Novel floating photocatalysts based on polyurethane composite foams modified with silver/titanium dioxide/graphene ternary nanoparticles for the visible-light-mediated remediation of diesel-polluted surface water

Mechanisms and Strategies of Advanced Oxidation Processes for Membrane Fouling Control in MBRs: Membrane-Foulant Removal versus Mixed-Liquor Improvement

Membrane bioreactors (MBRs) are well-established and widely utilized technologies with substantial large-scale plants around the world for municipal and industrial wastewater treatment. Despite their widespread adoption, membrane fouling presents a significant impediment to the broader application of MBRs, necessitating ongoing research and development of effective antifouling strategies. As highly promising, efficient, and environmentally friendly chemical methods for water and wastewater treatment, advanced oxidation processes (AOPs) have demonstrated exceptional competence in the degradation of pollutants and inactivation of bacteria in aqueous environments, exhibiting considerable potential in controlling membrane fouling in MBRs through direct membrane foulant removal (MFR) and indirect mixed-liquor improvement (MLI). Recent proliferation of research on AOPs-based antifouling technologies has catalyzed revolutionary advancements in traditional antifouling methods in MBRs, shedding new light on antifouling mechanisms. To keep pace with the rapid evolution of MBRs, there is an urgent need for a comprehensive summary and discussion of the antifouling advances of AOPs in MBRs, particularly with a focus on understanding the realizing pathways of MFR and MLI. In this critical review, we emphasize the superiority and feasibility of implementing AOPs-based antifouling technologies in MBRs. Moreover, we systematically overview antifouling mechanisms and strategies, such as membrane modification and cleaning for MFR, as well as pretreatment and in-situ treatment for MLI, based on specific AOPs including electrochemical oxidation, photocatalysis, Fenton, and ozonation. Furthermore, we provide recommendations for selecting antifouling strategies (MFR or MLI) in MBRs, along with proposed regulatory measures for specific AOPs-based technologies according to the operational conditions and energy consumption of MBRs. Finally, we highlight future research prospects rooted in the existing application challenges of AOPs in MBRs, including low antifouling efficiency, elevated additional costs, production of metal sludge, and potential damage to polymeric membranes. The fundamental insights presented in this review aim to elevate research interest and ignite innovative thinking regarding the design, improvement, and deployment of AOPs-based antifouling approaches in MBRs, thereby advancing the extensive utilization of membrane-separation technology in the field of wastewater treatment.

Floating photocatalysts as promising materials for environmental detoxification and energy production: A review

The oxygenation process of the catalyst surface, the incident-light harvesting capability, and facile recycling of utilized photocatalysts play key role in the outstanding photocatalytic performances. The typical existing photocatalysts in powder form have many drawbacks, such as difficult separation from the treated water, insufficient surface oxygenation, poor active surface area, low incident-light harvesting ability, and secondary pollution of the environment. A great number of scientific works introduced novel and fresh ideas related to designing floating photocatalytic systems by immobilizing highly active photocatalysts onto a floatable substrate. Thanks to direct contact with the illuminated light and oxygen molecules in the interface of water/air, the photocatalytic performance is maximized through production of more reactive species, employed in the photocatalytic reactions. Furthermore, facile recovering of the utilized photocatalysts for next processes avoids secondary pollution as well as diminishes the process's price. This review highlights the performance of developed floating photocatalysts for diverse applications. Furthermore, different floating substrates and possible mechanisms in floating photocatalysts are briefly mentioned. In addition, several emerging self-floating photocatalytic systems are taken attention and discussed. Specially, coupling photo-thermal and photocatalytic effects seems to be a good strategy for introducing a new class of floating photocatalyst to utilize the free, abundant, and green sunlight energy for the aims of water desalination and purification. Despite of a large number of attempts about the floating photocatalysts, there are still plenty of rooms for more in-depth research to be carried out for attaining the required characteristics of the large scale utilizations of these materials.

"Needle" hidden in silk floss: Inactivation effect and mechanism of melamine sponge loaded bismuth oxide composite copper-metal organic framework (MS/Bi2O3@Cu-MOF) as floating photocatalyst on Microcystis aeruginosa

Photocatalytic technology showed significant potential for addressing the issue of cyanobacterial blooms resulting from eutrophication in bodies of water. However, the traditional powder materials were easy to agglomerate and settle, which led to the decrease of photocatalytic activity. The emergence of floating photocatalyst was important for the practical application of controlling harmful algal blooms. This study was based on the efficient powder photocatalyst bismuth oxide composite copper-metal organic framework (Bi2O3 @Cu-MOF), which was successfully loaded onto melamine sponge (MS) by sodium alginate immobilization to prepare a floating photocatalyst MS/Bi2O3 @Cu-MOF for the inactivation of Microcystis aeruginosa (M. aeruginosa) under visible light. When the capacity was 0.4 g (CA0.4), MS/Bi2O3 @Cu-MOF showed good photocatalytic activity, and the inactivation rate of M. aeruginosa reached 74.462% after 120 h. MS/Bi2O3 @Cu-MOF-CA0.4 showed a large specific surface area of 30.490 m2/g and an average pore size of 22.862 nm, belonging to mesoporous materials. After 120 h of treatment, the content of soluble protein in the MS/Bi2O3 @Cu-MOF-CA0.4 treatment group decreased to 0.365 mg/L, the content of chlorophyll a (chla) was 0.023 mg/L, the content of malondialdehyde (MDA) increased to 3.168 nmol/mgprot, and the contents of various antioxidant enzymes experienced drastic changes, first increasing and then decreasing. The photocatalytic process generated·OH and·O2-, which played key role in inactivating the algae cells. Additionally, the release of Cu2+ and adsorption of the material also contributed to the process.

Critical review on modified floating photocatalysts for emerging contaminants removal from landscape water: problems, methods and mechanism

Due to the disorderly discharge in modern production and daily life of people, emerging contaminants(ECs) began to appear in landscape water, and have become a key public concern. Because of the unique characteristics of landscape water, it is difficult to efficiently remove ECs either by natural purification or by traditional large-scale sewage treatment facilities. The ideal purification method is to remove them while maintaining a beautiful environment. Possessing the feature of low-density, floating photocatalysts could harvest sufficient light on the surface of the water for photocatalytic degradation, which may be an important supplement for ECs treatment in landscape water. This paper gave a review related to floating photocatalysts and proposed an idea of combining floating photocatalysts to construct bionic photocatalytic materials for contaminative landscape water treatment. Six types of common floating substrates and corresponding applications for floating photocatalysts were concluded in this paper, and the main problem leading to the low efficiency of photocatalysts and three corresponding three improvement strategies were discussed. Besides, the modification mechanisms of photocatalysts were discussed thoroughly. On this basis, the engineering application prospects of bionic photocatalytic materials were proposed to remove ECs in landscape water.

Bio-sorbent from castor oil polyurethane foam containing cellulose-halloysite nanocomposite for removal of manganese, nickel and cobalt ions from water

In order to mitigate the contamination of water with heavy metals, caused by mining dam failures in Brumadinho and Mariana in Brazil, eco-friendly bio-based castor oil polyurethane foams, containing a cellulose-halloysite green nanocomposite were prepared. Polyurethane foams containing none (PUF-0), 5%wt (PUF-5), and 10%wt (PUF-10) of the nanocomposite were obtained. The application of the material in aqueous media was verified through an investigation of the efficiency of adsorption, the adsorption capacity, and the adsorption kinetics in pH= 2 and pH= 6.5 for manganese, nickel, and cobalt ions. An increase of 5.47 times in manganese adsorption capacity was found after only 30 min in contact with a solution having this ion at pH= 6.5 for PUF-5 and 11.38 times for PUF-10 when both were compared with PUF-0. Adsorption efficiency was respectively 68.17% at pH= 2 for PUF-5% and 100% for PUF-10 after 120 h, while for the control foam, PUF-0, the adsorption efficiency was only 6.90%.

The Perspective and Challenge of Nanomaterials in Oil and Gas Wastewater Treatment

Oil and gas wastewater refers to the waste stream produced in special production activities such as drilling and fracturing. This kind of wastewater has the following characteristics: high salinity, high chromaticity, toxic and harmful substances, poor biodegradability, and a difficulty to treat. Interestingly, nanomaterials show great potential in water treatment technology because of their small size, large surface area, and high surface energy. When nanotechnology is combined with membrane treatment materials, nanofiber membranes with a controllable pore size and high porosity can be prepared, which provides more possibilities for oil–water separation. In this review, the important applications of nanomaterials in wastewater treatment, including membrane separation technology and photocatalysis technology, are summarized. Membrane separation technology is mainly manifested in ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO). It also focuses on the application of semiconductor photocatalysis technology induced by TiO₂ in the degradation of oil and gas wastewater. Finally, the development trends of nanomaterials in oil and gas wastewater treatment are prospected.

Novel strategy for membrane biofouling control in MBR with CdS/MIL-101 modified PVDF membrane by in situ visible light irradiation

Novel control strategies for membrane biofouling with eco-friendly photocatalytic technology are critically needed in practical operation of membrane bioreactors (MBRs). In this study, a metal-organic frameworks (MOF) based photocatalytic membrane was firstly applied in an anammox MBR for a long-term biofouling control, where bacteria were inactivated and foulants were degraded simultaneously, with environmentally friendly and renewable visible light energy. By physicochemical characterization, the synthesized photocatalyst of CdS/MIL-101 showed superior visible-light photocatalytic ability, and the 1 wt% CdS/MIL-101 modified membrane C2 showed enhanced hydrophilicity and water permeability compared with the pristine membrane C0. In the long-term operation of anammox MBRs under waterproof lights irradiation, the filtration cycles of C2 (25-26 d) were obviously extended compared with C0 (10-14 d), while their average total nitrogen removal efficiencies were comparable up to 84%, indicating an excellent biofouling alleviation effect by using C2 with a satisfactory nitrogen removal performance maintained. By analysis of the biofilm on the fouled membranes, the organic foulants (especially extracellular polymeric substances) were degraded, and the live bacteria were inactivated effectively by the photocatalytic reactions of CdS/MIL-101 on C2. In the antimicrobial tests against model bacteria, C2 exhibited remarkable antimicrobial effect against both Gram-negative and Gram-positive bacteria with visible light irradiation by destruction of cell integrity with the inhibition rate of 92% for Escherichia coli and 95% for Staphylococcus aureus, respectively. In the model foulants (bovine serum albumin, sodium alginate, and humic acid) filtration tests, C2 showed higher antifouling capabilities, lower flux declining rates, and higher foulants rejection rates under visible light irradiation compared with C0. The reactive species of ·OH, e^- and h⁺ generated on C2 were verified to play the predominant role in the anti-biofouling processes by simultaneous bacteria inactivation and foulants degradation. The findings offer a novel insight into the biofouling controlling in MBRs by simultaneous bacteria inactivation and foulants degradation with an eco-friendly method.

A Floatable Piezo-Photocatalytic Platform Based on Semi-Embedded ZnO Nanowire Array for High-Performance Water Decontamination

HIGHLIGHTS

ZnO nanowires were securely immobilized onto a floatable photocatalytic platform, which had a uniform diameter (55 ± 5 nm) and length (1.5 ± 0.3 μm).An additional 20% of the probe pollutant (methylene blue) was degraded by piezocatalysis-assisted photocatalytic degradation.The crude oil pollutant was decomposed up to 20% within 6 h. Photocatalytic degradation attracts considerable attention because it is a promising strategy to treat pollutants from industrial and agricultural wastes. In recent years, other than the development of efficient photocatalysts, much effort has been devoted to the design of reliable and inexpensive photocatalytic platforms that work in various environment conditions. Here, we describe a novel photocatalytic platform that is able to float and freely move atop water while performing photodegradation. Compared to common platforms, such as slurry reactors and immobilized photoreactors, the proposed platform is advantageous in terms of easy recycling and energy saving. Furthermore, the special configuration resulting from a two-step synthesis route, semi-embedded photocatalysts, addresses some of the remaining challenges, for instance, the contamination from the loose photocatalysts themselves. For the probe pollutant, methylene blue (MB), a reproducible and remarkable degradation activity of the platform, is observed and the effect of two primary factors, including surface area of the catalyst and mass transfer rate, is investigated. Besides, the piezo-photocatalysis effect, serving as an additional functionality, is confirmed to further improve the degradability of the platform, which offers an additional 20% of degraded MB. At last, the promising result of the degradation toward crude oil reveals the possibility of the platform to be used in gasoline pollution treatment.

TiO2-SiO2-PMMA Terpolymer Floating Device for the Photocatalytic Remediation of Water and Gas Phase Pollutants

Floating photocatalytic devices are highly sought-after as they represent good candidates for practical application in pollutant remediation of large water basins. Here, we present a multilayer floating device for the photocatalytic remediation of contaminants present in water as well as of volatile species close to the water surface. The device was prepared on a novel tailored ter-polymer substrate based on methylmethacrylate, α-methylstyrene and perfluoroctyl methacrylate. The ad hoc synthesized support presents optimal characteristics in terms of buoyancy, transparency, gas permeability, mechanical, UV and thermal stability. The adhesion of the TiO2 top layer was favoured by the adopted casting procedure, followed by a corona pre-treatment and by the deposition of an intermediate SiO2 layer, the latter aimed also at protecting the polymer support from photocatalytic oxidation. The device was characterized by contact angle measurement, UV-vis transmittance and scanning electron microscopy. The final device was tested for the photocatalytic degradation of an emerging water pollutant as well as of vapors of a model volatile organic compound. Relevant activity was observed also under simulated solar irradiation and the device showed good stability and recyclability, prospecting its use for the photocatalytic degradation of pollutants in large water basins.