Results revealed that extracted biosurfactant removes not only the leachable or available fraction of heavy metals but also the bound metals as compared to tap water, which removed the mobile fraction of the metal ions only. Contaminated soil washing with tap water shows only 2.75% of Cd and 9.8% of Pb removal whereas washing with rhamnolipids removed 92% of Cd and 88% of Pb after 36 hours of leaching.
A study of Diaz et al. [71] on biosurfactants application shows their ability to change the surface of many metal ions and their aggregation on interfaces favoring the metal separation from contaminated environments. The authors evaluated the metal removal efficiency of rhamnolipids and bioleaching with a mixed bacterial culture of Acidithiobacillus thiooxidans and Acidithiobacillus ferrooxidans from mineral waste/contaminated soils using alternate cycles of treatment. Results reflect that bioleaching alone is effective in Zn removal with a value of 50% but for Fe it was not very effective and removed only 19%. When rhamnolipids were used at low concentration (0.4 mg/ml), 11% of Fe and 25% of Zn were removed, while at 1 mg/ml concentration, 19% of Fe and 52% of Zn removal occurred. A combination of bioleaching and biosurfactant in the cycling treatment process enhanced metal removal efficiency and reached up to 36% for Fe and 63–70% for Zn.
Dahrazma and Mulligan [16] conducted their experiment with the objective to estimate the Cu, Zn, and Ni removal efficiency of rhamnolipid in a continuous flow configuration. The effect of process parameters such as concentration of rhamnolipids and the additives, time, and solution flowrate on the column performance have been analyzed. The removal of metal ions was up to 37% of Cu, 13% of Zn, and 27% of Ni when rhamnolipid without additives was applied. Addition of 1% of NaOH to 0.5% of rhamnolipid enhanced the Cu removal up to four times as compared to 0.5% rhamnolipid solution alone.
4.10 Bioeconomics of Metal Remediation Using Biosurfactants
In recent times, the developments of the “bioeconomy” have been promoted by most of the world's developing and developed countries. The bioeconomy policies and strategies have been formulated by the scientific communities to reach this sustainable goal. A strong support for this thoughtful concept was provided by the Global Bioeconomy Summit organized in Berlin in the year 2015, which gave the chance to the bioeconomic experts and stakeholders from more than 50 countries to come together and discuss their critical views on a stated smoldering topic. In the summit, it was declared that nothing has a unified definition of the bioeconomy. However, experts agreed on a common understanding of the bioeconomy as the “knowledge‐based production and utilization of biological resources, innovative biological processes and principles to sustainably provide goods and services across all economic sectors.”
In the present review article, authors thoroughly studied the bioeconomy of biosurfactants production and utilization. With more and more stringent regulations on greener processes and catering to the huge demand, biosurfactants form a major share of the surfactant market. The global biosurfactant market in 2013 was 344 068.40 tons and had been expected to reach 461 991.67 tons by 2020, growing at a CAGR of 4.3% from 2014 to 2020 [73]. Revenue generation of the biosurfactant market was found to be over $1.8 billion in 2016 and is expected to reach $2.6 billion by 2023 (540 ktons by 2024), with the rhamnolipid market set to witness a gain of over 8% [74]. Some other market research reports showed the global biosurfactant market at over 5.52 billion by 2022, at a CAGR of 5.6% from 2017 to 2022 [75]. At the present time, Europe is rising and is projected to prolong to rise as the biggest market (nearly 53%) followed by the United States, mainly due to stricter regulatory guidelines in the region. In the meanwhile, the growing wakefulness and infrastructures in Asian countries is making them a rising consumer of biosurfactants. With the detergent industry leading the product application sector, sophorolipids among all different type of biosurfactants were found to have the largest global market share. The Germany‐based company BASF and Belgium Company Ecover have emerged as the top two biosurfactants producers in the surfactant market. Some other prominent companies involved in biosurfactant production and supplies are MG Intobio, Urumqui Unite, Saraya, Sun Products Corporation, Akzo Noble, Croda International PLC, Evonik Industries (Germany), Mitsubishi Chemical Corporation, and Jeneil Biosurfactant [74, 76]. On the other hand, in spite of the huge market demand, biosurfactant production is not as competitive as its synthetic counterparts. Therefore, economizing the biosurfactant production process assumes significance in order to sustain the market for these compounds in the current environmentally fragile scenario and long‐term sustainable development.
4.11 Conclusion
This chapter reflects detailed information on the utilization of biosurfactants as a potential substitute in the heavy metal ions bioremediation process from the polluted environment. Designing the new strategies and technologies is the need of society in order to minimize the biosurfactant production cost at a commercial scale and make the production process economically competitive. The biosurfactants formation costs can be decreased by lowering the number of agro‐industrial mistakes and the waste that treatment uses up. Agro‐industrial waste‐based biosurfactant generation renders another option for cheap and commercially viable biosurfactant production. For various applications, biosurfactants moved to generally regarded as safe (GRAS) microorganisms like lactobacilli and yeasts, which have astounding promise. However, significantly more research is now required in this field.
The production and commercial scale application of biosurfactant molecules remains a testing subject, as the planning of an irrefutable item is influenced by various key factors. For the utilization of biosurfactants in various areas, the rules and directions should be detailed. It is very much expected that in the near future such types of microbial strains have been synthesized using genetic engineering techniques that large‐scale production using crude materials as well as their industrial scale application will be possible. In terms of lowering the cost of biosurfactant production, these discussed strategies could prove to be the most economical ones. A stricter positioning of these structures is, therefore, an authoritative step toward production enhancement, production procedure economization, and establishing an economically competitive and successful biosurfactant market, as well as addressing the solid waste disposal issue by efficient conversion of low‐cost solid industrial and agricultural waste into revenue generating value‐added products.
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