Microbial Nanomaterials for Wastewater Treatment and Resource Recovery: A Critical Review of Circularity, Regeneration, and Technology Readiness

Microbial nanomaterials are increasingly investigated for wastewater treatment because microorganisms and their products can mediate nanoparticle synthesis, biomineralization, catalytic transformation, adsorption, membrane functionalization, and resource recovery. However, high contaminant-removal efficiency does not necessarily demonstrate circularity or technological viability. This critical review evaluates microbial nanomaterials according to their biological origin, treatment performance, resource-recovery potential, material recovery and regeneration, environmental safety, life-cycle and techno-economic performance, and technology readiness. Evidence was identified through structured searches of major scientific databases, with emphasis on quantitative studies using real wastewater, continuous operation, regeneration, and recoverable products. The strongest evidence for circular functionality was found in the microbial recovery of metals and metalloids, biologically regenerated reactive materials, immobilized biogenic nanoparticles, and reusable microbial–polymer systems. Nevertheless, most studies remain laboratory based, and complete mass balances, product-quality data, nanoparticle containment, long-term regeneration, life-cycle assessment (LCA) and treatment-specific techno-economic assessment (TEA) are uncommon. Benchmarking against activated carbon, ion exchange, membrane processes, and chemically synthesized nanomaterials shows that microbial systems currently offer specialized rather than universal advantages. Most reviewed technologies remain approximately at Technology Readiness Levels (TRLs) 2–5. Microbial nanomaterials therefore have the greatest potential as recoverable, regenerative, and resource-oriented components integrated with established wastewater-treatment infrastructure.