smooth cost‐effective biosurfactant production and application.
4.8.1 Raw Material: Low Cost from Renewable Resources
In their natural environment, the microbial population produces surface‐active agent in extremely minute quantities. Keeping in mind these microbial behaviors, researchers try to maximize the biomolecule yield and extract more and more concentrations of highly efficient biosurfactants.
In lowering the overall production cost of biosurfactants, a selection of suitable and efficient low‐cost raw materials is important. Raw materials with higher concentrations of carbohydrate, nitrogen, and lipids highlight the necessity for biosurfactants in commercial production. Utilization of agricultural wastes and byproduct materials that are available in abundant quantity along with the benefit of reduced environmental pollution chances serve as the best raw material for biosurfactants. In a study conducted by Ashby et al. [61] on the effect of raw materials on biosurfactant cost, the authors found that approximately 75% of the total operating cost accounted for 90.7 million kg of sophorolipid production biosurfactant was due to glucose and oleic acid as the raw materials. The sophorolipid production costs vary depending on the raw material used; for example, when glucose and high oleic sunflower oil were used, the cost was estimated to be $2.95/kg and when glucose and oleic acid were used, it was reported to be $2.54/kg. This estimated high cost of sophorolipids production can be reduced after replacing the costly substrate with a low‐cost industrial and agro‐based byproduct. In another study by Rodrigues et al. [62], authors utilized low‐cost materials for production of biosurfactants and the yields were increased by 1.5 times to that of the original cost and a 60–80% reduction in the medium cost was observed.
4.8.2 Production Process: Engineered for Low Capital and Operating Costs
Currently, only very few biosurfactants have been used in metal ion remediation processes on a commercial scale due to lack of cost‐effective production processes. Due to the high costs of producing biosurfactants, their industrial application has been hindered.
Biosurfactant production on a large scale seemed to be very effective, but there is an urgent need to overcome competitiveness with their synthetic counterparts. Scientists made few attempts to develop large‐scale biosurfactants. The Bacillus subtilis FE‐2 strain has been used by Veenanadig et al. [50] to produce biosurfactants in a packed column bioreactor with a volumetric capacity of 30 l. In another study conducted by Daniels et al. [63] for large‐scale production of rhamnose and 3‐hydroxydecanoic acid from Pseudomonas sp., they claimed, in their patent, to produce in a defined culture medium that contained corn oil as a carbon source a high level of rhamnolipids at a concentration from about 30 g/l to about 50 g/l.
4.8.3 Improved Bioprocess Engineering
Process optimization plays a crucial role in cost reduction of large‐scale biosurfactant production. Synthesis of biosurfactant can be categorized into four foremost types:
1 Biosurfactant production associated with the growth medium and substrate utilization.
2 Under a growth‐limiting condition, biosurfactant production, e.g. P. aeruginosa shows an overproduction of biosurfactants when nitrogen and iron are limited.
3 Resting or immobilized cell utilization in biosurfactant production. This type of biosurfactant production shows high efficiency because microbial cells keep using a carbon source only for biosurfactant synthesis and not for multiplication, thus helping to reduce the production cost.
4 Precursor addition for biosurfactant production. The quality and quantity of biosurfactant polymer influenced chemical and physical parameters, and the type of carbon and nitrogen source along with their ratios in the culture media [64].
4.8.4 Strain Improvement: Engineered for Higher Yield
In a study, Kosaric et al. [65] suggested four factors to reduce the cost of biosurfactants production. The first one was the type of microbes (selected, adapted, or engineered for higher yields). The second one was the nature of reaction condition (selected, adapted, or engineered for low capital and operating costs). The third one was the growth media composition and raw material nature and the fourth one was the process byproducts (minimum or managed as saleable products rather than as waste). In order to make commercially viable biosurfactants, it is important to improve and optimize the reaction condition using bioprocess engineering along with the use of hyperproducing microbial strain. To economize the production process and to obtain products with better commercial characteristics, the availability of hyperproducer strains and recombinants is important.
4.8.5 Enzymatic Synthesis of Biosurfactants
Enhanced enzyme productivity in microbes after genetic modification for enhanced biosurfactants production has been used by scientists to improve the productivity‐to‐cost ratio. The effectiveness and efficiency of enzymes have been maximized through the use of biotechnological techniques. The specificity of microbial enzymes, their catalytic properties, and mode of action can be altered and modified into more effective forms using these techniques.
4.9 Application of Biosurfactant for Heavy Metal Remediation
In the last few decades, many studies have been conducted and published by the scientific communities on biosurfactant production and remediation application. Due to the vast variation in chemical composition, their eco‐friendly behavior, and wide range of applications in various processes, biosurfactants are utilized extensively in many sectors, including hydrophobic organic compounds and heavy metal ions remediation, enhanced oil recovery, and cosmetics and pharmaceutical sectors, etc. In the present review article, authors pay attention to the biosurfactant application for remediation of heavy metals (Table 4.3).
Table 4.3 Heavy metal removal efficiency of different biosurfactants.
| Organism | Biosurfactant type | Contaminated environment | pH | Temperature (°C) | Metals | Efficiency | References |
|---|---|---|---|---|---|---|---|
| Commercial | Rhamnolipid | Soil | 6.5 | 25 | Cu | 37 | Dahrazma and Mulligan [16] |
| Ni | 33.2 | ||||||
| zn | 7.5 | ||||||
| Torulopsis bombicola | Sophorolipid | Soil | 5.4 | — | Cu | 25 | Mulligan et al. [17] |
| Zn | 60 | ||||||
| Bacillus subtilis | Surfactin | Cu | 15 | ||||
| Zn |
6
|