Journal of Membrane Science Letters最新文献

Fabricating acid resistant nanofiltration (NF) membranes with precise solute separation performance is highly demanded for acidic wastewater treatment but remains a challenge. Herein, we propose a facile strategy for preparing dually charged acid resistant NF membranes with both high cations and anions rejections via a two-layer reverse interfacial polymerization (r-IP) process. Organic monomers of trimesoyl chloride (TMC) and 1,4-phenylene diisocyanate (PPDI) are firstly applied to react with 3-aminobenzenesulfonamide (ABSA) to construct a negatively charged loose intermediate layer, followed by the r-IP of TMC/PPDI and polyethyleneimine (PEI) to engineer a dense positively charged top layer. The highly cross-linked polyurea (PU) formed by isocyanate and amine leads to an enhanced size sieving effect, and the well-arranged dually charged layer endows the membrane stronger electrostatic exclusion. The resultant membrane has 97.7% rejection of Na₂SO₄ and 93.0% of MgCl₂, and it exhibits fairly high rejections to various heavy metals, as well as impressive long-term stability after exposure to strong acid (10 wt% of H₂SO₄ for 400 h).

Accounting for concentration-polarization (CP) is critical for modeling solute transport in membrane separation processes. In a mixed-electrolyte solution, ions' CP is affected not only by diffusion and advection but also by electromigration. Yet, the classic film model, lacking an electromigration term, is frequently used for modeling ion CP. Often, ion CP is altogether neglected to reduce the computational load. Here, we study the CP of trace ions in a dominant salt solution, a case relevant for many reverse-osmosis and nanofiltration processes. First, we revisit the solution-diffusion-electromigration-film theory to obtain an analytical solution for the CP and membrane-transport of trace-ions in a dominant salt solution. Secondly, we consider limiting conditions relevant to reverse-osmosis and nanofiltration, from which we derive two compact equations that emerge as a seamless extension to the classic film theory. These equations can be used to account for the effect of electromigration on CP with minimal effort. Thirdly, we use our theory to quantify the effect of electromigration on ion CP in different dominant salt solutions. Finally, by analyzing two environmental membrane processes, we demonstrate how our theory deviates from the conventional one and quantify the implications on membrane scaling potential and the transport of ionic contaminants.

Detrimental biofilms on RO membranes remain a crucial challenge for seawater desalination. Comparative analysis of 16S rRNA gene amplicon sequencing data revealed differences and commonalities of biofilm communities associated with unit operations in the two largest seawater desalination facilities in the U.S., the Claude "Bud" Lewis Carlsbad Desalination Plant and the Tampa Bay Seater Desalination facility. At both plants, feedwater collected at a single time point was a poor indicator of the RO membrane communities, which showed far greater taxa diversity. The analysis of prefilter cartridges from the Carlsbad plant revealed similarly high taxon diversity as the RO module biofilms, with relevant differences. Algal sequences were enriched on the prefilter cartridges as were sequences representing Bdellovibrionota, which are predatory bacteria. Sequences representing opportunistic Gammaproteobacteria (i.e., Shewanella, Woesia) were present in significantly higher relative abundance on the RO membranes than in the prefilter cartridges, suggesting growth of certain taxa in the RO modules. Untargeted metabolomics distinguished intra- and inter-desalination plant biofilm samples, highlighting the potential value of this tool for biofilm monitoring. These findings underscore the value of omics tools for effective microbial monitoring, to understand biofouling dynamics within RO desalination plants, and to provide insight for the development of ecologically-informed biofilm control measures.