Types Of Membrane Fouling Research Articles

Effect of polymaleic acid and microwave radiations on reverse osmosis membrane's performance and properties: A response surface methodology approach

Polymaleic acid was tested for its ability to control inorganic fouling in reverse osmosis (RO) system for the first time as a membrane surface modifier. Using the design of experiments (DoE) based on the response surface methodological (RSM) approach, the effect of polymaleic acid concentration and microwave radiation time duration was studied on the membrane permeation properties. Considering the objective of achieving maximum water permeance and salt rejection properties, the conditions of polymerization were optimized using RSM and experimentally validated in the lab. At the optimum conditions of 10 mg·L−1 polymaleic acid, and 27 s radiation time, the pure water permeance and salt rejection were 3.05 L·m−2·h−1·bar−1, and 97.8 %, respectively. The optimized membrane was characterized through microscopic and spectroscopic techniques. When tested for its performance under inorganic fouling conditions, the modified membrane demonstrated a negligible decline in permeate flux for 6 h, and no formation of calcium sulfate precipitates on the membrane surface. This research aims to promote the development, optimization, and application of dual-functional RO membranes that can control different types of membrane fouling.

Investigating the effect of polymer-modified graphene oxide coating on RO membrane fouling

The development of novel reverse osmosis (RO) membranes resistant to multiple types of fouling is a need to secure clean water production and meet rising water demands. In this paper, the RO membrane surface-functionalized with antibacterial graphene oxide (GO) and antiscalant maleic acid was prepared and tested. The polymerization of maleic acid on the GO functionalized RO membrane was achieved using microwave radiation. The membrane surface characterization showed a decrease in membrane surface roughness from 74.7 nm to 69.0 nm and an increase in membrane hydrophilicity as the contact angle decreased from 41.7 ± 4.50 to 22.0 ± 1.10. The modified membrane was tested against inorganic scaling and biofouling, and the results demonstrated that the modified membrane has improved resistance to multiple fouling types as compared to the unmodified RO membrane. When tested in the presence of calcium sulfate scaling solution (inorganic fouling), the normalized permeate flux was found to be stable at 0.91 and 0.95 for 0.01 and 0.02 wt% maleic acid-modified RO membranes, respectively. Moreover, the modified membranes also demonstrated bacteriostasis rates of 96.1 %–97.1 % showing their anti-bacterial characteristics. Both types of membrane fouling (inorganic and biofouling) were also studied simultaneously, and the results showed that the RO membranes with dual capabilities can inhibit both mineral formation and biofilm growth concurrently.

Membrane Distillation: Recent Configurations, Membrane Surface Engineering, and Applications.

Membrane distillation (MD) is a developing membrane separation technology for water treatment that involves a vapor transport driven by the vapor pressure gradient across the hydrophobic membrane. MD has gained wide attention in the last decade for various separation applications, including the separation of salts, toxic heavy metals, oil, and organic compounds from aqueous solutions. Compared with other conventional separation technologies such as reverse osmosis, nanofiltration, or thermal distillation, MD is very attractive due to mild operating conditions such as low temperature and atmospheric pressure, and 100% theoretical salt rejection. In this review, membrane distillation’s principles, recent MD configurations with their advantages and limitations, membrane materials, fabrication of membranes, and their surface engineering for enhanced hydrophobicity are reviewed. Moreover, different types of membrane fouling and their control methods are discussed. The various applications of standalone MD and hybrid MD configurations reported in the literature are detailed. Furthermore, studies on the MD-based pilot plants installed around the world are covered. The review also highlights challenges in MD performance and future directions.

Functionalization of reverse osmosis membrane with graphene oxide and polyacrylic acid to control biofouling and mineral scaling

The polyamide reverse osmosis (RO) membrane was modified with graphene oxide (GO), followed by polymerization of acrylic acid (used as an antiscalant) for the reduction of both biofouling and mineral scaling. After functionalization, the water contact angle reduced from 41.7 ± 4.5° for unmodified RO membrane to 24.4 ± 1.3° for the modified RO membranes, which showed that membrane hydrophilicity was significantly enhanced, in addition to the improvement in surface smoothness. The modified membranes were tested for their anti-scaling and anti-biofouling characteristics. When the mineral scaling test was performed using CaSO4 solution as feedwater, the permeate flux was reduced by only 3% as compared to the unmodified RO membrane which encountered up to 22% decline in flux by the end of the experiment. After the scaling test, the membrane surface was characterized by Scanning electron microscopy – energy-dispersive X-ray spectroscopy, Fourier transform infrared, and X-ray diffraction techniques. The results showed that the unmodified RO membrane was fully covered with gypsum precipitates. Whereas, the precipitates were detected only at the highly saturated zones of the water channel i.e. towards the exit of water flow. Additionally, the anti-bacterial test was performed through bacteriostasis rate determination, which showed that the modified membranes inhibited the growth of nearly 95% of the bacterial cells. Further experiments were also performed to investigate the inhibition of both scaling and biofouling by modified RO membranes. Thus, it was found that the polymer-modified GO coated RO membranes were able to diminish both gypsum scaling and biofilm formation demonstrating their potential to control different types of membrane fouling.

Effects of organic, biological and colloidal fouling on the removal of pharmaceuticals and personal care products by nanofiltration and reverse osmosis membranes

The impact of different foulant composition and pHs on the removal of pharmaceutical and personal care products (PPCPs) by nanofiltration (NF270 and NF90) and reverse osmosis (XLE) membranes was investigated in this study. Humic acid (HA), alginate (SA) and silica (Si) were used for the formation of organic, biological and colloidal fouling, respectively, and were further mixed for the formation of composite fouling on membrane surfaces. The results show that significant flux decline was observed with decreasing pH and all kinds of foulant composition for the three membranes, which was contributed mostly by irreversible fouling, especially for the tight XLE. Moreover, the trends of flux decline and particle size of composite foulants at different pHs were dominant by HA for all membranes, implying that the control of organic matrix in water before reaching NF/RO process is crucial to the performance of membrane filtration. On the other hand, all types of membrane fouling caused the decrease of PPCP rejection by NF270, especially for the hydrophilic-ionized and hydrophobic-ionized compounds at low pHs because of the shield of dominant electrostatic repulsion mechanism between PPCPs and membrane surface, causing the cake-enhanced concentration polarization phenomenon. The results were verified by dense and thick cake layers observed using scanning electron microscopy, the corresponding change of contact angles, and high adsorption amount of very hydrophobic triclosan on the active layer of NF270. However, steric hindrance and electrostatic repulsion worked synergistically for the increasing PPCP rejection by NF90 with increasing pH and membrane fouling, while steric hindrance dominates PPCP rejection by XLE. Therefore, one order less triclosan adsorption happened on membrane surface and the fouling layer of NF90 and XLE. The fouling mechanisms were illustrated using the modified Hermia model as gel layer formation for the loose NF270, intermediate blocking for NF90 and complete blocking for XLE.

A novel in situ membrane cleaning method using periodic electrolysis

Membrane fouling is the major problem during the practical application of membrane separation processes in industry and water treatment. Therefore a search for novel efficient methods of membrane cleaning is currently of crucial importance for membrane-based technologies. The paper describes a new method of membrane cleaning, which is based on periodic electrolysis using a novel electrically conductive membrane to remove/prevent membrane fouling. The membrane consists of a thin electrically conductive layer of multi-walled carbon nanotubes (MWCNTs) deposited on the membrane׳s surface. The deposited MWCNTs allow the membrane to function as a cathode in an electrochemical system that includes the electrically conductive membrane, the salt water as an electrolyte and a stainless steel counter anode. The efficiency of the cleaning procedure in the flux recovery has been proved with typical bio- and inorganic membrane foulants such as CaCO3 and yeast suspensions. The cleaning mechanism during the electrolysis process is explained by the evolution of gases forming micro-bubbles at the membrane surface which remove the foulant material out from the membrane. The proposed method enables in situ membrane self-cleaning, thus providing a non-destructive, continuous and renewable approach for the mitigation of the different types of membrane fouling.

Fouling behaviors of polybenzimidazole (PBI)–polyhedral oligomeric silsesquioxane (POSS)/polyacrylonitrile (PAN) hollow fiber membranes for engineering osmosis processes

This paper investigated the individual effects of reverse salt flux and permeate flux on fouling behaviors of as-spun and annealed polybenzimidazole (PBI)–polyhedral oligomeric silsesquioxane (POSS)/polyacrylonitrile (PAN) hollow fiber membranes under forward osmosis (FO) and pressure retarded osmosis (PRO) processes. Two types of membrane fouling had been studied; namely, inorganic fouling (CaSO4·2H2O gypsum scaling) during FO operations and organic fouling (sodium alginate fouling) during PRO operations. It is found that gypsum scaling on the membrane surface may be inhibited and even eliminated with an increase in reverse MgCl2 flux due to competitive formations of MgSO4° and CaSO4·2H2O. In contrast, the increase of reverse NaCl flux exhibits a slight enhancement on alginate fouling in both FO and PRO processes. Comparing to the reverse salt flux, the permeate flux always plays a dominant role in fouling. Therefore, lesser fouling has been observed on the membrane surface under the pressurized PRO process than FO process because the reduced initial flux mitigates the fouling phenomena more significantly than the enhancement caused by an increase in reverse NaCl flux.

A review of membrane fouling in municipal secondary effluent reclamation

Reclamation of municipal secondary effluent for non-potable purposes is considered vital in alleviating the demand for existing limited water supplies while helping to protect remaining water sources from being polluted. In recent decades, reverse osmosis and nanofiltration membrane technologies have become increasingly attractive for reclamation of municipal secondary effluent because they are highly efficient, easy to operate, and economical. However, membrane fouling is a major obstacle in the development of membrane technology in municipal secondary effluent reclamation. This paper reviews three types of membrane fouling in municipal secondary effluent reclamation, namely, effluent organic matter (EfOM) membrane fouling, microbial membrane fouling, and inorganic membrane fouling, as well as their correlation. Membrane fouling by EfOM and microbes are found to be severe, and they are significantly correlated. Most previous studies conducted laboratory-scale experiments of membrane fouling with model organic matters and bacteria, but these model organic matters and bacteria might still be unrepresentative. More studies on membrane fouling in municipal secondary effluent reclamation with actual wastewater are essential.

Performance of Membrane Bio-Reactor Equipped with Air-Sparged Side-Stream Tubular Membrane: Treatment Efficiency and Membrane Fouling

We conducted a high-load operation of a baffled bio-reactor equipped with air-sparged side-stream tubular membrane modules for treating actual municipal wastewater at two different periods (high- and low-temperature). Although nitrogen removal efficiency slightly decreased at the low-temperature period, this baffled bio-reactor showed excellent nitrogen and phosphorus removal efficiencies. We also investigated the developments of both physically reversible and irreversible fouling during operation with two-phase flow (mixed-liquor and gas) at various gas velocities and the mixed-liquor velocity was fixed at 0.50 m/s. The membrane flux was fixed at 80 L/m2/hour throughout the experiments. Regardless of the difference in temperature, the trends in the development of these two types of membrane fouling caused by the difference in gas velocity were similar. For physically reversible fouling, an optimum gas velocity, in which the development of this type of fouling was minimized, was found to be around 0.42 m/s (corresponding void fraction was 0.45). A further increase in gas velocity resulted in more reversible fouling. On the other hand, the degree of physically irreversible fouling decreased as gas velocity increased. The results obtained in this study indicated the effect of gas velocity on fouling control differs depending on the type of membrane fouling.

Polysulfone ultrafiltration membranes impregnated with silver nanoparticles show improved biofouling resistance and virus removal

Biofouling and virus penetration are two significant obstacles in water treatment membrane filtration. Biofouling reduces membrane permeability, increases energy costs, and decreases the lifetime of membranes. In order to effectively remove viruses, nanofiltration or reverse osmosis (both high energy filtration schemes) must be used. Thus, there is an urgent demand for low pressure membranes with anti-biofouling and antiviral properties. The antibacterial properties of silver are well known, and silver nanoparticles (nAg) are now incorporated into a wide variety of consumer products for microbial control. In this study, nAg incorporated into polysulfone ultrafiltration membranes (nAg–PSf) exhibited antimicrobial properties towards a variety of bacteria, including Escherichia coli K12 and Pseudomonas mendocina KR1, and the MS2 bacteriophage. Nanosilver incorporation also increased membrane hydrophilicity, reducing the potential for other types of membrane fouling. XPS analysis indicated a significant loss of silver from the membrane surface after a relatively short filtration period (0.4 L/cm 2) even though ICP analysis of digested membrane material showed that 90% of the added silver remained in the membrane. This silver loss resulted in a significant loss of antibacterial and antiviral activity. Thus, successful fabrication of nAg-impregnated membranes needs to allow for the release of sufficient silver ions for microbial control while preventing a rapid depletion of silver.