Development of a crossflow nanofiltration process for polishing of wastewater by-product from biogas production processes

The growing adoption of biogas production from source-separated organics (SSOs) has resulted in a need for advanced treatment processes for the resulting liquid waste by-products. While previous studies have demonstrated the potential of using nanofiltration (NF) membranes to polish the outlet stream of a membrane bioreactor (MBR) in municipal wastewater applications, there is little known about the performance of such membranes to treat the more complex multi-component streams that result from the processing of SSOs. In this study, crossflow filtration experiments with three commercial flat-sheet NF membranes (NFS, NFX, NF90) were run on two batches of MBR permeate (identified as Batch A and Batch B) which were sourced four months apart from a biogas production facility. For each batch, there was a remarkable difference in performance of the three NF membranes, where a clear trade-off between permeate quality and recovery was observed. For example, the NF90 membrane gave the best permeate quality but the lowest recovery. Interestingly, the NFS permeate COD for Batch B was approximately 60 % lower than that for Batch A; it is believed that this was due to differences in the amount of ammonia between the two batches. This work bridges a technical gap in the water-energy nexus by demonstrating the viability of using NF technology to polish liquid waste streams from biogas production processes, while also highlighting their susceptibility to variable feed conditions caused by upstream process deviations.