Resource Recovery from Wastewater By Directing Microbial Metabolism Toward Production of Value-added Biochemicals

Transitioning wastewater treatment from mere pollutant removal to resource recovery necessitates exploiting the metabolic capabilities of microbial communities. Studies suggest that under low-oxygen conditions, microbes activate oxygen-responsive regulons that suppress the tricarboxylic acid (TCA) cycle, diverting carbon flux towards biosynthetic pathways and accumulating valuable organic metabolites. We hypothesized that dynamically altering dissolved oxygen levels in activated sludge would disrupt aerobic metabolic equilibrium, enhancing the production of valuable biochemicals like amino acids and fatty acids. To test this, batch experiments were conducted with activated sludge under constant aeration and rapid cycling between oxygen-rich and oxygen-poor states. Fluctuating oxygen concentrations between 0 and 2 mg/L significantly increased valuable biochemical production compared to constant aeration ( P <0.05). Continuous oxygen perturbations increased free amino acids by 35.7±7.6% and free fatty acids by 76.4±13.0%, while intermittent perturbations with anoxic periods enhanced free amino acids by 42.4±8.1% and free fatty acids by 39.3±7.7%. Notably, 14 standard amino acids showed significant increases, and most fatty acids had carbon chain lengths between C12-C22. Mechanistically, compared to stable oxygen, oxygen perturbations activated the FNR and ArcA regulons, resulting in lower relative abundances of TCA cycle enzymes such as malate dehydrogenase, isocitrate dehydrogenase, and 2-oxoglutarate dehydrogenase, while higher relative abundances of amino acid (ilv cluster) and fatty acid (acc cluster) biosynthetic enzymes. Our findings demonstrate that introducing controlled oxygen fluctuations in wastewater treatment can enhance the biochemical value of activated sludge with minimal process modifications, facilitating resource recovery.