Removal of multiple pesticides from water by different types of membranes.

Pesticides are used in agriculture to protect crops from pathogens, insects, fungi and weeds, but the release of pesticides into surface/groundwater by agriculture runoff and rain has raised serious concerns not only for the environment but also for human health. This study aimed to investigate the impact of surface properties on the performance of seven distinct membrane types utilized in nanofiltration (NF), reverse osmosis (RO) and forward osmosis (FO) processes in eliminating multiple pesticides from spiked water. Out of the membranes tested, two are self-fabricated RO membranes while the rest are commercially available membranes. Our results revealed that the self-fabricated RO membranes performed better than other commercial membranes (e.g., SW30XLE, NF270, Duracid and FO) in rejecting the targeted pesticides by achieving at least 99% rejections regardless of the size of pesticides and their log Kow value. Despite the marginally lower water flux exhibited by the self-fabricated membrane compared to the commercial BW30 membrane, its exceptional ability to reject both mono- and divalent salts renders it more apt for treating water sources containing not only pesticides but also various dissolved ions. The enhanced performance of the self-fabricated RO membrane is mainly attributed to the presence of a hydrophilic interlayer (between the polyamide layer and substrate) and the incorporation of hydrophilic nanosheets in tuning its surface characteristics. The findings of the work provide insight into the importance of membrane surface modification for the application of not only the desalination process but also for the removal of contaminants of emerging concern.

Progress on Improved Fouling Resistance-Nanofibrous Membrane for Membrane Distillation: A Mini-Review.

Nanofibrous membranes for membrane distillation (MD) have demonstrated promising results in treating various water and wastewater streams. Significant progress has been made in recent decades because of the development of sophisticated membrane materials, such as superhydrophobic, omniphobic and Janus membranes. However, fouling and wetting remain crucial issues for long-term operation. This mini-review summarizes ideas as well as their limitations in understanding the fouling in membrane distillation, comprising organic, inorganic and biofouling. This review also provides progress in developing antifouling nanofibrous membranes for membrane distillation and ongoing modifications on nanofiber membranes for improved membrane distillation performance. Lastly, challenges and future ways to develop antifouling nanofiber membranes for MD application have been systematically elaborated. The present mini-review will interest scientists and engineers searching for the progress in MD development and its solutions to the MD fouling issues.

Assessment of contaminants in sand production from petroleum wells offshore Sabah.

Sand production remains a huge obstacle in many oil and gas fields around the world, but the hazards of contaminants riding on the produced sand are often not emphasised. Improper disposal of the sand could see the toxic leaching into the environment including the food chain, endangering all living organisms. The impending sand production from an oilfield offshore Sabah also suffers from the lack of hazards identification; hence, this study was conducted to assess the contaminant on the produced sand. Sand samples were collected from multiple wells in the area, with the contaminants extracted using n-hexane and subjected to chemical and thermal analyses. FTIR and GC-MS detected traces of harmful pollutants like naphthalene, amine substances, cyclohexanol, and short-chain alkanes. It was discovered that the volatile fraction of the contaminants was able to evaporate at 33 °C, while high energy was needed to remove 100% of the contaminants from the sand. Overall, the produced sand from the oilfield was unsafe and required treatment before it could be dumped or used.

Membranes prepared from graphene-based nanomaterials for water purification: a mini-review.

Graphene-based nanomaterials (GBnMs) are currently regarded as a critical building block for the fabrication of membranes for water purification due to their advantageous properties such as easy surface modification of functional groups, adjustable interlayer pore channels for solvent transportation, robust mechanical properties, and superior photothermal capabilities. By combining graphene derivatives with other emerging materials, heteroatom doping and rational design of a three-dimensional network can enhance water transportation and evaporation rates through channels of GBnM laminates and such layered structures have been applied in various water purification technologies. Herein, this mini-review summarizes recent progress in the synthesis of GBnMs and their applications in water treatment technologies, specifically, nanofiltration (NF) and solar desalination (SD). Finally, personal perspectives on the challenges and future directions of this promising nanomaterial are also provided.

A Review of Titanium Dioxide (TiO2)-Based Photocatalyst for Oilfield-Produced Water Treatment.

Oilfield produced water (OPW) has become a primary environmental concern due to the high concentration of dissolved organic pollutants that lead to bioaccumulation with high toxicity, resistance to biodegradation, carcinogenicity, and the inhibition of reproduction, endocrine, and non-endocrine systems in aquatic biota. Photodegradation using photocatalysts has been considered as a promising technology to sustainably resolve OPW pollutants due to its benefits, including not requiring additional chemicals and producing a harmless compound as the result of pollutant photodegradation. Currently, titanium dioxide (TiO2) has gained great attention as a promising photocatalyst due to its beneficial properties among the other photocatalysts, such as excellent optical and electronic properties, high chemical stability, low cost, non-toxicity, and eco-friendliness. However, the photoactivity of TiO2 is still inhibited because it has a wide band gap and a low quantum field. Hence, the modification approaches for TiO2 can improve its properties in terms of the photocatalytic ability, which would likely boost the charge carrier transfer, prevent the recombination of electrons and holes, and enhance the visible light response. In this review, we provide an overview of several routes for modifying TiO2. The as-improved photocatalytic performance of the modified TiO2 with regard to OPW treatment is reviewed. The stability of modified TiO2 was also studied. The future perspective and challenges in developing the modification of TiO2-based photocatalysts are explained.

Synthesis and Characterization of Titanium Dioxide Hollow Nanofiber for Photocatalytic Degradation of Methylene Blue Dye.

Environmental crisis and water contamination have led to worldwide exploration for advanced technologies for wastewater treatment, and one of them is photocatalytic degradation. A one-dimensional hollow nanofiber with enhanced photocatalytic properties is considered a promising material to be applied in the field. Therefore, we synthesized titanium dioxide hollow nanofibers (THNF) with extended surface area, light-harvesting properties and an anatase-rutile heterojunction via a template synthesis method and followed by a calcination process. The effect of calcination temperature on the formation and properties of THNF were determined and the possible mechanism of THNF formation was proposed. THNF nanofibers produced at 600 °C consisted of a mixture of 24.2% anatase and 75.8% rutile, with a specific surface area of 81.2776 m2/g. The hollow nanofibers also outperformed the other catalysts in terms of photocatalytic degradation of MB dye, at 85.5%. The optimum catalyst loading, dye concentration, pH, and H2O2 concentration were determined at 0.75 g/L, 10 ppm, pH 11, and 10 mM, respectively. The highest degradation of methylene blue dye achieved was 95.2% after 4 h of UV irradiation.

Exploring the effect of ultrasonic power, frequency, and load toward remediation of oil-contaminated beach and oilfield sands using ANOVA.

Despite the potential shown by previous investigations on the use of ultrasound for the remediation of oil-contaminated sand, the influence and interactions among ultrasonic parameters and oily sand are unclear, leading to possible ineffective treatment and high-power consumption. In order to improve the process efficiency, this work analyzes the effects of ultrasonic power, frequency, and load toward the cleaning of crude oil-contaminated sand, using two different sample positions and sand types. Crude oil-contaminated beach sand and produced sand from offshore oil well were used as samples. They were cleaned in custom-made ultrasonic bath reactor for 10 min with power from 30 to 120 W, frequency covering 25-60 kHz, and sand load of 10-100 g. With experimental design consisting multiple factors and levels, the interactions between factors in all possible combinations were determined using ANOVA (n = 210). From p-value based at 95% confidence interval and extensive F test, the three most significant factors were the sand type, the ultrasonic frequency, and the interaction between sand type and frequency. The best setting for suspended samples involved high frequency of 60 kHz, whereas bottom samples preferred low frequency at 28 kHz. This finding was justified when the acoustic pressure attenuation, standing wave pattern, and surface pitting/cracking were found in correlation with the cleaning results. Overall, the maximum treatment under ultrasonic bath solely gained around 60%, improvable by hybrid cleaning with other techniques such as chemical, biological, mechanical, and thermal.

Recent Mitigation Strategies on Membrane Fouling for Oily Wastewater Treatment.

The discharge of massive amounts of oily wastewater has become one of the major concerns among the scientific community. Membrane filtration has been one of the most used methods of treating oily wastewater due to its stability, convenience handling, and durability. However, the continuous occurrence of membrane fouling aggravates the membrane's performance efficiency. Membrane fouling can be defined as the accumulation of various materials in the pores or surface of the membrane that affect the permeate's quantity and quality. Many aspects of fouling have been reviewed, but recent methods for fouling reduction in oily wastewater have not been explored and discussed sufficiently. This review highlights the mitigation strategies to reduce membrane fouling from oily wastewater. We first review the membrane technology principle for oily wastewater treatment, followed by a discussion on different fouling mechanisms of inorganic fouling, organic fouling, biological fouling, and colloidal fouling for better understanding and prevention of membrane fouling. Recent mitigation strategies to reduce fouling caused by oily wastewater treatment are also discussed.

A Review on the Design and Performance of Enzyme-Aided Catalysis of Carbon Dioxide in Membrane, Electrochemical Cell and Photocatalytic Reactors.

Multi-enzyme cascade catalysis involved three types of dehydrogenase enzymes, namely, formate dehydrogenase (FDH), formaldehyde dehydrogenase (FaldDH), alcohol dehydrogenase (ADH), and an equimolar electron donor, nicotinamide adenine dinucleotide (NADH), assisting the reaction is an interesting pathway to reduce thermodynamically stable molecules of CO2 from the atmosphere. The biocatalytic sequence is interesting because it operates under mild reaction conditions (low temperature and pressure) and all the enzymes are highly selective, which allows the reaction to produce three basic chemicals (formic acid, formaldehyde, and methanol) in just one pot. There are various challenges, however, in applying the enzymatic conversion of CO2, namely, to obtain high productivity, increase reusability of the enzymes and cofactors, and to design a simple, facile, and efficient reactor setup that will sustain the multi-enzymatic cascade catalysis. This review reports on enzyme-aided reactor systems that support the reduction of CO2 to methanol. Such systems include enzyme membrane reactors, electrochemical cells, and photocatalytic reactor systems. Existing reactor setups are described, product yields and biocatalytic productivities are evaluated, and effective enzyme immobilization methods are discussed.

A Review on the Use of Membrane Technology Systems in Developing Countries.

Fulfilling the demand of clean potable water to the general public has long been a challenging task in most developing countries due to various reasons. Large-scale membrane water treatment systems have proven to be successful in many advanced countries in the past two decades. This paves the way for developing countries to study the feasibility and adopt the utilization of membrane technology in water treatment. There are still many challenges to overcome, particularly on the much higher capital and operational cost of membrane technology compared to the conventional water treatment system. This review aims to delve into the progress of membrane technology for water treatment systems, particularly in developing countries. It first concentrates on membrane classification and its application in water treatment, including membrane technology progress for large-scale water treatment systems. Then, the fouling issue and ways to mitigate the fouling will be discussed. The feasibility of membrane technologies in developing countries was then evaluated, followed by a discussion on the challenges and opportunities of the membrane technology implementation. Finally, the current trend of membrane research was highlighted to address future perspectives of the membrane technologies for clean water production.

Photocatalytic degradation of oilfield produced water using graphitic carbon nitride embedded in electrospun polyacrylonitrile nanofibers.

Separation and purification of oilfield produced water (OPW) is a major environmental challenge due to the co-production of the OPW during petroleum exploration and production operations. Effective capture of oil contaminant and its in-situ photodegradation is one of the promising methods to purify the OPW. Based on the photocatalytic capability of graphitic carbon nitride (GCN) which was recently rediscovered, photodegradation capability of GCN for OPW was investigated in this study. GCN was synthesized by calcination of urea and further exfoliated into nanosheets. The GCNs were incorporated into polyacrylonitrile nanofibers using electrospinning, which gave a liquid-permeable self-supporting photocatalytic nanofiber mat that can be handled by hand. The photocatalytic nanofiber demonstrated 85.4% degradation of OPW under visible light irradiation, and improved the degradation to 96.6% under UV light. Effective photodegradation of the photocatalytic nanofiber for OPW originates from synergetic effects of oil adsorption by PAN nanofibers and oil photodegradation by GCNs. This study provides an insight for industrial application on purification of OPW through photocatalytic degradation under solar irradiation.