Oilfield produced water (OPW) is one of the most important by-products, resulting from oil and gas exploration. The water contains a complex mixture of organic and inorganic compounds such as grease, dissolved salt, heavy metals as well as dissolved and dispersed oils, which can be toxic to the environment and public health. This article critically reviews the complex properties of OPW and various technologies for its treatment. They include the physico-chemical treatment process, biological treatment process, and physical treatment process. Their technological strengths and bottlenecks as well as strategies to mitigate their bottlenecks are elaborated. A particular focus is placed on membrane technologies. Finally, further research direction, challenges, and perspectives of treatment technologies for OPW are discussed. It is conclusively evident from 262 published studies (1965–2021) that no single treatment method is highly effective for OPW treatment as a stand-alone process however, conventional membrane-based technologies are frequently used for the treatment of OPW with the ultrafiltration (UF) process being the most used for oil rejection form OPW and oily waste water. After membrane treatment, treated effluents of the OPW could be reused for irrigation, habitant and wildlife watering, microalgae production, and livestock watering. Overall, this implies that target pollutants in the OPW samples could be removed efficiently for subsequent use, despite its complex properties. In general, it is however important to note that feed quality, desired quality of effluent, cost-effectiveness, simplicity of process are key determinants in choosing the most suitable treatment process for OPW treatment.
Membrane distillation (MD) is a burgeoning membrane technology that has gained immense interest among membrane scientists worldwide. Despite a slow start, both the theoretical and experimental researches on MD, especially on desalination applications, have escalated significantly over the past few decades. Although the large-scale use of MD has not proliferated worldwide, the researches done thus far have helped us to understand the rudiments of MD and explore the potential areas capable of enhancing its commercial attractiveness. Membranes of very high quality, nearing the properties of an ideal membrane, will fuel the growth of this technology. An ideal membrane for MD is expected to have features such as high liquid entry pressure, low fouling rate, low thermal conductivity, high permeability and excellent mechanical strength. In that regard, ceramic membranes have been appreciated for their high tolerance to harsh conditions, however, their high cost has rendered them less favourable commercially. Polymeric membranes are seen as a plausible cheaper alternative and have dominated research done thus far on MD. This review aims to give a brief introduction to MD and a summary of the research efforts to acquire the desired properties in polymeric membranes used in MD for desalination purposes. Potential research directions are highlighted too.
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In this numerical study, the performance of ceramic-based mullite hollow fiber (HF) membranes in a direct contact membrane distillation (DCMD) process was evaluated. Three types of membranes were tested: (i) hydrophobic membrane C8-HFM, (ii) rod-like omniphobic membrane (C8-RL/TiO2), and (iii) flower-like omniphobic membrane (C8-FL/TiO2). The CFD model was developed and validated with experimental results, which were performed over a 500 min period. The initial mass flux of C8-HFM was 30% and 9% higher than that of C8-FL/TiO2 and C8-RL/TiO2, respectively. However, the flower-like omniphobic membrane C8-FL/TiO2 had the lowest drop in flux, around 11%, while the rod-like omniphobic membrane C8-RL/TiO2 had a 15% reduction, both better than the 23% reduction in the hydrophobic membrane C8-HFM over the 500 min. The study also analyzed the impact of fouling by examining the variation in mass transfer coefficient (MTC) over time. The results indicated that the ceramic-based mullite HF membranes with TiO2 flowers and rods demonstrated a high resistance to fouling compared to C8-HFM. The modified membranes could find applications in the desalination and handling of seawater samples containing organic contaminants. The CFD model’s versatility can be utilized beyond the current investigation’s scope, offering a valuable tool for efficient membrane development solutions, particularly for challenges such as the presence of organic contaminants in seawater.
The presence of recalcitrant contaminants in water bodies such as heavy metals, dyes, pharmaceutical compounds, and chemical residuals results in water pollution. This requires the development of seminal water technologies including adsorptive membrane filtrations. This article critically reviews recent advances in adsorptive membrane technology for wastewater treatment. Particular focus is given on its fabrication and classification, surface characterizations, and their practical applications in removing target pollutants from aqueous solutions. Their advantages and limitations in applications are critically evaluated and compared. Their operational conditions such as pressure, initial pollutant concentration, and treatment performance are presented. Research trends, challenges, solutions, and the way forward for adsorptive membrane filtration are also elaborated. It is conclusively evident from 280 published studies (1971–2022) that integrated adsorption and membrane filtration processes were highly effective in removing refractory pollutants from contaminated wastewater due to their rapid adsorption-desorption rates, low internal diffusion resistance, and high flow rates. The sulfonic groups of the Nafion 117 membrane have a good adsorptive capacity to metal ions such as copper (II), nickel, cobalt, lead and silver ions with their adsorption capacities of 66, 64, 60, 58, and 47 mg/g, respectively. It is important to note that technical applicability, treatment performance, and treatment cost are critical factors in determining the most suitable water technology for treating wastewater laden with recalcitrant contaminants. Further research should address technical bottlenecks such as membrane fouling and agglomeration formation during the adsorptive membrane fabrication and operation. The constraints can be tackled to improve the quality of the membranes fabricated.
Every year, the global production of plastic waste reaches a staggering 400 million metric tons (Mt), precipitating adverse consequences for the environment, food safety, and biodiversity as it degrades into microplastics (MPs). The multifaceted nature of MP pollution, coupled with its intricate physiological impacts, underscores the pressing need for comprehensive policies and legislative frameworks. Such measures, alongside advancements in technology, hold promise in averting ecological catastrophe in the oceans. Mandated legislation represents a pivotal step towards restoring oceanic health and securing the well-being of the planet. This work offers an overview of the policy hurdles, legislative initiatives, and prospective strategies for addressing global pollution due to MP. Additionally, this work explores innovative approaches that yield fresh insights into combating plastic pollution across various sectors. Emphasizing the importance of a global plastics treaty, the article underscores its potential to galvanize collaborative efforts in mitigating MP pollution's deleterious effects on marine ecosystems. Successful implementation of such a treaty could revolutionize the plastics economy, steering it towards a circular, less polluting model operating within planetary boundaries. Failure to act decisively risks exacerbating the scourge of MP pollution and its attendant repercussions on both humanity and the environment. Central to this endeavor are the formulation, content, and execution of the treaty itself, which demand careful consideration. While recognizing that a global plastics treaty is not a panacea, it serves as a mechanism for enhancing plastics governance and elevating global ambitions towards achieving zero plastic pollution by 2040. Adopting a life cycle approach to plastic management allows for a nuanced understanding of possible trade-offs between environmental impact and economic growth, guiding the selection of optimal solutions with socio-economic implications in mind. By embracing a comprehensive strategy that integrates legislative measures and technological innovations, we can substantially reduce the influx of marine plastic litter at its sources, safeguarding the oceans for future generations.
The objective of this study is to produce superhydrophilic, low cost kaolin-based ceramic hollow fibre membrane (KHFM) for efficient oily-wastewater separation. The asymmetric KHFMs with short finger-like voids were successfully prepared via a combined phase inversion and sintering technique. It was observed that the increase in sintering temperature enhanced membrane mechanical strength and promoted significant changes on membrane morphology. The combination of hydrophilic characteristic (contact angle of 33°) and small pore size (0.35μm) of the kaolin KHFM sintered at 1500°C resulted in excellent oily wastewater separation, with a 100% success rate, thus indicating that KHFM is able to repel most of the oil and allow only water to pass through its pores. In conclusion, the developed KHFM can be regarded as a promising medium for oily wastewater separation.
Carbon dioxide (CO2) is the main culprit of greenhouse gases produced mainly via the combustion of fossil fuel. This paper reviewed the performance of emerging dual-layer hollow fiber membrane, its fabrication via co-extrusion process, improvement, challenges, spinning parameters, advantages and disadvantages in comparison to single-layer hollow fiber membrane for natural gas purification. Development of delamination-free dual-layer hollow fibers via co-extrusion and phase inversion technology is one of the potential solutions for the use of expensive and brittle polymers for the outer selective layer and low cost polymers with high thermal and mechanical properties for the porous inner layer.
Fouling tends to cause a significant increase in hydraulic resistance, decreased permeate flux, or increased transmembrane pressure (TMP) when a process is operated under constant TMP or constant flux conditions. To control membrane fouling and maintain sustainable operation, the concept of critical flux has been discussed by several researchers. Various fouling mechanisms, such as macromolecule adsorption, pore plugging, or cake build-up, as well as hydrodynamic conditions, for example aeration, can take place at the membrane surface. This study aimed to investigate the effects of mixed liquor suspended solid (MLSS) concentration and air bubble flow rate (ABFR) on the critical flux and fouling behavior, when treating refinery-produced wastewater. To determine the critical flux values, the experimental flux-steps were the following: (1) the filtration began with a 30 min step duration at a low flux (10 to 20 L/m2h); (2) at the end of this step (after 30 min), the permeate flux was increased, (3) this step was repeated until the TMP did not remain constant at the constant permeate flux, (4) the critical flux was then achieved. A critical flux model with an R2 of 0.9 was, therefore, derived, which indicates that the particle properties were regulated by the suspended solids. The increase of MLSS concentration, from 3 mg/L to 4.5 mg/L, resulted in a decrease of the permeate flux by 18%. Moreover, an increase in ABFR, from 1.2 mL/min to 2.4 mL/min, increased the permeate flux, but this decreased with a greater flow rate of aeration. To assess the stability and reversibility of fouling during critical flux (Jc) determination using a mixed matrix membrane, flux-step methods were utilized. A step height of 14.3 L/m2h and 30 min duration were arbitrarily chosen. The flux increased to 32.5 L/m2h with a slight increase of trans membrane pressure (TMP), while the rate of increase became significant at a higher flux of 143.6 L/m2h, due to fouling. Overall, this study proved that the response of MLSS concentration and aeration affected the membrane performance, based on the critical flux and fouling behavior.
