Mechanistic Model for CaSO4 Fouling on Nanofiltration Membrane

One of the major limitations of nanofiltration (NF) in drinking water treatment is inorganic scaling. In this study, a mechanistic model has been proposed to describe the permeate flux decline process during CaSO4 scaling in NF. It has been observed that the permeate flux decline follows four distinct stages. At first stage, 22–30% flux is reduced due to concentration polarization. At the second stage, flux is not reduced, instead, nucleation of CaSO4 occurs. The major permeate flux decline (60–70%) occurred at the third stage due to CaSO4 cake formation. At the final stage, the system reached the steady state, where rate of CaSO4 deposition on the membrane is balanced by shearing caused by the increase of concentrate flow rate. Beyond this stage, the flux does not decrease significantly. At each stage, the concentration of the salt at the membrane surface was estimated. The maximum salt concentration was found at the initial stage of permeate flux reduction, which gradually decreases as the filtration proceeds.     

反渗透海水淡化技术应用

介绍了鞍钢股份有限公司鲅鱼圈钢铁分公司120 t/d反渗透海水淡化示范工程的总体设计、设备研制、选型及工艺。对反渗透海水淡化系统进行了连续运行和测试,结果表明,该系统运行参数稳定,设备运行正常,性能指标达到设计要求,淡化后的海水达到了GB5749-2006国家饮用水标准。     

Removal of 17β Estradiol and Fluoranthene by Nanofiltration and Ultrafiltration

With the recent emergence of endocrine disrupting compounds as an important potable drinking water and reclaimed wastewater quality issue, the removal of two estrogenic compounds (17β-estradiol and fluoranthene) by nanofiltration and ultrafiltration membranes was investigated. A less hydrophobic organic compound model species [parachlorobenzoic acid (PCBA)] was tested. 17β-estradiol (E2), fluoranthene, and PCBA were applied to the membrane in the presence and absence of natural organic matter (NOM). Both batch adsorption and dead-end stirred-cell filtration experiments indicated that adsorption is an important mechanism for transport/removal of relatively hydrophobic compounds, and is related to the octanol-water partition coefficient (KOW) values. All filtration measurements were performed approximately the same permeate flow rate in order to minimize artifacts from concentration polarization varied with different hydrodynamic operating conditions at the membrane interface. The percent removal by dead-end stirred-cell filtration ranged from 10 to >95% depending upon membrane pore size/hydrophobicity and presence/absence of NOM at an initial concentration ranging from 0.1 to 0.5 μM. Additional batch adsorption experiments with radio-label (3H) E2 at lower concentrations ranging 0.025 to 5 nM showed that E2 removal due to adsorption was independent of its initial concentration. Adsorption occurs both on the membrane surface and interior membrane pore surfaces. However, adsorption was insignificant for PCBA (log?KOW = 2.7), but removal presumably occurred due to electrostatic exclusion. Partition coefficients (log?K) of 0.44 to 4.86 measured in this study increased with log?KOW and membrane pore size.     

Improved Discharge Configurations for Brine Effluents from Desalination Plants

Sea water desalination plants discharge a concentrated brine effluent into coastal waters. Modern, large capacity plants require submerged discharges, in the form of a negatively buoyant jet, that ensure a high dilution in order to minimize harmful impacts on the marine environment. Existing design practice favors a steep discharge angle of 60° above horizontal, a practice based on limited and outdated laboratory data for dilutions at the level of maximum rise. Examination of more recent laboratory data and the parametric application of a jet integral model suggest that flatter discharge angles of about 30–45° above horizontal may have considerable design advantages. These relate to better dilution levels at the impingement location, especially if bottom slope and port height are taken into account, there is better offshore transport of the mixed effluent during weak ambient current conditions, and there is the ability to locate in more shallow water near shore.     

Simulations of Full-Scale Reverse Osmosis Membrane Process

Performance of a two-stage full-scale reverse osmosis (RO) process for a desalination plant in Florida was simulated with a mathematical model based on the principles of membrane transport and mass conservation. In this model, water flux at any point along the filtration channel is calculated locally according to the basic transport theory of RO membranes. The changes in cross-flow velocity and salt concentration along the filtration channel were determined using mass balance principles of water and salt. Simulations of the plant performance were compared with the in-plant observation data over a period of more than 300 days. The results showed that the model could adequately describe the performance of the full-scale RO process based on a few module and operating parameters. The study also revealed that salt rejection of a RO membrane changed with feed salt concentration. The osmotic pressure coefficient that fits best with performance of this plant was substantially lower than the value determined with the “rule of thumb” (i.e., osmotic pressure in psi ≈ 0.01×total dissolved solids in mg/L) and had to be determined specifically for the particular feed water being processed.     

Evaluation of Apparatus for Membrane Cleaning Tests

Membrane cleaning is critical to the operation of membrane processes. This paper studies the impact of using four different types of bench-scale membrane systems to assess the effectiveness of different cleaning steps after the filtration of colored river water. The systems are a stirred ultrafiltration (UF) cell, a SEPA cell, a small cross-flow (CF) cell, and a six-CF-cell-in-parallel system. The effect of cleaning frequency was also investigated. The comparison was implemented in terms of flux recovery, solute removal, solute resistance removal, and changes of contact angles. The stirred UF cell was only reliable and comparable in terms of flux and flux recovery results. The six-cell-in-parallel system requires further development due to their much lower flux. For cleaning at 30-min intervals, the cleaning efficiency of membranes was similar for the three CF systems. For cleaning intervals of 2 and 4 h did not statistically affect the flux recovery for the stirred UF cell and SEPA cell. There was some irreversible fouling that could not be restored completely by clean-in-place method even with rigorous chemical treatment.     

Thin-Layer Gravity Current with Implications for Desalination Brine Disposal

Measurements of stratification and dissolved oxygen (DO) illustrate a hypersaline gravity current with salt loads similar to a desalination plant brine discharge. Over a 48-h sampling period in August 2005, alternating cycles of high- and low-temperature hypersaline water were observed along the bottom of Corpus Christi Bay in Texas, coincident with low benthic DO and tidal flushing from an adjacent smaller bay. The gravity current underflow was typically less than 10% of the overall water depth. Strong salinity gradients prevented wind-mixing of the entire water column. Hypoxic and near-hypoxic conditions were associated with limited DO replenishment from the ambient water. High DO levels in the underflow source water did not deter the development of offshore benthic hypoxia. A quasi-Lagrangian analysis is used to evaluate the relationship between ambient mixing and lateral mixing within the underflow. The analysis is further applied to estimating DO demand rates in the hypersaline plume. Mixing between the ambient water and the underflow predominately occurs over the sloping bay boundary. Once the gravity current reaches the flatter section of the bay, mixing is substantially reduced and DO is progressively depleted at the bottom. The transit time of the underflow (i.e., residence time or isolation time for water near the bottom) and wind-mixing energy appear to be key factors governing stratification persistence and potential hypoxia development. The observations and analyses provide insight into possible fate, impacts, and open questions associated with similarly scaled salt loadings from a desalination plant into a shallow bay.     

一体化工艺在膜法海水淡化预处理中的应用

在概述海水淡化技术的主要应用工艺的基础上,分析了膜法海水淡化预处理工艺将气浮、沉淀、过滤等工艺组合使用的可能性。市政给水、废水处理领域的诸多工程实例表明,气浮、沉淀、过滤一体化预处理工艺,以其占地小,节省投资、运行成本等特点,在反渗透法海水淡化领域具有广阔的应用前景。     

高炉渣冲渣水余热回收应用于海水淡化工艺的研究

介绍了中国钢铁行业的余热分布和利用情况,重点介绍了目前高炉冲渣水余热的利用现状和存在的问题, 以及主要海水淡化方法和热源使用情况。指出从替换热源上着手能有效降低海水淡化成本,提出将高炉冲渣水的 热量回收用于海水淡化的新思路,从理论上分析了二者结合的可行性和效益。为沿海钢铁企业节能降耗、解决缺 水和降低海水淡化成本等问题提供参考。     

Modeling Water Movement and Flux from Membrane Pervaporation Systems for Wastewater Microirrigation

A mathematical model to predict the performance of a membrane pervaporation unit directly placed in the soil to reuse wastewater for agricultural microirrigation was presented. The model was formulated by combining the solution–diffusion and the resistance-in-series model for mass transport across the membrane thickness, the Richard’s equation for soil water movement and the van Genuchten function for soil hydraulic properties to predict the water permeate flux for different types of test soil over a wide range of process operating conditions. Its applicability was assessed by comparing to the experimental data collected using both hollow fiber (HF) bundles and corrugated sheets (CS) membrane modules made of a hydrophilic dense polymer. A good agreement was observed between the model predictions and the experimental measurements. Further analysis concluded that the water permeate flux were mainly controlled by the porosity, the particle-size distribution, and the residual water of the soil. The overall mass transfer resistances were estimated to be 1.2×1014 and 5.6×1013?s?Pa/m for the HF and CS modules buried in loam soil, respectively, which are different from those measured in sweeping air pervaporation tests. The soil resistance for water transport was 7.1×1013?s?Pa/m. It is believed that the model could be a valuable tool to refine the design and optimize the operation of the proposed membrane pervaporation system.     

Growth and Decay of Estuary Ice Cover

This paper presents a new vertical 1D finite-element model to simulate the growth and decay of an ice cover (columnar ice, snow ice, slush, and snow cover consolidation) over a winter season in a partially mixed mesotidal estuary. In this study, we present, discuss, and validate boundary conditions as well as test and optimize the numerical model. Predictions from the model were assessed against field observations of ice thicknesses and internal temperatures taken over 3?years. This paper explains why ice in the estuary is almost completely composed of freshwater. We demonstrate how a columnar ice sheet grows over the first half of the winter season and is then melted from underneath during the second half of winter, especially where currents are strong. We also demonstrate that significant snow ice may form over the second half of winter if the ice cover survives long enough by resisting mechanical breakup of spring tides in March.     

Removal of N-Nitrosamines and Their Precursors by Nanofiltration and Reverse Osmosis Membranes

Rejection of selected N-nitrosamines, a group of probable human carcinogens, and their precursors by nanofiltration (NF) and brackish water reverse osmosis (BWRO) membranes was evaluated using a bench-scale cross-flow filtration apparatus. The tested nitrosamines included N-nitrosodimethylamine, N-nitrosomethylethylamine, N-nitrosopyrrolidine, N-nitrosodiethylamine, N-nitrosodi-n-propylamine, and N-nitrosodi-n-butylamine. The target nitrosamine precursors included secondary amines such as dimethylamine, methylethylamine, diethylamine, and dipropylamine. Rejection of nitrosamines varied greatly depending on the tested membranes (9–75% for NF membranes and 54–97% for BWRO membranes) and the molecular weight of nitrosamines. Experimental data obtained with the BWRO membranes matched well with an irreversible thermodynamic model coupled with film theory. The model further suggested that effective diffusion of nitrosamines through the BWRO membranes is responsible for the relatively low rejections observed experimentally, and the aqueous diffusivity of nitrosamines could be used as an accurate measure of nitrosamine permeability through these membranes. The steady-state rejection of all the tested nitrosamine precursors reached over 98%. This study suggests that a strategy for membrane-based water treatment processes to reduce nitrosamines should consider the removal of precursors before nitrosamines are formed during subsequent disinfection and water distribution.     

钛制板式换热器在海水淡化中的应用

本文从板式换热器概述、钛制板式换热器产品系列、钛制板式换热器在海水淡化中的应用几方面进行了综述,并对钛制板式换热器在海水淡化中的应用前景进行了展望。     

我国海水淡化的现状与钛的应用

海水淡化是解决人类水资源危机的重要途径。重点介绍了蒸发法中的多级闪蒸、多效蒸发,以及膜法中的反渗透海水淡化方法,并分析了各种方法的优缺点、现状和发展方向;总结了世界范围内各种海水淡化装置中钛的应用情况,讨论了与铜管相比,钛管的性能、成本等指标的优劣性,着重分析了今后海水淡化方法及钛在海水淡化中应用的发展方向。分析认为,今后海水淡化产业在世界范围内的发展将更加迅速,中国也将成为海水淡化产业发展的主要市场之一;随着"十二五"规划对今后海水淡化原材料、装备制造自主创新率的明确要求,国产钛材在海水淡化产业中的应用必将迎来新的发展机遇。     

Cost Optimization of Nanofiltration with Fouling by Natural Organic Matter

An artificial neural network and genetic algorithm routine has been developed for predicting and optimizing membrane system performance. The model predicted system behavior in response to operating conditions of applied pressure and crossflow velocity. Artificial neural networks accurately modeled mechanisms involved in fouling of membranes by natural organic matter. The model correctly predicted the effects of calcium within the solution in exacerbating fouling, binding of the divalent calcium ions to the natural organic matter macromolecules, and the formation of complexes. The model also correctly predicted the role of increased pressure in inducing fouling and the reverse scenario of mitigating fouling with increased crossflow velocity. The model was applied to membrane plant design for determining cost-effective operations. The genetic algorithm routine searched the predictions of the system model to determine the optimal operating conditions. Fouling conditions induced by the presence of calcium resulted in escalating costs with increases in calcium concentration. Membrane-related cost components were shown to be a significant cost factor that is sensitive to operating conditions and represents a prime target for optimization.     

Experimental Studies on Vertical Dense Jets in a Flowing Current

Experiments were performed using three-dimensional laser-induced fluorescence on turbulent vertical dense jets in flowing currents typical of brine disposal from seawater desalination plants. The flows are complex and different phenomena can dominate at different locations and at different current speeds, indicating that predicting these flows numerically will be quite challenging. At low current speeds, the rising and falling flows are almost vertical with some interference between them and the bottom flow spreads upstream as a wedge. At higher current speeds the wedge is expelled; the ascending flow is still almost vertical, but the descending flow is more gradual so the jet impacts the lower boundary farther downstream. Dilutions at the terminal rise height and impact point increase with increasing current speeds. Cross-sectional profiles of tracer concentration are neither axially or self-similar. In the descending flow, at low or intermediate current speeds, the plume is much taller than it is wide, the peak concentration occurs much closer to the top, and fluid can detrain from the jet. At higher current speeds, the profiles initially approach radial symmetry, but develop a kidney shape due to formation of two counter-rotating vortices farther downstream. These vortices cause the jet to almost completely bifurcate after impacting the bottom.     

MED-TVC海水淡化系统在首钢京唐公司的应用

介绍了海水淡化的方法及适用范围.京唐公司日产12500 t低温多效海水淡化系统工艺流程,分析了热压缩器工作原理,自动控制系统的软、硬件组成以及网络架构的选择。     

Determination of Perchlorate Rejection and Associated Inorganic Fouling (Scaling) for Reverse Osmosis and Nanofiltration Membranes under Various Operating Conditions

This study focused on perchlorate (ClO4?) rejection and flux-decline in bench-scale cross-flow flat-sheet filtration for two reverse osmosis (RO) and two nanofiltration (NF) membranes with a natural water, and addressed estimation of precipitative fouling/scaling with inorganic salts and characterizations of inorganic fouling and antiscalants. Thus the study considered tradeoffs between productivity (increased recovery and flux) versus ClO4? rejection versus membrane fouling/scaling. In this study, the rejection of water quality parameters (cations, anions, dissolved organic carbon, UVA254, total dissolved solids) and flux-decline trends for four different membranes were investigated over a various range of operating conditions (i.e., J0/k ratio and recovery). Inorganic foulants on the membrane surface were analyzed by various methods (i.e., x-ray diffraction and scanning electron microscopy), and demonstrated inhibition effects of antiscalant. With increasing recovery and J0/k ratio, high productivity (flux) was achieved, however, the rejections of perchlorate and other water quality parameters decreased and the precipitative fouling/scaling potential of membranes increased. At the same operating conditions in the presence of an antiscalant, embodying phosphonate functional groups, flux decline trends for the four membranes indicated lower scale formation supported by the results of the fouled membrane characterizations.     

Hydrodynamic Stability of a Periodically Unsteady Swirling Jet

The stability characteristics of a jet with a low-frequency time-dependent periodic swirl are determined. An analytical dispersion relation for the perturbations is obtained and solved numerically. Growth rates and celerities determined from this formulation are compared with predictions based on applying steady state analysis to instantaneous velocity profiles, i.e., the quasisteady approach. The results show that periodic unsteadiness in the swirl causes variations in the growth rates and celerities of the unstable modes. Furthermore, it is shown that the quasisteady approach is not applicable and fails to predict the magnitudes of these variations.     

Evaluation of Membrane Processes for Reducing Total Dissolved Solids Discharged to the Truckee River

Truckee Meadows Water Reclamation Facility (TMWRF) is a 150,000?m3/day (40?mgd) tertiary wastewater treatment facility that serves the cities of Reno and Sparks, Nev. The effluent from TMWRF is discharged into the Truckee River which flows to Pyramid Lake—a very sensitive ecosystem and habitat for endangered species. Reverse osmosis (RO) and nanofiltration (NF), in conjunction with ultrafiltration (UF) pretreatment, were evaluated for total dissolved solids (TDS) and nutrient removal from the effluent of TMWRF at bench and pilot scale. Results from short-term pilot-scale tests showed that RO and NF membrane processes can successfully remove both TDS and nutrients from the effluent when paired with coagulation-enhanced UF pretreatment. NF membranes were able to achieve the necessary removal while maintaining higher fluxes and lower specific power consumption.