycyclic aromatic hydrocarbons (PAHs) PAHs have received increasing attention due to their “triple” (carcinogenic, teratogenic, mutagenic) effects, and have been listed as priority pollutants in many countries. It has been shown that microbial degradation is the most important way to remove PAHs from the environment, and the degradation performance of PAHs decreases with the increase of the number of benzene rings, and PAHs below three rings are easy to be degraded, while PAHs above four rings are more difficult to be degraded. So far, there are three hypotheses about the ability of PAH-degrading bacteria to promote the bioavailability of PAHs: (1) Promoting the degradation of PAHs through the secretion of biosurfactants [15]. (2) Degradation of PAHs is promoted through the production of extracellular polymers [16]. (3) Promote the degradation of PAHs by forming biofilms [17,18].The experimental results of Johnsen et al. [19] showed that oligotrophic Sphingomonas sp. promotes the degradation of PAH compounds by secreting the surfactant, glucolipids.
For the removal of toxic heavy metals Because the pollution process of toxic heavy metals in the soil environment is characterized by hiddenness, stability and irreversibility, the remediation of toxic heavy metal pollution in soil has been a hot research topic in the academic world. At present, heavy metals in soil can be removed by vitrification, immobilization/stabilization, heat treatment and other techniques. Vitrification is feasible, but the project is large and expensive; immobilization process is reversible, so it is necessary to continuously monitor the treatment effect after treatment; and heat treatment technology is only suitable for removing volatile heavy metals such as Hg. Therefore, low-cost biological treatment methods are developing rapidly. In recent years, people began to use ecological non-toxic biosurfactants to remediate the soil contaminated with heavy metals.The experimental results of Torrens et al[20] showed that the addition of rhamnolipids increased the removal rate of Cd by 8%~54%.Mulligan et al[21] used 0.25% of salvatrol for 5 d to rinse the soil contaminated with heavy metals and then the removal rate of Cu was up to 70%. Mulligan et al [22] used three different biosurfactants to rinse sediments contaminated with heavy metals Cu and Zn. The three biosurfactants had different effects on the removal of heavy metals: 0.5% rhamnolipid had a better effect on the removal of Cu, with a removal rate of 65%; 4% acacia glycolipid had a better effect on the removal of Zn, with a removal rate of 60%; and salvantine had little effect on both, with a removal rate of only 15% and 6%. The changes of heavy metals in sediments were also studied, in which rhamnolipids and salvatrol mainly removed Cu in organically bound state, and acacia glycolipids mainly removed Zn in both oxide-bound state and carbonate-bound state, and the results of this study also confirmed that it is feasible to remove heavy metals by flushing sediments with biosurfactants.
Prospect Biosurfactants are widely used in petroleum, chemical, pharmaceutical, cosmetic, food and other industries, and thus have a promising market prospect. At present, most of the biosurfactant research is still in the laboratory or simulation stage, the main reason is that the production cost is still very high, and there is no obvious competitive advantage compared with the chemical synthetic surfactants, and the application of pollutants in the treatment of limitations. In order to realize the large-scale industrial production of biosurfactants and improve the practical application, future research will focus on the following three aspects: (1) Selection and breeding of strains with high yield that can use inexpensive carbon as substrate (e.g., Benincasa et al. [23] utilized the waste products from sunflower oil production),
(2) In the application of biosurfactants with high purity requirements, cost-effective product separation and purification methods should be designed. The secondary development of products used in cosmetics, food, pharmaceutical and other industries can offset the high production cost of biosurfactants to a certain extent. (3) Study the mechanism of organic pollutant degradation by biosurfactant-producing bacteria, clarify the role of biosurfactants in the polluted site, so that it can quickly and effectively degrade pollutants when directly applying Translated with DeepL.com (free version)
