Investigation of flux stability and fouling mechanism during simultaneous treatment of different produced water streams using forward osmosis and membrane distillation

Fertilizer-driven FO and MD integrated process for shale gas produced water treatment: Draw solution evaluation and PAC enhancement

It is a great challenge for effective treatment of shale gas produced water (SGPW), a typical industrial wastewater with complex composition. Single forward osmosis (FO) or membrane distillation (MD) process has been widely used for desalination of SGPW, with membrane fouling not well addressed. Fertilizer draw solution (DS) with high osmotic pressure is less likely to cause FO fouling and can be used for irrigation. An integrated process using fertilizer-driven FO (FDFO) and MD process was proposed for the first time for SGPW treatment, and characteristics of fertilizer DS and powdered activated carbon (PAC) enhancement were assessed. The DS using KCl and (NH4)2SO4 had high MD fluxes (36.8-38.8 L/(m2·h)) and low permeate conductivity (below 50 μS/cm), increasing the contact angle of the MD membrane by 113 % than that without FO, while the DS using MgCl2 and NH4H2PO4 produced a lower reverse salt flux (0.9-3.2 g/(m2·h)). When diluted DS was treated using PAC, the MD permeate conductivity was further reduced to 35 μS/cm without ammonia, and the membrane hydrophobicity was maintained to 71-83 % of the original. The mechanism of the FDFO-MD integrated process for mitigating MD fouling and improving permeate quality was analyzed, providing guidance for efficient SGPW treatment.

Technical Feasibility of Extraction of Freshwater from Produced Water with Combined Forward Osmosis and Nanofiltration

This study assesses the technical feasibility of a forward-osmosis-based system for concentrating produced water and extracting freshwater. Forward osmosis was combined with nanofiltration, the latter system used to restore the initial osmotic pressure of the diluted draw solutions while concurrently obtaining the final freshwater product. Three draw solutions, namely, MgCl2, NaCl, and C3H5NaO2, were initially tested against a synthetic water mimicking a pretreated produced water effluent having an osmotic pressure equal to 16.3 bar. MgCl2 was thus selected for high-recovery experiments. Different combinations of draw solution osmotic pressure (30, 40, 60, 80, and 120) and draw-to-feed initial volume ratios (1, 1.6, and 2.2) were tested at the laboratory scale, achieving recovery rates between roughly 35% and 70% and water fluxes between 4 and 8 L m-2h-1. One-dimensional, system-wide simulations deploying the analytical FO water flux equation were utilized to validate the experiments, investigate co-current and counter-current configurations, and understand the system potential. The diluted draw solutions were then transferred to nanofiltration to regenerate their original osmotic pressure. There, the highest observed rejection was 96.6% with an average flux of 21 L m-2h-1, when running the system to achieve 100% relative recovery.

How high salt shock affects performance and membrane fouling characteristics of a halophilic membrane bioreactor used for treating hypersaline wastewater

In the present study, the effect of short-term salt shocks (13% and 20%) on the performance of a halophilic MBR bioreactor used to treat a hypersaline (5% salt) synthetic wastewater was considered. 13% and 20% salt shocks resulted in a transient and permanent decrease in chemical oxygen demand removal efficiency, respectively which could be correlated with soluble microbial products (SMP) concentration and specific oxygen uptake rate values of the halophilic population. DNA leakage tests suggested that both 13% and 20% short-term salt shocks resulted in some cell structural damage. During both 13% and 20% salt shocks mixed liquor SMP, extracellular polymeric substances (EPS), zeta potential and endogenous respiration increased while relative hydrophobicity, EPSp/EPSc and exogenous respiration decreased; in both cases, however, the pre-shock values for these parameters were restored after the removal of the salt shock. 13% salt shock resulted in a transient increase in the membrane fouling rate and a permanent rise in total membrane resistance (Rt). On the other hand, both membrane fouling rate and Rt increased during 20% salt shock. Membrane fouling rate initially reduced after the 20% salt shock removal but after 5 days a "TMP jump" occurred. The latter was caused by the higher steady state SMPc and SMPp concentrations after removal of 20% salt shock compared to pre-shock values. This might have either resulted in a decrease in critical flux or an increase in local flux above critical flux in some parts of the membrane. The contribution of cake layer resistance to overall membrane resistance increased after the 13% and 20% salt shocks. The findings of the present study reveal the robustness of halophilic MBRs against salt shocks in the treatment of hypersaline wastewater. However, in cases of very high salt shocks, appropriate membrane fouling reduction strategies should be carried out during its operation.

From waste to resource: Membrane technology for effective treatment and recovery of valuable elements from oilfield produced water

Oilfield produced water, a toxic and saline byproduct of the oil and gas industry, has become a global concern due to its adverse environmental and human health impacts. With large volumes of oilfiled produced water generated annually and predictions of even higher volumes in the near future, effective treatment and resource recovery are imperative. This review paper explores the potential of membrane technology, particularly integrated membrane systems, in treating and recovering valuable elements from oilfield produced water. The increasing attention to this topic is evident, but research on resource recovery still needs to be expanded. Membrane technology offers a promising solution due to its efficiency and minimal need for chemical additives or thermal inputs. However, challenges such as fouling, resistance to oil and organics, and economic viability must be addressed. By discussing oilfield produced water characteristics, treatment methods, practical applications, challenges, and prospects, this review underscores the transformative role of membrane technology in turning oilfield produced water into a valuable resource. Additionally, it emphasizes the importance of research in developing anti-fouling membranes, sustainable waste management techniques, and efficient cleaning protocols while considering economic implications and market dynamics for resource recovery.

Mineral scaling induced membrane wetting in membrane distillation for water treatment: Fundamental mechanism and mitigation strategies

The scaling-induced wetting phenomenon seriously affects the application of membrane distillation (MD) technology in hypersaline wastewater treatment. Unlike the large amount of researches on membrane scaling and membrane wetting, scaling-induced wetting is not sufficiently studied. In this work, the current research evolvement of scaling-induced wetting in MD was systematically summarized. Firstly, the theories involving scaling-induced wetting were discussed, including evaluation of scaling potential of specific solutions, classical and non-classical crystal nucleation and growth theories, observation and evolution of scaling-induced processes. Secondly, the primary pretreatment methods for alleviating scaling-induced wetting were discussed in detail, focusing on adding agents composed of coagulation, precipitation, oxidation, adsorption and scale inhibitors, filtration including granular filtration, membrane filtration and mesh filtration and application of external fields including sound, light, heat, electromagnetism, magnetism and aeration. Then, the roles of operation conditions and cleaning conditions in alleviating scaling-induced wetting were evaluated. The main operation parameters included temperature, flow rate, pressure, ultrasound, vibration and aeration, while different types of cleaning reagents, cleaning frequency and a series of assisted cleaning measures were summarized. Finally, the challenges and future needs in the application of nucleation theory to scaling-induced wetting, the speculation, monitoring and mitigation of scaling-induced wetting were proposed.

Quasi-critical condition to balance the scaling and membrane lifespan tradeoff in hypersaline water concentration

Mineral scaling is an inconvenient obstacle for membrane distillation in hypersaline wastewater concentration applications, compromising membrane lifespan to maintain high water recovery. Although various measures are devoted to alleviating mineral scaling, the uncertainty and complexity of scale characteristics make it difficult to accurately identify and effectively prevent. Herein, we systematically elucidate a practically applicable principle to balance the trade-off between mineral scaling and membrane lifespan. Through experimental demonstration and mechanism analysis, we find a consistent concentration phenomenon of hypersaline concentration in different situations. Based on the characteristics of the binding force between the primary scale crystal and the membrane, the quasi-critical concentration condition is sought to prevent the accumulation and intrusion of mineral scale. The quasi-critical condition achieves the maximum water flux on the premise of guaranteeing the membrane tolerance, and the membrane performance can be restored by undamaged physical cleaning. This report opens up an informative horizon for circumventing the inexplicable scaling explorations and develops a universal evaluation strategy to provide technical support for membrane desalination.

Interface interaction between silica and organic macromolecule conditioned forward osmosis membranes: Insights into quantitative thermodynamics and dynamics

Silica scaling is a rising concern in forward osmosis membrane-based water treatment process. The coexistence of ubiquitous organic macromolecules causes complex silica scaling. The silica scaling mechanism on the surface of the organic conditioned membrane remains unclear. An integrated multi scale thermodynamic and dynamic approach was used in this study to provide in-depth insights into the binding effect at the interface between the silica and the organic conditioned membrane at the molecular level. Sodium alginate (SA) was used as the model polysaccharide, bovine serum albumin (BSA) and lysozyme (LYZ) were chosen as two oppositely charged proteins. The results show that the silica scaling degree of different organic conditioned membranes follows the order LYZ > BSA > SA. The binding strength between silica and organic macromolecules and the membrane surface charge are the major factors governing the degree of silica scaling. Quartz crystal microbalance with dissipation (QCM-D), isothermal titration calorimetry (ITC), and extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) model analyses were conducted to quantify the binding capacity of silica to the organic conditioned membrane. The LYZ conditioned membrane exhibits the highest affinity for silica adsorption, and electrostatic interaction was the main molecular interaction force. This study provides fresh insights into how silica and an organic conditioned membrane interact and induce silica scaling, providing new information on potential mechanisms and control strategies to prevent membrane scaling.

Recovering and reuse of textile dyes from dyebath effluent using surfactant driven forward osmosis to achieve zero hazardous chemical discharge

This experimental study explores the feasibility of the reuse of dyes recovered from denim and polyester dyebath effluents using forward osmosis (FO) system to achieve zero hazardous material discharge. In batch experiments, the sodium dodecyl sulfate (SDS) at 0.5 M concentration generated an average flux of 3.5 L/m²/h (LMH) and reverse salt flux (RSF) of only 0.012 g/m²/h (GMH), while maintaining 100% dye rejection. This flux stability comes from the property of surfactants to form micelles and exert a stable osmotic pressure (π) above their critical micelle concentration (CMC). The low RSF is due to the greater micelle size. A colored fouling layer was formed on the membrane active layer (AL), which was easily removed using sodium hydroxide (NaOH) and citric acid. According to Fourier transform infrared spectra and atomic forces microscopy images of the AL, the interaction between foulants and membrane active groups did not significantly affect the physiochemical properties of the membrane. In the semi-continuous experiment, a very stable average flux of 7.3 LMH and RSF of 0.03 GMH was obtained using 0.75 M SDS as draw solution. The stacked 1D proton nuclear magnetic resonance analysis (¹HNMR) spectra of both original and recovered disperse dyes showed 100% similarity, which validates the concept that the recovered dyes maintained their integrity during reconcentration and can be reused in the next batch dyeing process. Importantly, the diluted SDS concentration can be directly reused within the same textile industry in scouring and finishing processes. The processes of dye recovery and reuse developed in this study do not produce any waste or hazardous by-products and are suitable for scale-up and onsite industrial applications.

Synergistic effects of microplastics and organic foulants on the performance of forward osmosis membranes

Microplastics (MPs) are emerging contaminants that are abundantly present in the influent and effluent of wastewater treatment plants (WWTPs). Forward osmosis (FO) is an advanced treatment technology with potential applications in WWTPs. The presence of MPs in WWTP effluents can contribute to FO fouling and performance deterioration. This study focuses on FO membrane fouling by MPs of different sizes, and the interactional impacts of MPs and Humic acid (HA) (as the most common organic foulant in WWTPs) on FO membrane performance. The synergistic effect of combined MPs and HA fouling is shown to cause higher flux decline for FO membranes than that of HA or MPs alone. Reverse salt flux increased in the presence of MPs, and decreased when HA was present. Further, full flux recovery was obtained for all fouled membranes after hydraulic cleaning. This indicates the efficiency of FO systems for treating wastewater with high fouling potential. This study highlights the necessity of considering MPs in studying fouling behaviour, and for mitigation strategies of membranes used in WWT. The fundamentals created here can be further extended to other membrane-assisted separation processes.

Coupling solar-driven interfacial evaporation with forward osmosis for continuous water treatment

Forward osmosis (FO) driven by osmotic pressure difference has great potential in water treatment. However, it remains a challenge to maintain a steady water flux at continuous operation. Herein, a FO and photothermal evaporation (PE) coupling system (FO-PE) based on high-performance polyamide FO membrane and photothermal polypyrrole nano-sponge (PPy/sponge) is developed for continuous FO separation with a steady water flux. The PE unit with a photothermal PPy/sponge floating on the surface of draw solution (DS) can continuously in situ concentrate DS by solar-driven interfacial water evaporation, which effectively offsets the dilution effect due to the injected water from FO unit. A good balance between the permeated water in FO and the evaporated water in PE can be established by coordinately regulating the initial concentration of DS and light intensity. As a consequence, the polyamide FO membrane exhibits a steady water flux of 11.7 L m-2 h-1 over time under FO coupling PE condition, effectively alleviating the decline in water flux under FO alone. Additionally, it shows a low reverse salt flux of 3 g m-2 h-1. The FO-PE coupling system utilizing clean and renewable solar energy to achieve a continuous FO separation is significantly meaningful for practical applications.

Desalinating a real hyper-saline pre-treated produced water via direct-heat vacuum membrane distillation

Membrane distillation (MD) is an emerging thermal desalination technology capable of desalinating waters of any salinity. During typical MD processes, the saline feedwater is heated and acts as the thermal energy carrier; however, temperature polarization (as well as thermal energy loss) contributes to low distillate fluxes, low single-pass water recovery and poor thermal efficiency. An alternative approach is to integrate an extra thermal energy carrier as part of the membrane and/or module assembly, which can channel externally provided heat directly to the membrane-feedwater interface and/or along the feed channel length. This direct-heat delivery has been demonstrated to increase single-pass water recovery and enhance the overall thermal efficiency. We developed a bench-scale direct-heated vacuum MD (DHVMD) process to desalinate pre-treated oil and gas "produced water" with an initial total dissolved solids of 115,500 ppm at a feed temperature ranging between 24 and 32 °C. We evaluated both water flux and specific energy consumption (SEC) as a function of water recovery. The system achieved a 50% water recovery without significant scaling, with an average flux >6 kg m^-2 hr^-1 and a SEC as low as 2,530 kJ kg^-1. The major species of mineral scales (i.e., NaCl, CaSO₄, and SrSO₄) that limited the water recovery to 68% were modeled in terms of thermodynamics and identified by scanning electron microscopy and energy-dispersive X-ray spectroscopy. In addition, we further developed and employed a physics-based process model to estimate temperature, salinity, water transport and energy flows for full-scale vacuum MD and DHVMD modules. Model results show that a direct-heat input rate of 3,600 W can increase single-pass water recovery from 2.1% to 3.1% while lowering the thermal SEC from 7,800 kJ kg^-1 to 6,517 kJ kg^-1 in an unoptimized module. Finally, the scaling up potential of DHVMD process is briefly discussed.

Recent Progress on Nanomaterial-Based Membranes for Water Treatment

Nanomaterials have emerged as the new future generation materials for high-performance water treatment membranes with potential for solving the worldwide water pollution issue. The incorporation of nanomaterials in membranes increases water permeability, mechanical strength, separation efficiency, and reduces fouling of the membrane. Thus, the nanomaterials pave a new pathway for ultra-fast and extremely selective water purification membranes. Membrane enhancements after the inclusion of many nanomaterials, including nanoparticles (NPs), two-dimensional (2-D) layer materials, nanofibers, nanosheets, and other nanocomposite structural materials, are discussed in this review. Furthermore, the applications of these membranes with nanomaterials in water treatment applications, that are vast in number, are highlighted. The goal is to demonstrate the significance of nanomaterials in the membrane industry for water treatment applications. It was found that nanomaterials and nanotechnology offer great potential for the advancement of sustainable water and wastewater treatment.