Fouling of Reverse Osmosis (RO) and Nanofiltration (NF) Membranes by Low Molecular Weight Organic Compounds (LMWOCs), Part 1: Fundamentals and Mechanism

Reverse osmosis (RO) and nanofiltration (NF) are ubiquitous technologies in modern water treatment, finding applications across various sectors. However, the availability of high-quality water suitable for RO/NF feed is diminishing due to droughts caused by global warming, increasing demand, and water pollution. As concerns grow over the depletion of precious freshwater resources, a global movement is gaining momentum to utilize previously overlooked or challenging water sources, collectively known as "marginal water". Fouling is a serious concern when treating marginal water. In RO/NF, biofouling, organic and colloidal fouling, and scaling are particularly problematic. Of these, organic fouling, along with biofouling, has been considered difficult to manage. The major organic foulants studied are natural organic matter (NOM) for surface water and groundwater and effluent organic matter (EfOM) for municipal wastewater reuse. Polymeric substances such as sodium alginate, humic acid, and proteins have been used as model substances of EfOM. Fouling by low molecular weight organic compounds (LMWOCs) such as surfactants, phenolics, and plasticizers is known, but there have been few comprehensive reports. This review aims to shed light on fouling behavior by LMWOCs and its mechanism. LMWOC foulants reported so far are summarized, and the role of LMWOCs is also outlined for other polymeric membranes, e.g., UF, gas separation membranes, etc. Regarding the mechanism of fouling, it is explained that the fouling is caused by the strong interaction between LMWOC and the membrane, which causes the water permeation to be hindered by LMWOCs adsorbed on the membrane surface (surface fouling) and sorbed inside the membrane pores (internal fouling). Adsorption amounts and flow loss caused by the LMWOC fouling were well correlated with the octanol-water partition coefficient (log P). In part 2, countermeasures to solve this problem and applications using the LMWOCs will be outlined.

Osmotic Force Balance Evaluation of Aqueous Electrolyte Osmotic Pressures and Chemical Potentials

Concentrated aqueous salt solutions are ubiquitous in problems of biological and environmental relevance. The development of accurate force fields that capture the interactions between dissolved species in solution is crucial to simulating these systems to gain molecular insights into the underlying processes under saline conditions. The osmotic pressure is a relatively simple thermodynamic property connecting the experimental and simulation measurements of the associative properties of the ions in solution. Milner [C. Gillespie and S. T. Milner, Soft Matter, 16, 9816 (2020)] proposed a simulation approach to evaluate the osmotic pressures of salts in solution by applying a restraint potential to the ions alone in solution and determining the resulting pressure required to balance that potential, referred to here as the osmotic force balance. Here, we expand Milner's approach, demonstrating that the chemical potentials of the salts in solution as a function of concentration can be fitted to the concentration profiles determined from simulation, additionally providing an analytical expression for the osmotic pressure. This approach is used to determine the osmotic pressures of 15 alkali halide salts in water from simulations. The cross interactions between cations and anions in solution are subsequently optimized to capture their experimental osmotic pressures.

Oilfield-produced water treatment using conventional and membrane-based technologies for beneficial reuse: A critical review

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 Bioreactors for Produced Water Treatment: A Mini-Review

Environmentalists are prioritizing reuse, recycling, and recovery systems to meet rising water demand. Diving into produced water treatment to enable compliance by the petroleum industry to meet discharge limits has increased research into advanced treatment technologies. The integration of biological degradation of pollutants and membrane separation has been recognized as a versatile technology in dealing with produced water with strength of salts, minerals, and oils being produced during crude refining operation. This review article presents highlights on produced water, fundamental principles of membrane bioreactors (MBRs), advantages of MBRs over conventional technologies, and research progress in the application of MBRs in treating produced water. Having limited literature that specifically addresses MBRs for PW treatment, this review also attempts to elucidate the treatment efficiency of MBRs PW treatment, integrated MBR systems, general fouling, and fouling mitigation strategies.

A novel antifouling technique for the crossflow filtration using porous membranes: Experimental and CFD investigations of the periodic feed pressure technique

Oily water production is one of the many drawbacks of petroleum and several other industries. Finding effective ways for the treatment of produced water remain one of the main areas of interest in membrane sciences. Albeit the many advantages of membrane technology, they suffer from the unavoidable problem of fouling, which results from the accumulation of dispersed materials at the surface of membranes. Membrane modification and operational optimization have been approached as a potential cure of the problem of fouling. In this work we introduce a new and novel method that minimizes the development of fouling and in the same time utilizes no chemicals (i.e., environmentally friendly). The core of this method is based on alternating the pressure in the feed channel in a periodic manner and is therefore named the periodic feed pressure technique, PFPT. The idea is to make pinned droplets at the surface of the membrane lose essential forces that keep them sticking to the surface. The drag force due to permeation flux and the capillary force due to interfacial tension represents the two forces that largely contribute to the pinning of oil droplets at the surface of the membrane. Other forces including buoyancy and lift forces are generally small to be of significant influence. The idea of the PFPT is, therefore, to eliminate the force due to permeation drag. This is done by setting the transmembrane pressure (TMP) to zero at fixed intervals allowing pinned oil droplets to dislodge the surface. When the TMP is set to zero, permeation flux stops and the force due to permeation drag vanishes. This significantly reduces the overall residence time of pinned oil droplets, minimizing the chance for other oil droplets to cluster and coalesce with pinned ones. The PFPT does not cause any damage to the support layer of the polymeric membrane, which is a drawback of back-flushing methodology. The novel PFPT displays minimal membrane fouling and very similar permeation recovery despite only half the cycle time is in filtration mode. In this work, we show how the permeation flux is recovered and provide comparisons between the PFPT and regular filtration methodology. Furthermore, we compare the overall amount of filtrate at the end of the experiments using both methods. It is interesting to note that, the amount of filtrate using the PFPT is very much comparable to that obtained using regular filtration methodology and even higher. By optimizing the frequency of the cycle and the amplitude of the pressure change, it is possible to customize the PFPT to various membrane technologies and to achieve the highest recovery of the flux. Visual inspections of the membranes post operation and post rinsing indicate that membranes undergoing filtration using the PFPT achieves a very clean surface compared with those undergoing regular filtration processes. This method is a promising solution to membrane fouling that is easy to implement without any additional use of chemicals or equipment. Computational fluid dynamics (CFD) investigation is also conducted on microfiltration processes to show why this technique works.

Application of neural networks in membrane separation

Artificial neural networks (ANNs) as a powerful technique for solving complicated problems in membrane separation processes have been employed in a wide range of chemical engineering applications. ANNs can be used in the modeling of different processes more easily than other modeling methods. Besides that, the computing time in the design of a membrane separation plant is shorter compared to many mass transfer models. The membrane separation field requires an alternative model that can work alone or in parallel with theoretical or numerical types, which can be quicker and, many a time, much more reliable. They are helpful in cases when scientists do not thoroughly know the physical and chemical rules that govern systems. In ANN modeling, there is no requirement for a deep knowledge of the processes and mathematical equations that govern them. Neural networks are commonly used for the estimation of membrane performance characteristics such as the permeate flux and rejection over the entire range of the process variables, such as pressure, solute concentration, temperature, superficial flow velocity, etc. This review investigates the important aspects of ANNs such as methods of development and training, and modeling strategies in correlation with different types of applications [microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), reverse osmosis (RO), electrodialysis (ED), etc.]. It also deals with particular types of ANNs that have been confirmed to be effective in practical applications and points out the advantages and disadvantages of using them. The combination of ANN with accurate model predictions and a mechanistic model with less accurate predictions that render physical and chemical laws can provide a thorough understanding of a process.

Treatment of Palm Oil Mill Effluent Using Membrane Bioreactor: Novel Processes and Their Major Drawbacks

Over the years, different types of alternative technologies have been developed and used for palm oil mill effluent (POME) treatment. Specifically, membrane bioreactor (MBR) has been employed to relegate pollutants contained in POME under different operating conditions, and the technology was found to be promising. The major challenge impeding the wider application of this technology is membrane fouling, which usually attracts high operating energy and running cost. In this regard, novel methods of mitigating membrane fouling through the treatment processes have been developed. Therefore, this review article specifically focuses on the recent treatment processes of POME using MBR, with particular emphasis on innovative processes conditions such as aerobic, anaerobic, and hybrid processing as well as their performance in relation to fouling minimization. Furthermore, the effects of sonication and thermophilic and mesophilic conditions on membrane blockage were critically reviewed. The types of foulants and fouling mechanism as influenced by different operating conditions were also analyzed censoriously.

Matrix acidizing: a fouling mitigation process in oil and gas wells

Fouling mitigation in underground reservoirs enhances the permeability and the flow capacity of production or injection wells and is carried out by reservoir stimulation methods such as matrix acidizing. This process is known as the most significant method used to improve the production or injection indices of oil and gas wells as well as water and steam wells. Here, different aspects of this process, its chemical advances and novel high-technologies are compared and discussed in order to reveal their advantages and determine under what conditions they are applicable. Knowledge for adapting the proper acid treatment with the well characteristics is another issue that has been considered in this paper. The final goal is to present the state-of-the-art fouling mitigation methods based on novel experiments, simulations and investigations in order to emphasize the engineering aspects of fouling mitigation in oil and gas wells by matrix acidizing.