Cleaning of wastewater for the environment is an emerging issue for the living organism. The separation of oily wastewater, especially emulsified mixtures, is quite challenged due to a large amount of wastewater produced in daily life. In this review, the membrane technology for oily wastewater treatment is presented. In the first part, the global membrane market, the oil spill accidents and their results are discussed. In the second and third parts, the source of oily wastewater and conventional treatment methods are represented. Among all methods, membrane technology is considered the most efficient method in terms of high separation performance and easy to operation process. In the fourth part, we provide an overview of membrane technology, fouling problem, and how to improve the self-cleaning surface using functional groups for effectively treating oily wastewater. The recent development of surface-modified membranes for oily wastewater separation is investigated. It is believed that this review will promote understanding of membrane technology and the development of surface modification strategies for anti-fouling membranes.
Preparing easily scaled up, cost-effective, and recyclable membranes for separation technology is challenging. In the present study, a unique and new type of modified polyvinylidene fluoride (PVDF) nanofibrous membrane was prepared for the separation of oil–water emulsions. Surface modification was done in two steps. In the first step, dehydrofluorination of PVDF membranes was done using an alkaline solution. After the first step, oil removal and permeability of the membranes were dramatically improved. In the second step, TiO2 nanoparticles were grafted onto the surface of the membranes. After adding TiO2 nanoparticles, membranes exhibited outstanding anti-fouling and self-cleaning performance. The as-prepared membranes can be of great use in new green separation technology and have great potential to deal with the separation of oil–water emulsions in the near future.
In order to protect the environment, it is important that oily industrial wastewater is degreased before discharging. Membrane filtration is generally preferred for separation of oily wastewater as it does not require any specialised chemical knowledge, and also for its ease of processing, energy efficiency and low maintenance costs. In the present work, hybrid polyacrylonitrile (PAN) nanofibrous membranes were developed for oily wastewater filtration. Membrane surface modification changed nitrile groups on the surface into carboxylic groups, which improve membrane wettability. Subsequently, TiO2 nanoparticles were grafted onto the modified membranes to increase flux and permeability. Following alkaline treatment (NaOH, KOH) of the hydrolysed PAN nanofibres, membrane water permeability increased two- to eight-fold, while TiO2 grafted membrane permeability increase two- to thirteen-fold, compared to unmodified membranes. TiO2 grafted membranes also displayed amphiphilic properties and a decrease in water contact angle from 78.86° to 0°. Our results indicate that modified PAN nanofibrous membranes represent a promising alternative for oily wastewater filtration.
Around 1.2 billion people have limited access to drinkable water and millions succumb every year to sicknesses caused due to the consumption of impure water or lack of water. In the coming years, this problem will only progress at alarming rates due to the aggressive growth of population, urbanization and droughts. It is essential to investigate new approaches for water treatment with low energy costs and economic benefits. The biggest problem in membrane filtrations is fouling, which causes membrane pore blockages and creates a cake layer on the membrane surface. The aim of the project is to obtain nanofibrous membranes that will have high fouling resistance and antibacterial effects. Nanoparticles of Ag, ZnO, TiO2 and CuO are known for their antibacterial properties. In order to attach nanoparticles to the membrane surface, appropriate functional groups are required. The first step of the project involves the attachment of functional groups capable of binding nanoparticles to the surface of the nanofiber membrane. For this alkaline surface modification using NaOH, KOH, DETA under different conditions was performed. After modification, changes in hydrophilicity and structure of membranes, pore size and appearance of nanofibers were checked. Defluorination reaction conditions with NaOH and KOH proved to be insufficient to obtain the desired functional groups on the membrane surface. In the case of the reaction with DETA, amine groups were obtained, which will be used in the next step to attach the nanoparticles.
Water demand is steadily increasing, and usable water supply is constantly decreasing. It is urgent to find a cheap and efficient way to recycle water. Currently, membrane technologies are getting promising results, but some factors drastically reduce their effectiveness. In membrane filtration, biofouling is one of the most limiting factors, reducing filtration efficiency. In this work, the micro- and nanofibres-composed membranes were modified with diethylenetriamine (DETA), and silver nanoparticles were attached to a modified surface to minimize biofouling risk during filtration. Different conditions were tested for reaction with DETA and attachment of nanoparticles. Antimicrobial tests were performed, and the leaching of nanoparticles over time was checked. The modified membranes (Nadir® MV020T and PA PVDF) containing silver nanoparticles ranging in size from 20 to 50 nm showed antibacterial properties against Escherichia coli in the form of 3–4 mm inhibitory zones. The percentage of released AgNPs was 0.47% and 2.12% for Nadir® MV020T and PA PVDF membrane after 21 days, respectively. Polyvinylpyrrolidone was used to increase the stability of the nanoparticles, and the results were compared.
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