Resource recovery from digested manure centrate: comparison between conventional and aquaporin thin-film composite forward osmosis membranes

We compared the performance of conventional and aquaporin thin-film composite forward osmosis (FO) membranes (denoted as HTI and AQP membrane, respectively) for concentration of digested manure centrate. Results show that the two FO membranes were capable to concentrate digested centrate for resource recovery. During concentration of digested manure centrate, a cohesive fouling layer formed on the HTI membrane surface, resulting in more dramatic flux decline and less fouling reversibility in comparison to the AQP membrane. The two FO membranes exhibited effective and comparable rejection of bulk organic matter, total phosphorus, and heavy metals, leading to their notable enrichment in digested manure centrate. By contrast, ammonium nitrogen (NH₄⁺-N) was only retained by approximately 40% using the two FO membranes with a slightly higher retention by the HTI membrane, since it was less negatively charged. As a result, total nitrogen was ineffectively rejected by the two FO membranes. It is noteworthy that the HTI membrane also contributed to higher rejection of most antibiotics than the AQP membrane, possibly due to enhanced retention by the fouling layer and retarded forward diffusion. Results from this study evidence the outperformance of the AQP membrane as a new generation FO membrane over its conventional counterpart with respect to antifouling property, while further improvement in membrane selectivity, particularly of monovalent cations (e.g. NH₄⁺-N), is needed to advance FO applications in resource recovery from challenging waste streams.