Mixed microbial culture-derived flocculant overproduction from fermented waste streams in membrane and chemostat bioreactors as novel pathway for organics valorization

Volatile fatty acids (VFAs) from fermented wastewater are valuable biopolymer precursors. While microbial conversion of VFAs into polyhydroxyalkanoates (PHAs) is widely studied, their conversion into extracellular polymeric substances (EPS)-based flocculants remains largely unexplored. This study investigates EPS production from VFA-rich synthetic wastewater using mixed microbial cultures (MMC) under EPS-overproducing conditions i.e., solids retention time (SRT) of 3 days and nitrogen limitation. A continuous stirred-tank reactor (CSTR) and a membrane bioreactor (MBR) were compared under these conditions to assess the influence of process configuration on EPS yields, composition, and flocculation performance. VFA conversion was relatively high (∼80%) in the CSTR, but lower in the MBR (90%) with Ca 2+ as coagulant, comparable to commercial polyacrylamide (PAM, 92%), regardless of EPS type. These findings show EPS-flocculant production by MMC from VFA-rich wastewater, offering a sustainable route to convert waste carbon into functional biopolymers and support resource recovery and green flocculants development.