Fresh and saline wastewater valorisation to natural flocculants: effect of COD/N ratio on polymer recovery and quality

In this study, we demonstrate simultaneous industrial wastewater treatment with the recovery of microbial extracellular polymeric substances (EPS) as effective and eco-friendly flocculants. EPS were produced from two membrane reactors (MBRs), respectively treating fresh (FW) and saline (Sal) synthetic wastewater from biodiesel and (bio)ethanol industries. The MBRs were operated under N rich (COD/N 5 and 20) and limited (COD/N 60 and 100) conditions to investigate the effect of N limitation on the process performance, EPS recovery, composition, molecular weight and charge density. N limitation had a significant impact on the EPS recovery. EPS produced under N limited condition had higher biopolymer molecular weight compared to EPS produced under excess N. These results demonstrate the potential of high strength industrial wastewater as suitable candidates to produce useful and effective bioflocculants.