Making Waves: Harnessing microbial stress responses for nanoparticle-enabled resource recovery

• Low-dose nanoparticles stimulate microbial extracellular polymer secretion. • EPS removal before digestion improves methane yield and sludge handling. • EPS–NP complexes are rich in nutrients and essential trace elements. • EPS–NP complex acts as a slow-release, biodegradable biofertilizer. • Approach supports circular bioeconomy and nutrient recycling goals. Engineered nanoparticles (ENPs) are increasingly present in wastewater systems and typically regarded as contaminants. This perspective explores a counterintuitive strategy: introducing low concentrations (≤5 mg/L) of ENPs, such as zinc oxide, copper oxide, or magnetite—into wastewater to stimulate microbial production of extracellular polymeric substances (EPS). EPS forms a protective matrix that binds metals and pollutants and can be selectively recovered prior to anaerobic digestion. While excessive EPS may impair digestion processes, early recovery enables its reuse as a biologically derived, slow-release fertilizer. These EPS–NP composites could deliver essential micronutrients in a controlled, biodegradable form. We propose a conceptual framework for this transformation, outlining technical feasibility, ecological risk, and regulatory considerations. Though not an experimental study, this work emphasizes the potential of microbial stress engineering as a tool for circular wastewater management. To our knowledge, this is the first framework proposing ENP-triggered EPS recovery for agricultural nutrient recycling.