Circular-Economy-Oriented Medium-Chain Fatty Acid Production from Organic Wastes via Chain Elongation: Artificial Regulation and Resource-Loop Pathways

• • CE via RBO converts short-chain carboxylates (e.g., acetate, lactate) into MCFAs (caproate, caprylate) with higher energy density and hydrophobicity, enabling carbon and electron recovery from organic wastes; process yields depend on electron donor supply and microbial community structure. • • Natural mixed-culture CE systems are limited by electron donor competition, propionate accumulation, product toxicity, and unstable continuous operation; artificial regulation (e.g., quorum sensing, iron-carbon enhancement) can improve MCFA production, as demonstrated by studies showing enhanced caproate synthesis via quorum sensing signals (e.g., autoinducer-2) and biofilm formation. • • Product separation remains a bottleneck; membrane electrolysis and electrodialytic separation have been explored for in-line and selective phase separation of medium-chain carboxylic acids, with semi-pilot scale studies reporting extraction efficiencies that justify further scale-up. • • Techno-economic and life cycle assessments are essential to validate the circular economy benefits; future work must address continuous-flow stability, separation costs, and process integration to achieve industrial viability.