The impact of PET microplastic fibres on PVDF ultrafiltration performance - A short-term assessment of MP fouling in simple and complex matrices

Hydraulic and chemical cleaning efficiency for the release of microplastics retained during coagulation/flocculation-ultrafiltration

Microplastics (MPs) are ubiquitous in global drinking water sources (lakes, rivers), with reported concentrations ranging from 0.5 to >7,500 particles/L. Ultrafiltration (UF), widely applied in drinking water treatment, is anticipated to represent an effective barrier to MPs due to its pore size (0.01-0.1 µm), which can retain MPs of potential health concern. To-date limited studies have reported that MPs may contribute to UF fouling, albeit when considering concentrations up to 10 orders of magnitude higher than those typically observed in source waters. The present study evaluated the retention of MPs by UF membranes when incorporating coagulation/flocculation pre-treatment, as well as their release during hydraulic and chemical cleaning. Polyethylene (PE) fragments, representing a range of environmentally relevant sizes (1-50 µm) and concentrations (907 ± 293 particles/L), were spiked into untreated lake waters prior to coagulation/flocculation-UF. Results suggest that in the absence of coagulant (alum) addition, only 50% of MPs retained during UF permeation were subsequently released during hydraulic cleaning. The release of MPs during hydraulic cleaning decreased (<20%) at medium and high (8 mg/L, 15 mg/L) alum dosages when compared to the absence of coagulant addition. Chemical cleaning with sodium hypochlorite (500 mg/L) was only capable of releasing 20% to 60% of retained MPs. Both hydraulic and chemical cleaning were less effective for the release of MPs when compared to reversible fouling resistance, organic matter, and aluminum. As such, future research is required to determine if the accumulation of MPs leads to increased UF fouling over extended operating periods, in addition cleaning practices which specifically target MPs should be further examined. Low and medium alum dosages (2 mg/L, 8 mg/L) were observed to increase the release of retained MPs during chemical cleaning, suggesting that incorporation of coagulation pre-treatment is useful to increase the release of MPs and minimize potential long-term accumulation on membranes.

Pressure-Driven Membrane Processes for Removing Microplastics

The intense consumption of polymeric materials combined with poor waste management results in the dissemination of their fragments in the environment as micro- and nanoplastics. They are easily dispersed in stormwater, wastewater, and landfill leachate and carried towards rivers, lakes, and oceans, causing their contamination. In aqueous matrices, the use of membrane separation processes has stood out for the efficiency of removing these particulate contaminants, achieving removals of up to 100%. For this review article, we researched the removal of microplastics and nanoplastics by membrane processes whose driving force is the pressure gradient. The analysis focuses on the challenges found in the operation of microfiltration, ultrafiltration, nanofiltration, and reverse-osmosis systems, as well as on the innovations applied to the membranes, with comparisons of treatment systems and the peculiarities of each system and each aqueous matrix. We also point out weaknesses and opportunities for future studies so that these techniques, known to be capable of removing many other contaminants of emerging concern, can subsequently be widely applied in the removal of micro- and nanoplastics.

Dry-spun carbon nanotube ultrafiltration membranes tailored by anti-viral metal oxide coatings for human coronavirus 229E capture in water

Although waterborne virus removal may be achieved using separation membrane technologies, such technologies remain largely inefficient at generating virus-free effluents due to the lack of anti-viral reactivity of conventional membrane materials required to deactivating viruses. Here, a stepwise approach towards simultaneous filtration and disinfection of Human Coronavirus 229E (HCoV-229E) in water effluents, is proposed by engineering dry-spun ultrafiltration carbon nanotube (CNT) membranes, coated with anti-viral SnO2 thin films via atomic layer deposition. The thickness and pore size of the engineered CNT membranes were fine-tuned by varying spinnable CNT sheets and their relative orientations on carbon nanofibre (CNF) porous supports to reach thicknesses less than 1 µm and pore size around 28 nm. The nanoscale SnO2 coatings were found to further reduce the pore size down to ∼21 nm and provide more functional groups on the membrane surface to capture the viruses via size exclusion and electrostatic attractions. The synthesized CNT and SnO2 coated CNT membranes were shown to attain a viral removal efficiency above 6.7 log10 against HCoV-229E virus with fast water permeance up to ∼4 × 103 and 3.5 × 103 L.m-2.h-1.bar-1, respectively. Such high performance was achieved by increasing the dry-spun CNT sheets up to 60 layers, orienting successive 30 CNT layers at 45°, and coating 40 nm SnO2 on the synthesized membranes. The current study provides an efficient scalable fabrication scheme to engineer flexible ultrafiltration CNT-based membranes for cost-effective filtration and inactivation of waterborne viruses to outperform the state-of-the-art ultrafiltration membranes.

Facile, green and scalable preparation of low-cost PET-PVDF felts for oil absorption and oil/water separation

3D felt materials with pore structures have the advantages of high absorption performance and recyclability in oily wastewater treatment and chemical leakage. However, most of them were fabricated using either toxic organic solvents or complicated procedures. Herein, we report a facile, green, and scalable route for the fabrication of 3D composite felts with large pore structures by sequentially stirring and heating polyethylene terephthalate (PET) fibers and polyvinylidene fluoride (PVDF). The resulting PET-PVDF felt exhibits high oil absorption capacity to a variety of oil and organic solvents with a maximum saturated absorption capacity of 32 g/g. Additionally, it can be used to separate oil/water mixtures with a separation efficiency of 99.9% and separation flux of 89570 L m^-2 h^-1. Moreover, this felt shows excellent mechanical durability and chemical stability under acid, base, salt solution, and other harsh environments. The current study provides a promising approach for large-scale industrial oily wastewater separation.

An assessment of the impact of structure and type of microplastics on ultrafiltration technology for microplastic remediation

Microplastic, which is of size less than 5 mm, is gaining a lot of attention as it has become a new arising contaminant because of its ecophysiology impact on the aquatic environment. These microplastics are found in freshwater or drinking water and are the major carriers of pollutants. Removal of this microplastic can be done through the primary treatment process, secondary treatment process, and tertiary treatment process. One approach for microplastic remediation is ultrafiltration technology, which involves passing water through a membrane with small pores to filter out the microplastics. However, the efficiency of this technology can be affected by the structure and type of microplastics present in the water. New strategies can be created to improve the technology and increase its efficacy in removing microplastics from water by knowing how various types and shapes of microplastics react during ultrafiltration. The filter-based technique, that is, ultrafiltration has achieved the best performance for the removal of microplastic. But with the ultrafiltration, too some microplastic that are of sizes less than of ultrafiltration membrane passes through the filter and enters the food chain. Accumulation of this microplastic on the membrane also leads to membrane fouling. Through this review article, we have assessed the impact of the structure, size, and type of MPs on ultrafiltration technology for microplastic remediation, with that how these factors affect the efficiency of the filtration process and challenges occur during filtration.