Viability study of different reverse osmosis membranes for application in the tertiary treatment of wastes from the tanning industry

The tanning industry uses large quantities of water and produces a correspondingly large amount of wastewater with high levels of salts and organic materials. Before these wastewaters can be eliminated, they must be submitted to a suitable depuration treatment. However, conventional treatments such as those used for urban wastewater are not able to reduce the salt content sufficiently and new methods need to be studied in the light of new technologies. In this aspect, membrane technology is increasingly used as a separation technique in chemical and environmental engineering, including desalination, selective separation and wastewater treatment. In this paper, we describe a comparative study of six different reverse osmosis membranes, which were tested for their ability to reduce the salt content in the tertiary treatment after the elimination of chromium salts and organic matter of an effluent from a pilot plant for treating industrial wastewater from the tanning industry to reach the legal levels established for their safe disposal. The membranes were checked using a 3×10⁻³ m² flat cell, where the concentrated streams were recirculated to the feed reservoir.     

Mechanical analysis of hollow fiber membrane integrity in water reuse applications

In order to gain insight into membrane fiber failure (i.e., loss of integrity), properties of five hollow fiber membranes and four hollow fiber modules were evaluated. Specifically, membrane material, membrane symmetry, fiber modulus of elasticity, fiber diameter and thickness, module potting technique, module flow pattern (inside-out or outside-in), and coliform breakthrough were investigated. The approach combined evaluation of the above properties with mathematical modeling of structure-fluid interactions to comprehensively evaluate the properties most important for maintaining hollow fiber membrane integrity. Tensile strength testing revealed that the strongest fiber was an asymmetric polyacrylonitrile membrane fiber. The weakest fiber was a symmetric polyethylene membrane fiber. Pilot plant testing on the four membrane modules revealed that membrane symmetry may be a more important factor than potting technique for hollow fiber integrity. Results from the SEM and tensile testing were used as input to a finite element analysis model used to evaluate time-dependent structure-fluid interactions. It was found that additional stresses at the juncture of the potting material and the hollow fiber membranes exist. These stresses likely lead to the formation of fractures.     

Characteristics of membrane humidifiers for polymer electrolyte membrane fuel cells

Water management plays an important role in obtaining high performance from a polymer electrolyte membrane fuel cell (PEMFC). To reduce the volume and energy consumption of widely-used bubble humidifiers, membrane humidifiers were fabricated by using an ultrafiltration (UF) membrane and Nafion membranes. The performance of the membrane humidifiers was examined as a function of gas flow rate and operating temperature. A single cell was operated using the UF membrane humidifiers exhibiting almost the same performance with that employing bubble humidifiers.     

Corrosion-resistant lightweight metallic bipolar plates for PEM fuel cells

Corrosion resistant treated metal bipolar plates with higher rigidity and electrical conductivity than graphite were developed and tested for PEM fuel cell applications. Six replicas of single cells were used three of which were made of graphite composites bipolar plates and the other three of the treated metallic plates. A Membrane Electrode Assembly (MEA) with 5.55 cm² active electrode areas, 0.3 mg cm^–2 Pt loading and Nafion membrane 115 was fitted to each cell and operated under identical conditions. The experimental testing was conducted at room temperature (20 °C). The average value of the data obtained for the three graphite cells was plotted. Similarly, the average value of the data obtained for the three treated metal cells was plotted on the same graph for comparison. Generally, the treated metal bipolar plate provided at least 12% saving in hydrogen consumption in comparison to graphite. This is attributed to the lower bulk and surface contact resistance of the metal used in this study in relation to graphite. The results of lifetime testing, conducted at room temperature under variable loading showed no indication of power degradation due to metal corrosion for at least 1500 hours.     

吸收浓度对玻璃态膜中气体吸收过程影响的研究

通过气体在玻璃态高分子膜中的吸收过程分析,认为在膜中气体分子与膜之间的相互作用将影响吸收等温线。假设气体在膜中的溶解过程类似于在溶液中的溶解过程,推导得出了普遍化双方式吸收模型。该模型中考虑了气体吸收浓度对气体在玻璃态膜中吸收过程的影响,几乎能够描述各种吸收过程。     

UiO-66/PES混合基质超滤膜的制备及性能

以聚醚砜(PES)为主要膜材料、溶剂热法合成UiO-66并掺入铸膜液中,通过非溶剂相转化法(NIPS)制备了混合基质超滤膜.利用X射线衍射仪(XRD)、傅里叶红外光谱(FTIR)、扫描电镜(SEM)、接触角测量仪及原子力显微镜(AFM)对制备的UiO-66和混合基质膜进行表征.重点考察了UiO-66添加量对膜表面形貌、...     

The Use of Reverse Osmosis in the Removal of PAHs from Municipal Landfill Leachate

Polycyclic aromatic hydrocarbons (PAHs) are relatively well-known organic pollutants and due to their carcinogenic and mutagenic properties their presence in the environment still attracts a lot of attention.

According to literature reports and own research, PAHs presence in wastewaters is common. It was confirmed that PAHs are the components of municipal landfill leachate. Membrane techniques are one of the most interesting ways of removing PAHs from leachate.

The purpose of this article is to monitor PAHs concentration changes during the membrane (reverse osmosis - RO) leachate treatment processes. In the first stage of testing leachates were filtrated on the sand bed (pre-filtration). After the pre-filtration they were directed to the membrane module for the main filtration.

Sixteen PAHs listed by EPA were analyzed. The results with information on PAHs concentration in leachate samples were presented using HPLC with fluorescence detection (FLD). The changes in PAHs concentration were determined in leachate samples before and after pre-filtration as well as after RO. The decrease of PAHs concentration in the samples was observed after these processes. The total concentration of 16 PAHs in raw municipal landfill leachates amounted to 23.64–26.95 μg/L. The research confirmed the high efficiency in removal of PAHs while using a reverse osmosis (59–72%). Including the pre-filtration, the overall level of removed PAHs reached 81–86%. The average PAHs concentration after pre-filtration and RO was in the 4.46–4.99 μg/L range. The municipal landfill leachate with a high concentration of PAHs should be cleaned before it is discharged into the environment.     

Recent advances in nanofiltration,reverse osmosis membranes and their applications in biomedical separation field

In the face of human society’s great requirements for health industry, and the much stricter safety and quality standards in the biomedical industry, the demand for advanced membrane separation technologies continues to rapidly grow in the world. Nanofiltration(NF) and reverse osmosis(RO) as the highefficient, low energy consumption, and environmental friendly membrane separation techniques, show great promise in the application of biomedical separation field. The chemical compositions, microstr...     

Microfabrication of vacuum-sealed cavities with nanocrystalline and ultrananocrystalline diamond membranes and their characteristics

Vacuum-sealed cavities featuring diamond membranes are fabricated using plasma-activated direct bonding technology. A chemical mechanical polished (CMP) silicon dioxide interlayer, deposited on diamond with a high temperature oxide (HTO) process at 850 °C in a low pressure chemical vapor deposition (LPCVD) furnace, is employed for successful direct bonding and vacuum cavity formation. The circular cavities are defined on the thermally grown oxide of the phosphorus-doped Si wafer (4-in, < 100>, 1.2 Ω/sq) using reactive ion etching (RIE). The same microfabrication steps are applied for low residual stress (i.e. < 50 MPa) nanocrystalline (NCD) and ultrananocrystalline (UNCD) diamonds to determine and compare membrane characteristics. For both diamond types, successful microfabrication of membranes is demonstrated using the optimized process flow. Profilometer measurements of membrane deflection are compared with finite element modeling (FEM), and indicate a Young's modulus of 1000 GPa for NCD and 850 GPa for UNCD. Furthermore, FEM analysis suggests the residual stress of UNCD membrane is approximately 100 MPa tensile, whereas NCD one does not show any significant residual stress (< 50 MPa). Our results show that NCD is a more promising choice than UNCD as a membrane material for electromechanical transducers.     

Separation of glycerol from FAME using ceramic membranes

International standards (e.g., ASTM D6751 and EN14214) limit the presence of free glycerol in biodiesel. The traditional water wash method for removing glycerol from crude fatty acid methyl esters (FAME) obtained in the production of biodiesel results in waste waters that cannot be readily discharged. To circumvent the water wash purification method, a membrane separation system using ceramic membranes was designed, constructed and tested for the removal of glycerol from crude FAME from a biodiesel production process. Ceramic membranes in the ultrafiltration (0.05 μm) and microfiltration (0.2 μm) ranges were tested at three different operating temperatures: 0, 5 and 25 °C. All runs separated glycerol from the crude FAME. International standards for glycerol content in biodiesel were met after 3 h when utilizing the ultrafiltration membrane setup at 25 °C with a concentration factor greater than 1.6.