Browsing by Author "Song, Lianfa (TTU)"
Now showing 1 - 8 of 8
- Results Per Page
- Sort Options
Item A concise analytical model for the ideal reverse osmosis desalination processes(2023) Song, Lianfa (TTU)Permeate recovery is a key parameter that plays a central role in the performance assessment and optimization of reverse osmosis processes. It remains a great challenge for engineers in the field to determine the recovery conveniently and accurately from the basic parameters of a membrane system. A concise analytical model is presented here that, without the need for the empirical or fitting coefficients and tedious numerical calculation, links the recovery of a reverse osmosis process rigorously to three basic parameters: the feed water salt concentration, the characteristic of membrane process, and the driving pressure. A graphical solution method to the model is also introduced to find out the recovery effortlessly. The concise model and graphical method are demonstrated under various conditions as a powerful tool for the performance simulations and improvement of reverse osmosis processes.Item Accurate Determination of Electrical Potential on Ion Exchange Membranes in Reverse Electrodialysis(2021) Sun, Yuting (TTU); Song, Lianfa (TTU)Reverse electrodialysis is a promising membrane technology to generate energy from controlled mixing of water streams of different salinities. Electrical potentials generate on the ion exchange membranes (IEMs) when selective transport of cations and anions across the membranes driven by concentration difference. The accurate determination of the potentials developed on the IEMs is critical to fairly assess the feasibility of the technology. The Nernst–Planck–Poisson (NPP) equations for IEMs (the membranes with fixed charge) were solved numerically with the boundary updating scheme. The validity of this numerical method was verified by the identical values of Donnan potential obtained with the well-established analytical methods. The suitability and applicability of the classic Teorell–Meyer–Siever (TMS) model were assessed by comparison to the simulation results from the numerical method.Item Characterization of the fouling layer on the membrane surface in a membrane bioreactor: Evolution of the foulants’ composition and aggregation ability(2019) Yan, Linlin; Li, Ruixue; Song, Yu; Jia, Yanping; Li, Zheng; Song, Lianfa (TTU); Zhang, HaifengIn this study, the characteristics of membrane foulants were analyzed with regard to morphology, composition, and aggregation ability during the three stages of transmembrane pressure (TMP) development (fast–slow–fast rise in TMP) in a steady operational membrane bioreactor (MBR). The results obtained show that the fouling layer at the slow TMP-increase stage possessed a higher average roughness (71.27 nm) and increased fractal dimension (2.33), which resulted in a low membrane fouling rate (0.87 kPa/d). A higher extracellular DNA (eDNA) proportion (26.12%) in the extracellular polymeric substances (EPS) resulted in both higher zeta potential (-23.3 mV) and higher hydrophobicity (82.3%) for initial foulants, which induced and increased the protein proportion in the subsequent fouling layer (74.11%). Furthermore, the main composition of the EPS shifted from protein toward polysaccharide dominance in the final fouling layer. The aggregation test confirmed that eDNA was essential for foulant aggregation in the initial fouling layer, whereas ion interaction significantly affected foulant aggregation in the final fouling layer.Item Decolorization and Mineralization of Rhodamine B in Aqueous Solution with a Triple System of Cerium(IV)/H2O2/Hydroxylamine(2018) Wang, Shengli; Jia, Yanping; Song, Lianfa (TTU); Zhang, Haifeng (TTU)Hydroxylamine (HA) can react with hydrogen peroxide (H2O2) to generate hydroxyl radical (HO•), but the reaction rate between them is very slow (2.2 × 10-4 M-1 s-1). We propose a new system to accelerate the formation of aminoxyl radical (NH2O•) by the addition of cerium [Ce(IV)] to induce the continuous production of HO• through reaction with H2O2. We also investigate the decolorization and mineralization of rhodamine B (RhB) and mechanism in the Ce(IV)/H2O2/HA system. The initial pH plays a significant role in decolorization of RhB. In this work, observation of the rapid decolorization process after 60 min revealed that approximately 80% of RhB was degraded at the initial pH of 4.0. The HO• radicals were considered as the primary reactive oxidant in the system, during its investigation through coumarin capturing, benzoic acid capturing, and radical quenching experiments. The results of the present study suggest that the addition of Ce(IV) can greatly enhance the production of HO•, and the rapid decolorization and mineralization of RhB can occur through the Ce(IV)/H2O2/HA system at acidic pH conditions.Item Metastable state of water and performance of osmotically driven membrane processes(2019) Zhang, Haifeng; Wang, Jie; Rainwater, Ken (TTU); Song, Lianfa (TTU)Semipermeable membranes play critical roles in many natural and engineering systems. The osmotic pressure is found experimentally much less effective than the hydraulic pressure to drive water through the membrane, which is commonly attributed to the internal concentration polarization (ICP) in the porous layer of the membrane. In this study, it has been shown that a necessary condition for the osmotic pressure to be effective is water continuity across the entire membrane thickness under negative pressure, i.e., the water inside the membrane remains in a metastable state. However, the metastable state of water cannot be maintained indefinitely, and cavitation will undoubtedly occur in the osmotically driven processes. Collapse of the water metastable state was suggested for the first time to be a more important and fundamental reason for the low water fluxes in the osmotically driven membrane processes.Item Modeling and Optimization of Membrane Process for Salinity Gradient Energy Production(2021) Song, Lianfa (TTU)When hydraulic pressure was added on the feed side of the membrane in the otherwise conventional pressure retarded osmosis (PRO) process, the production rate of the salinity gradient energy could be significantly increased by manipulating the hydraulic pressures on both sides of the membrane. With hydraulic pressure added on the feed side of the membrane, much higher water flux could be obtained than that under the osmotic pressure of the same value. The osmotic pressure of the draw solution, instead of drawing water through the membrane, was mainly reserved to increase the hydraulic pressure of the permeate. In this way, orders of magnitude higher power density than that in the conventional PRO can be obtained with the same salinity gradient. At the optimal conditions, it was demonstrated that the energy production rates that were much higher than the economical breakeven point could be obtained from the pair of seawater and freshwater with the currently available semipermeable membranes.Item Quantitative analysis of membrane fouling mechanisms involved in microfiltration of humic acid-protein mixtures at different solution conditions(2018) Sun, Chunyi; Zhang, Na; Li, Fazhan; Ke, Guoyi; Song, Lianfa (TTU); Liu, Xiaoqian; Liang, ShuangA systematical quantitative understanding of different mechanisms, though of fundamental importance for better fouling control, is still unavailable for the microfiltration (MF) of humic acid (HA) and protein mixtures. Based on extended Derjaguin-Landau-Verwey-Overbeek (xDLVO) theory, the major fouling mechanisms, i.e., Lifshitz-van der Waals (LW), electrostatic (EL), and acid-base (AB) interactions, were for the first time quantitatively analyzed for model HA-bovine serum albumin (BSA) mixtures at different solution conditions. Results indicated that the pH, ionic strength, and calcium ion concentration of the solution significantly affected the physicochemical properties and the interaction energy between the polyethersulfone (PES) membrane and HA-BSA mixtures. The free energy of cohesion of the HA-BSA mixtures was minimum at pH = 3.0, ionic strength = 100 mM, and c(Ca2+) = 1.0 mM. The AB interaction energy was a key contributor to the total interaction energy when the separation distance between the membrane surface and HA-BSA mixtures was less than 3 nm, while the influence of EL interaction energy was of less importance to the total interaction energy. The attractive interaction energies of membrane-foulant and foulant-foulant increased at low pH, high ionic strength, and calcium ion concentration, thus aggravating membrane fouling, which was supported by the fouling experimental results. The obtained findings would provide valuable insights for the quantitative understanding of membrane fouling mechanisms of mixed organics during MF.Item Water transport in reverse osmosis membranes is governed by pore flow, not a solution-diffusion mechanism(2023) Wang, Li; He, Jinlong; Heiranian, Mohammad; Fan, Hanqing; Song, Lianfa (TTU); Li, Ying; Elimelech, MenachemWe performed nonequilibrium molecular dynamics (NEMD) simulations and solvent permeation experiments to unravel the mechanism of water transport in reverse osmosis (RO) membranes. The NEMD simulations reveal that water transport is driven by a pressure gradient within the membranes, not by a water concentration gradient, in marked contrast to the classic solution-diffusion model. We further show that water molecules travel as clusters through a network of pores that are transiently connected. Permeation experiments with water and organic solvents using polyamide and cellulose triacetate RO membranes showed that solvent permeance depends on the membrane pore size, kinetic diameter of solvent molecules, and solvent viscosity. This observation is not consistent with the solution-diffusion model, where permeance depends on the solvent solubility. Motivated by these observations, we demonstrate that the solution-friction model, in which transport is driven by a pressure gradient, can describe water and solvent transport in RO membranes.