Interface interaction between silica and organic macromolecule conditioned forward osmosis membranes: Insights into quantitative thermodynamics and dynamics.

Silica scaling is a rising concern in forward osmosis membrane-based water treatment process. The coexistence of ubiquitous organic macromolecules causes complex silica scaling. The silica scaling mechanism on the surface of the organic conditioned membrane remains unclear. An integrated multi scale thermodynamic and dynamic approach was used in this study to provide in-depth insights into the binding effect at the interface between the silica and the organic conditioned membrane at the molecular level. Sodium alginate (SA) was used as the model polysaccharide, bovine serum albumin (BSA) and lysozyme (LYZ) were chosen as two oppositely charged proteins. The results show that the silica scaling degree of different organic conditioned membranes follows the order LYZ > BSA > SA. The binding strength between silica and organic macromolecules and the membrane surface charge are the major factors governing the degree of silica scaling. Quartz crystal microbalance with dissipation (QCM-D), isothermal titration calorimetry (ITC), and extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) model analyses were conducted to quantify the binding capacity of silica to the organic conditioned membrane. The LYZ conditioned membrane exhibits the highest affinity for silica adsorption, and electrostatic interaction was the main molecular interaction force. This study provides fresh insights into how silica and an organic conditioned membrane interact and induce silica scaling, providing new information on potential mechanisms and control strategies to prevent membrane scaling.

Deciphering mono/multivalent draw solute-induced microbial ecology and membrane fouling in anaerobic osmotic membrane bioreactor.

Anaerobic osmotic membrane bioreactor (AnOMBR) attracted attention due to high quality effluent production with low energy demand, and draw solute has significant effect on the system performance. However, the mutual relationship between draw solute-induced salinity accumulation and microbial community had many unknown questions to be solved. This study purpose was to construct two AnOMBR to compare the impact of draw solutes of NaCl and MgCl2 on the dynamic change of microbial ecology and membrane fouling. The result indicated that the draw solute of MgCl2 caused less salinity and more membrane biofouling than that of the draw solute NaCl. Multiple microbiological analysis methods were applied to discover keystone species related to the conductivity change and membrane fouling, especially for the MgCl2-AnOMBR system. It was found that draw solute NaCl could benefit the growth of Proteobacteria to become the most abundant phylum to affect the membrane fouling, while Mg2+ introduction could stimulate the growth of NS9, Hydrogenphilaceae and Pedosphaeraceae to potentially cause the biofouling. Furthermore, phylogenetic molecular ecological networks (pMENs) deeply analyzed the microbial structure difference under Na+ and Mg2+ introduction, and indicated that the family Lentimicrobiaceae and Candidatus_Kaiserbacteria were the keystone species in NaCl-AnOMBR, while two genus Anaerolinea and SWB02, and two families Saprospiraceae and NS9 were discovered to have key effect in MgCl2-AnOMBR due to their strong extracellular polymeric substances (EPS) production ability for survival of other microorganisms. This study was significant to give microbial targets under the impact of various draw solutes, as the reference for the engineers to further investigate how to improve the microbial structure to enhance AnOMBR performance and inhibit the membrane biofouling.

Interaction between humic acid and silica in reverse osmosis membrane fouling process: A spectroscopic and molecular dynamics insight.

Combined organic and inorganic fouling is a primary barrier constraining the performance of reverse osmosis (RO) membrane. In this work, we conducted a systematic study focusing on the synergetic fouling effects of silica and humic acid (HA) in RO process, and found the critical silica concentration where the fouling pattern changed qualitatively. When the silica concentration was lower than 6 mM at a typical HA concentration of 50 mg·L-1, no severe fouling was observed, while silica reaching this critical point could cause severe synergetic fouling with HA. Concentrated silica above the critical point acted as the prior foulant with marginal fouling effect caused by HA. A variety of solutions and surface-based characterizations were performed to elucidate the synergistic fouling responsibility for silica and HA. Our study suggests that the carboxylic groups from HA formed hydrogen bonds with silica hydrate, inducing silica adsorption onto HA aggregates at low silica particle concentrations. The HA network was bridged together to form large foulants due to the silica-silica interaction above the silica critical concentration. These mechanisms were further confirmed by molecular dynamics simulations. This study provides an in-depth insight into the combined organic-inorganic fouling and can serve as a guideline to optimize feed conditions in order to mitigate fouling of RO in wastewater reusing industry.

Evaluating the performance of inorganic draw solution concentrations in an anaerobic forward osmosis membrane bioreactor for real municipal sewage treatment.

Sewage can become a valuable source if its treatment is re-oriented for recovery. An anaerobic forward osmosis membrane bioreactor (AnOMBR) was developed for real municipal sewage treatment to investigate performance, biogas production, flux change and mixed liquor characteristics. The AnOMBR had a good treatment capacity with removal ratio of chemical oxygen demand, ammonia nitrogen, total nitrogen and total phosphorus more than 96%, 88%, 89% and almost 100%. Although high DS concentration increased the initial flux, it caused rapid decline and poor recoverability of FO membrane flux. Low DS concentration led to too long hydraulic retention time, thus resulting in a low reactor efficiency. Additionally, it was observed that salt, protein, polysaccharide and humic acid were all accumulated in the reactor, which was not conducive to stable long-term operation. Based on the characteristics of membrane fouling, salt accumulation and AnOMBR performance, the optimal DS of 1 M NaCl solution was selected.

Surface charge regulation of reverse osmosis membrane for anti-silica and organic fouling.

Dissolved silica and organic matter are major foulants in reverse osmosis (RO) in brackish water treatment. Though the mechanism of inorganic and organic fouling has been clear, combined silica-organic fouling-resistant membrane have been poorly investigated. In this study, we fabricated membranes with different surface charge. More negatively surface charged membrane (-COOH), acrylic acid (AA) membrane was fabricated through redox free radical grafting method. Ethylamine (EA) and ethylenediamine (ED) membranes with neutral or less negative surface charge were fabricated through -CH3 or -NH2 functional groups grafting. The surface modified membranes were characterized in terms of physicochemical properties and antifouling performance. Compared with the pristine membrane, all the modified membranes possessed better salt rejection without sacrificing water permeability. The AA membrane also showed better antifouling property and higher water flux recovery after physical rinsing. On the other hand, fouling on the EA and ED membranes were aggravated. Unlike the gel-like foulant structure on the EA and ED membrane surfaces, the AA membrane presented more disordered granular structure. Analysis of fouling layer has also proved that there was less silica scaling and organic foulants on the AA membrane surface. Despite the outstanding hydrophilicity of the AA membrane, its antifouling property was mainly attributed to the more negative surface charge, according to regression between flux decline and membrane characteristics. Importantly, we proposed that electrostatic interaction was the dominant fouling mechanism in the combined silica-organic fouling. With more negative surface charge, the AA membrane was prone to prevent foulants from depositing and aggravating, so as to mitigate membrane fouling. Our research provides a simple and practical approach to RO membrane fabrication for anti-inorganic and organic.