Biosurfactants in wastewater treatment: recent advances in agro-waste valorization, production technologies, and environmental remediation

Industrial, agricultural and municipal effluents are contaminated with a variety of pollutants, including hydrocarbons, heavy metals, dyes, pharmaceuticals and pathogenic microorganisms that have a great impact on the environment and on public health. Typical treatment technologies are expensive, pollute the environment as secondary pollutants, and are not very effective at remediating hydrophobic and persistent contaminants. Biosurfactants have proven to be eco-friendly alternatives, due to their biodegradability, they are low in toxicity and they possess surface activity along with the ability to improve the solubilization, emulsification and microbial degradation of the contaminant. This review critically discusses the recent developments in biosurfactant production by utilizing renewable agro-industrial wastes as sustainable feedstocks, emphasizing the roles of carbon source, biomass pretreatment methods, systems for microbial fermentation and optimization of the process for enhancing the production efficiency. Moreover, the review extensively covers the mechanisms involved in the uptake of hydrocarbons, heavy metals and other recalcitrant contaminants from wastewater using biosurfactants. The recent advancement in downstream processing such as acid precipitation, solvent extraction, membrane-based purification and foam fractionation is discussed regarding the recovery performance, economic viability and environmental impact. The existing challenges such as production costs, scaling up the process, product variability, and commercialization hurdles are also discussed along with the emerging solutions such as metabolic engineering, integrated biorefineries, and circular bioeconomy. In summary, this review has highlighted the increasing capability of biosurfactants as viable and sustainable wastewater treatment agents for the next generation of wastewater treatment technologies.