Evaluation of Pressure-Driven Membrane Processes for Nutrients Recovery from Dilute Effluents

Results are presented from an ongoing R&D project, aiming at full utilization of dairy-industry effluents. Development of a membrane-based method is pursued, for treatment of digestate (after fermentation yielding bio-gas) to recover nutrients (N-NH4, P-PO4) and water for reuse/recycling or safe disposal. The performance is investigated herein of four commercial nanofiltration/ultra-low-pressure reverse osmosis membranes, employed in dead-end filtration mode, for nutrients recovery from solutions simulating the liquid digestate/effluent of an anaerobic membrane-bioreactor (AnMBR). Best-performing membranes, regarding nutrients’ rejection, were assessed within a sufficiently broad range of all key process parameters, including trans-membrane pressure and feed-composition. Further testing took place in a cross-flow set-up, simulating real operating conditions. For ~80% permeate recovery, the concentrate was significantly enriched in nutrients; i.e. compared to feed-solution, N-NH4 was concentrated twice, whereas P-PO4 was concentrated by 3- to 4-times. Research with real AnMBR effluent is on-going, for process improvements/optimization, mainly focusing on composition of concentrate/nutrients (for use in liquid fertilizers), membrane-fouling mitigation and quality of permeate/water for possible reuse.