Ceramic-Based Composite Membrane with a Porous Network Surface Featuring a Highly Stable Flux for Drinking Water Purification

Application of coal fly ash based ceramic membranes in wastewater treatment: A sustainable alternative to commercial materials

The continued increase in the global population has resulted in increased water demand for domestic, agricultural, and industrial purposes. These activities have led to the generation of high volumes of wastewater, which has an impact on water quality. Consequently, more practical solutions are needed to improve the current wastewater treatment systems. The use of improved ceramic membranes for wastewater treatment holds significant prospects for advancement in water treatment and sanitation. Hence, different studies have employed ceramic membranes in wastewater treatment and the search for low-cost and environmentally friendly starting materials has continued to engender research interests. This review focuses on the application of coal fly ash in membrane technology for wastewater treatment. The processes of membrane fabrication and the various limitations of the material. Several factors that influence the properties and performance of coal fly ash ceramic membranes in wastewater treatment are also presented. Some possible solutions to the limitations are also proposed, while cost analysis of coal fly ash-based membranes is explored to evaluate its potential for large-scale applications.

Ultra-Stable Inorganic Mesoporous Membranes for Water Purification

Thin, supported inorganic mesoporous membranes are used for the removal of salts, small molecules (PFAS, dyes, and polyanions) and particulate species (oil droplets) from aqueous sources with high flux and selectivity. Nanofiltration membranes can reject simple salts with 80-100% selectivity through a space charge mechanism. Rejection by size selectivity can be near 100% since the membranes can have a very narrow size distribution. Mesoporous membranes have received particular interest due to their (potential) stability under operational conditions and during defouling operations. More recently, membranes with extreme stability became interesting with the advent of in situ fouling mitigation by means of ultrasound emitted from within the membrane structure. For this reason, we explored the stability of available and new membranes with accelerated lifetime tests in aqueous solutions at various temperatures and pH values. Of the available ceria, titania, and magnetite membranes, none were actually stable under all test conditions. In earlier work, it was established that mesoporous alumina membranes have very poor stability. A new nanofiltration membrane was made of cubic zirconia membranes that exhibited near-perfect stability. A new ultrafiltration membrane was made of amorphous silica that was fully stable in ultrapure water at 80 °C. This work provides details of membrane synthesis, stability characterization and data and their interpretation.

Bio-Based Ceramic Membranes for Bacteria Removal from Water

Bio-based ceramic membranes were elaborated from kaolinite clays, coconut husks and eggshells to retain E. coli bacteria present in water intended for human consumption. Their characterization and removal performances are investigated in this work. These bio-ceramic membranes were obtained by heating the formulation containing 75% clay, 15% coconut husk and 10% eggshell at 900 °C or 1000 °C, at different temperature rates, to give S1, S2 and S3 materials. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), mercury porosimetry and scanning electron microscopy (SEM) were used to characterize these membranes. Water flux density, bacterial removal and biofouling were also assessed. Water flux density was shown to depend on material porosity. Bacteria retention was 90% (with 1 log-removal) for S1, 80% (with 0.7 log-removal) for S2 and 100% (with 3.3 log-removal) for S3. Membranes S1 and S2 presented reversible biofouling, while no fouling was evidenced for S3 in the tested conditions. This work shows that the best bio-ceramic membrane in terms of bacterial removal and flux density was S3. Its water flux density was 2123 ± 72 L/h/m² at an initial pressure of 0.2 bar. This material is particularly interesting because its production protocol is quite simple, fast and without the addition of chemical additives. Moreover, it can be used to efficiently remove bacteria from drinking water.

New Low-Cost Ceramic Microfiltration Membranes for Bacteria Removal

Safe water provision in low-income countries is constrained by limited financial resources, and the problem is worsened during natural disasters. Thus, there is a need to develop efficient low-cost technologies for point-of-use water treatment. This work reports on the development of new ceramic microfiltration membranes made from mixtures of inexpensive raw materials available locally (kaolin, bentonite and limestone) and their efficiency in rejecting bacteria such as Escherichia coli and Staphylococcus aureus. Thermogravimetric analysis, differential scanning calorimetry, Fourier-transform infrared spectroscopy, X-ray diffraction, mercury intrusion porosimetry, flexural strength and water uptake were used to characterize the raw materials and membranes. The addition of limestone in the membrane fabrication increased the pore size, the porosity and, thus, the permeability of the membranes but at the expense of the rejection performance. Among the different compositions studied, the membrane made of 83% kaolin, 10% bentonite and 7% limestone showed the best performance compromise with water permeability of 566 L·h⁻¹·m⁻²·bar⁻¹ and 100% rejection of both Escherichia coli and Staphylococcus aureus. These new low-cost microfiltration membranes are expected to have potential applications in water treatment and household applications.

Process intensification through waste fly ash conversion and application as ceramic membranes: A review

Improper disposal of huge quantities of fly ash generated by thermal power plants and few other industries contributes to both air and water pollution, and therefore, recent advancements in research are focused toward utilizing this waste material in fabricating useful membranes. This article presents an overview of various methods used to fabricate fly ash-based membranes and critical parameters affecting the same. Fly ash-based membranes also act as the support for fabricating composite membranes and therefore, different means of coating the support membranes are discussed in this paper. Among various methods of membrane fabrication, extrusion method can be considered for bulk production of membranes, which is a pre-requisite for industrial implementation. The article also throws light on a wide range of wastewater that have been successfully treated using these fly ash-based ceramic membranes. However, the use of these membranes should be avoided in acidic solutions as it may cause leaching of heavy metals present in fly ash, causing health hazards. Most of these membranes function on the basis of size exclusion principle, whereas membranes with charge-based separation are also well known. Both of these types of membranes are discussed in this work. Utilization of fly ash-based membranes in separation processes not only reduce the cost associated with the process, but will also intensify the process through various other means such as reduced energy consumption, environmental safety and so on. Thus, the main focus of this review is to present the readers with development and important future directions in this research topic.

Vertically Aligned Carbon Nanotube Membranes: Water Purification and Beyond

Vertically aligned carbon nanotube (VACNT) membranes have attracted significant attention for water purification owing to their ultra-high water permeability and antibacterial properties. In this paper, we critically review the recent progresses in the synthesis of VACNT arrays and fabrication of VACNT membrane methods, with particular emphasis on improving water permeability and anti-biofouling properties. Furthermore, potential applications of VACNT membranes other than water purification (e.g., conductive membranes, electrodes in proton exchange membrane fuel cells, and solar electricity–water generators) have been introduced. Finally, future outlooks are provided to overcome the limitations of commercialization and desalination currently faced by VACNT membranes. This review will be useful to researchers in the broader scientific community as it discusses current and new trends regarding the development of VACNT membranes as well as their potential applications.

Facile fabrication of a low-cost and environmentally friendly inorganic-organic composite membrane for aquatic dye removal

This study reports a new inorganic-organic composite membrane fabricated by an electrostatic self-assembling method. The low-cost and eco-friendly porous geopolymer (PG) was chosen as a support, on which chitosan (CS), a "green" biomaterial, was used to form an active layer. With optimum dosage of CS (2.0 mL of 1.0% CS solution), the obtained CS/PG membrane exhibited a high porosity of 50.97% with an average pore diameter of 13.93 nm as well as a high water flux of 1663.82 ± 22.46 L/m²·h·bar. The effects of initial concentration, pH, flow rate and temperature of the feed solution on crystal violet (CV) removal by the CS/PG were evaluated in a continuous mode. The results indicated ~95% CV could be removed from water during continuous treating of 14 h. The effectiveness in CV removal by the CS/PG membrane was attributed to the synergistic effect of rejection and adsorption. Furthermore, the composite membrane could be easily regenerated for prolonged use. Overall, this work opens a new possibility of building cost-saving and eco-friendly composite membranes for practical applications in water purification.

Materials and Applications for Low-Cost Ceramic Membranes

In water treatment applications, the use of ceramic membranes is associated with numerous advantages relative to polymer-based filtration systems. High-temperature stability, fouling resistance, and low maintenance requirements contribute to lower lifecycle costs in such systems. However, the high production costs of most commercially available ceramic membranes, stemming from raw materials and processing, are uneconomical for such systems in most water treatment applications. For this reason, there is a growing demand for new ceramic membranes based on low-cost raw materials and processes. The use of unrefined mineral feedstocks, clays, cement, sands, and ash as the basis for the fabrication of ceramic membranes offers a promising pathway towards the obtainment of effective filtration systems that can be economically implemented in large volumes. The design of effective ceramic filtration membranes based on low-cost raw materials and energy-efficient processes requires a balance of pore structure, mass flow, and robustness, all of which are highly dependent on the composition of materials used, the inclusion of various pore-forming and binding additives, and the thermal treatments to which membranes are subjected. In this review, we present recent developments in materials and processes for the fabrication of low-cost membranes from unrefined raw materials, including clays, zeolites, apatite, waste products, including fly ash and rice husk ash, and cement. We examine multiple aspects of materials design and address the challenges relating to their further development.