Critical evaluation of sustainable biosurfactants on the example of rhamnolipid and sophorolipid production from waste valorization: Challenges, industrial feasibility, and future perspectives

This review critically evaluates the sustainability-driven production, advantages, limitations, and industrial feasibility of rhamnolipids and sophorolipids, two of the most promising classes of biosurfactants. These amphiphilic biomolecules, derived from renewable substrates and agro-industrial residues, offer key benefits such as biodegradability, surface activity, and potential integration into circular bioeconomy strategies. However, despite their environmental appeal, their widespread adoption remains constrained by significant technological, economic, and regulatory barriers. Typical biosurfactant titers remain within 10–40 g L−1, and although yields exceeding 100 g L−1 have been reported, such results are mostly confined to optimized laboratory conditions. Among biosurfactants, rhamnolipids remain particularly challenging to scale up, with reported titers of 0.1–22.5 g L−1 and production costs of USD 5–1500 kg−1, far exceeding those of synthetic surfactants (USD 1–2 kg−1). Sophorolipids demonstrate higher potential, achieving ∼200–250 g L⁻¹ under laboratory conditions, yet they too face hurdles related to scalability, cost reduction, and regulatory approval. In addition to low productivity, biosurfactants exhibit sensitivity to environmental conditions such as pH and temperature, limiting their applicability in harsh industrial settings where synthetic surfactants remain more reliable. Their structural complexity, particularly in hydrophobic moieties, further complicates formulation stability and necessitates thorough toxicological and environmental assessments, as biological origin alone does not guarantee safety. Addressing these bottlenecks will require integrated strategies in strain engineering, process intensification, waste valorization, and downstream processing. Until such advances are realized, biosurfactant applications will likely remain confined to niche, high-value sectors where sustainability and biodegradability outweigh cost constraints. By providing a deep critical analysis of rhamnolipid and sophorolipid production within a sustainability framework, this review aims to clarify their realistic industrial potential and outline future strategies for scaling sustainable biosurfactant technologies.