•Recent progress in enzymatic remediation of phenolic wastewaters have been reviewed.•Homogenous and heterogeneous enzymatic remediation processes have been addressed.•The impact of the key ...operational factors have been highlighted.•The key limitations and obstacles still faced by the process have been discussed.•Proposals for future research to address the unresolved challenges are included.
Water pollution is one of the serious environmental problems threatening the sustainable development of human civilization. Many phenolic compounds are hazardous, toxic, endocrine disrupting, mutagenic, teratogenic, and/or carcinogenic. They also cause severe damages to marine ecosystem. Accordingly, their removal from polluted wastewaters prior to its discharge to the environment is a mandatory task. Several processes have been proposed for treating phenol-contaminated waters. Among the proposed treatment processes is the enzymatic method. Thus, the key objective of this review article is to present the recent progress in utilizing peroxidases and laccases for the remediation of phenolic wastewaters. Both homogenous and heterogeneous enzymatic processes to remove different phenolic pollutants from wastewaters will be reviewed. Recent studies on the effects of the key operational factors (i.e., temperature and pH) will also be presented. Additionally, emerging trends in enzymatic wastewater treatment will be addressed. The obstacles and challenges facing the large scale applications of enzymatic remediation of phenolic wastewaters will be highlighted. More importantly, several ideas for addressing the limitations of the process and improving its efficiency and viability will be provided. These ideas might form the basis for future studies on developing a more effective enzymatic process for treating wastewaters contaminated with phenolic pollutants, which is a growing environmental problem worldwide.
•Pickering nanoemulsion formulation and characterization have been reviewed.•EOR mechanisms during Pickering nanoemulsion flooding have been analyzed.•The key operational factors and their impacts ...have been highlighted.•The key limitations and obstacles still faced by the process have been discussed.•Proposals for future research to address the unresolved challenges are included.
The key mechanisms in enhancing crude oil recovery include the reduction of interfacial tension (IFT) between the trapped crude oil and the injected flooding solution, the wettability alteration of the reservoir rocks, in-situ emulsification, pore plugging, mobility control, disjoining and capillary pressures, miscibility improvement, etc. Recently, Pickering nanoemulsions have emerged as attractive flooding fluids that can positively alter all the above mechanisms and, thus, provide an improved oil recovery relative to other tertiary methods. The nanoparticles (NPs) used to stabilize Pickering nanoemulsions must be carefully selected and engineered in order to impart the desired characteristics (e.g., stability, emulsion type, droplet size, zeta potential, etc.). Yet, the relationship between the efficacy of Pickering nanoemulsions in enhancing oil recovery and their characteristics is very complex and not fully understood. Additionally, the oil recovery enhancement mechanisms are quite complex and governed by several interrelated factors. Therefore, this article provides a state-of-the-art review of the formulations and applications of Pickering nanoemulsions for enhancing the recovery of crude oil, with a focus on the recovery mechanisms. Relevant recent studies on the topic have been analyzed and assessed in order to provide insights into the achieved progress and to highlight the remaining obstacles and challenges. Future research work to address the key obstacles and challenges has been proposed.
The dynamic adsorption of the anionic biosurfactant, surfactin, at the air–water interface has been investigated in this work and compared to those of two synthetic surfactants: the anionic sodium ...dodecylbenzenesulfonate (SDBS) and the nonionic octaethylene glycol monotetradecyl ether (C
14
E
8
). The results revealed that surfactin adsorption at the air–water interface is purely controlled by diffusion mechanism at the initial stage of the adsorption process (i.e.,
t
→
0
), but shifts towards a mixed diffusion-barrier mechanism when surface tension approaches equilibrium (i.e.,
t
→
∞
) due to the development of an energy barrier for adsorption. Such energy barrier has been found to be a function of the surfactin bulk concentration (increases with increasing surfactin concentration) and it is estimated to be in the range of 1.8–9.5 kJ/mol. Interestingly, such a trend (pure diffusion-controlled mechanism at
t
→
0
and mixed diffusion-barrier mechanism at
t
→
∞
) has been also observed for the nonionic C
14
E
8
surfactant. Unlike the pure diffusion-controlled mechanism of the initial surfactin adsorption, which was the case in the presence and the absence of the sodium ion (Na
+
), SDBS showed a mixed diffusion-barrier controlled at both short and long time, with an energy barrier of 3.0–9.0 and 3.8–18.0 kJ/mol, respectively. Such finding highlights the nonionic-like adsorption mechanism of surfactin despite its negative charge.
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•Stable crude oil/water nanoemulsions stabilized by biosurfactant are formulated.•The formulated nanoemulsions possess favorable characteristics for EOR applications.•At low shear ...rates, the emulsions showed shearing-thinning behavior.•At high shear rates, the emulsions showed shearing-thickening behavior,•Crude oil is completely recovered from the emulsion in < 1 h upon HCl addition.
The successful utilization of nanoemulsions in several applications would require the formulation of emulsions with excellent characteristics. Ideally, the nanoemulsions should be stabilized using bioemulsifiers, which do not negatively impact the environment throughout their cradle-to-grave lifetime. Thus, crude oil-in-water (O/W) nanoemulsions with exceptional properties were prepared in this study using rhamnolipid biosurfactant as a bioemulsifier. The obtained results reveal that rhamnolipid can produce O/W nanoemulsions with an average droplet size as low as 35.0 ± 6.6 nm. The nanoemulsions also have highly negative zeta potential, low interfacial tension, and long-term kinetic stability. Interestingly, almost all the formulated O/W nanoemulsions using different rhamnolipid dosages and oil/water ratios showed three different flow behaviors (i.e., shear-thinning, Newtonian, and shear-thickening at low, medium, and high shear rates, respectively). Additionally, the nanoemulsion formulated using 50/50 crude oil/water volumetric ratio displayed higher apparent viscosity than the crude oil at elevated temperatures (greater than 63 ⁰C). Furthermore, despite that all the formulated nanoemulsions were extremely stable, they can be easily, completely, and quickly (within ≤ 1 h) switched-off if needed via pH-switching. The results presented herein demonstrate the potential of biosurfactants for enhanced oil recovery (EOR) and other oilfield applications.
One of the limitations compromising the utilization of enzymes for the remediation of phenolic wastewaters is enzyme activity loss during the treatment. Some surface active additives have the ...potential to protect enzymes and, thus, improve their performance. In this study, the removal of bisphenol A from synthetic wastewater samples by laccase has been studied in the presence of rhamnolipid biosurfactant (RL), polyethylene glycol (PEG), Triton X-100, cetyltrimethylammonium bromide (CTAB), and sodium dodecylbenzenesulfonate (SDBS). The results demonstrated that the addition of 1 ppm RL provides the highest removal rate and removal extent of BPA. In the case of PEG and Triton X-100, the results showed that both additives have almost similar positive effects on the enzymatic remediation of BPA. However, unlike RL, the positive effects of PEG and Triton X-100 were appreciable only at higher concentration (i.e., 25 ppm). On the other hand, the addition of the two ionic surfactants (SDBS and CTAB) resulted in a negative effect on the enzyme activity and, thus, the remediation of BPA, demonstrating the undesirable interactions of these ionic surfactants with laccase. The negative effect of the charged additives was more pronounced for the case of the positively charged additive (i.e., CTAB).
Antimicrobial peptides (AMPs) are next generation antibiotics which will make excellent coating agents for a myriad of devices because they are far less susceptible to the development of pathogen ...resistance compared to conventional antibiotics, exhibit rapid and broad-spectrum killing profiles, and are effective at low concentrations. These advantages, however, are compromised upon AMP tethering to solid supports. The effects of peptide-tethering strategies in governing AMP orientation, surface density, flexibility, and activity are reviewed. Understanding AMP structure–function relationship in the tethered conformation will enable rational improvements of immobilisation parameters. Foreseeable challenges in the development of AMP-coated devices such as microbial accumulation on implant surface and the lack of direct biomolecular structure and orientation data of peptides on surfaces are also discussed, and solutions to address these roadblocks are also proposed.
Protein fouling is a serious problem in many food, pharmaceutical and household industries. In this work, the removal of rubisco protein fouling from cellulosic surfaces using a protease (subtilisin ...A) has been investigated experimentally and mathematically. The cellulosic surfaces were prepared using self-assembled monolayers (SAMs) on a surface plasmon resonance biosensor (chip) surface after conjugating cellulose to α-lipoic acid. Rubisco adsorption on the prepared cellulosic SAMs was found to be irreversible, leading to the creation of a tough protein fouling. The heterogeneous enzymatic cleansing of such tough fouling involves enzyme transfer to the surface and the subsequent removal of the rubisco via protease activity. In this work, these two processes were decoupled, allowing enzyme transfer and enzymatic surface reaction to be parameterized separately. Mathematical modeling of the enzymatic cleaning of protein fouling from cellulosic SAMs revealed that enzymatic mobility at the interface is an important factor. The approach presented in this work might be useful in designing better protein fouling-resistant surfaces. It could also be used to guide efforts to screen and gauge the cleaning performance of detergent–enzyme formulations.
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•The wide applications of clay minerals in water increased the treatment complexity.•Polyelectrolytes are environment friendly and can separate clay from wastewater.•Polyelectrolyte ...structures have a strong effect on the clay surface zeta potential.•The floc size of clay suspensions depends on the polyelectrolyte type.•Correlations between electrokinetics and the rheology of clays are established.
Separation of clay minerals from industrial wastewaters is of great academic and practical importance. Current treatment techniques are either not economically viable, not environmentally friendly, or both. Thus, researchers are actively trying to develop optimal and more environmentally friendly wastewater treatment processes. Clay minerals like montmorillonite, bentonite, kaolinite and illite have numerous applications in various industries including, mineral processing, cosmetics, pharmaceuticals, paint, dyes, cement, concrete, functional fillers, paper making, clarification of wines and oils, water treatment and improving drilling mud properties. Their wide applications increased the volume and treatment complexity of water contaminated with them since they form highly stable suspensions in water. Flocculating agents such as polyelectrolytes have the potential to separate the above-mentioned minerals from industrial wastewater effluents. Polyelectrolytes are more effective and environment-friendly flocculants, in contrast to inorganic metal salts and some non-biodegradable synthetic polymers that pose serious hazards to human health and the environment. The development of polyelectrolytes is considered to be among the most important breakthroughs in solid–liquid separation processes, which have resulted in an improved treatment of water polluted with minerals. In the characterization of clay mineral separation using polyelectrolytes, it has been common practice in the past to either emphasize on the flocculation behavior of colloidal clay-polyelectrolyte suspensions (i.e., settling behavior or floc sizes) or on the behavior of networked clay-polyelectrolyte suspensions (i.e., filterability or dewaterability of sediment). However, flocculation and rheological parameters, which are very important factors in optimizing the wastewater treatment process, have rarely been reported in the literature. The aim of this paper, therefore, is to offer a comprehensive review of the state-of-the-art contributions for polyelectrolyte systems, focusing on the development of different types of polyelectrolytes and their applications in flocculating and dewatering clay minerals. Electrokinetics and rheological behavior of different clay minerals using different polyelectrolytes are critically evaluated. The effect of several parameters related to the clay mineral (type, composition), the polyelectrolyte (e.g., synthetic/natural, molecular weight, charge type, charge density, linear vs branched) and the flocculation medium properties (e.g., pH, ionic strength, clay mineral and polyelectrolyte concentration and type) are reviewed. This paper provides up-to-date progress in the treatment of water contaminated with clay minerals using various polyelectrolytes. The gaps and potential parameters of investigation in flocculation optimization studies are identified and more economical and environmentally friendly reagents in wastewater treatment are highlighted.
There are two commonly used drilling fluids, namely water-based muds (WBMs) and oil-based muds (OBMs); however, the latter type is more desirable for drilling unconventional oilfield reserves. To ...account for the potential encounter of hydrogen sulfide (H2S) while drilling, the utilized OBMs should contain scavenger(s) with an effective H2S mitigation capability in order to in-situ capture this very lethal and corrosive gas. To the best of our knowledge, studies on incorporating H2S scavengers in OBMs and their testing are still greatly lacking in open literature. Thus, this study contributes into the filling of this gap by preparing a mineral oil-based drilling mud (MOBM) containing potassium permanganate as a promising, widely available, safe, and cheap H2S scavenger. The MOBM also comprised other ingredients including rhamnolipid biosurfactant as an emulsifier and octadecanethiol-modified (i.e., hydrophobized) zinc nanoparticles (serving as weighting agent). These materials have not been widely utilized so far in open literature for the preparation of MOBM. The results obtained from this study demonstrated that this mud could fully scavenge H2S for up to 22.7 h (i.e., breakthrough time), and it took about 63 h for the MOBM to become fully saturated with H2S. The scavenged amounts of H2S at these times reached 324.4 and 485.8 g/barrel MOBM, respectively. The formulated MOBM also displayed an appropriate non-Newtonian shear thinning behavior, where the apparent viscosity dropped sharply from about 1.96 to 0.71 Pa.s upon increasing the shear rate to from 1 to 10 s−1, followed by a gradual decrease down to 0.31 Pa.s at a shear rate of 1000 s−1. Additionally, the formulated mud is able to dissipate a significant amount of thermal energy as inferred from its estimated high activation energy of 34.93 kJ/mol, suggesting a good thermal stability of the MOBM. The present study reveals the possibility of formulating mineral OBMs with effective H2S for safely drilling sour oil and gas reservoirs.
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•Mineral oil-based drilling mud (MOBM) has been formulated.•It was stabilized by rhamnolipid biosurfactant as secondary emulsifier.•It contained hydrophobic zinc NPs as weighting agent.•It showed excellent H2S scavenging capacity and appropriate rheology.•It showed high activation energy and could significantly dissipate thermal energy.
Drilling issues such as shale hydration, high-temperature tolerance, torque and drag are often resolved by applying an appropriate drilling fluid formulation. Oil-based drilling fluid (OBDF) ...formulations are usually composed of emulsifiers, lime, brine, viscosifier, fluid loss controller and weighting agent. These additives sometimes outperform in extended exposure to high pressure high temperature (HPHT) conditions encountered in deep wells, resulting in weighting material segregation, high fluid loss, poor rheology and poor emulsion stability. In this study, two additives, oil wetter and rheology modifier were incorporated into the OBDF and their performance was investigated by conducting rheology, fluid loss, zeta potential and emulsion stability tests before and after hot rolling at 16 h and 32 h. Extending the hot rolling period beyond what is commonly used in this type of experiment is necessary to ensure the fluid's stability. It was found that HPHT hot rolling affected the properties of drilling fluids by decreasing the rheology parameters and emulsion stability with the increase in the hot rolling time to 32 h. Also, the fluid loss additive's performance degraded as rolling temperature and time increased. Adding oil wetter and rheology modifier additives resulted in a slight loss of rheological profile after 32 h and maintained flat rheology profile. The emulsion stability was slightly decreased and stayed close to the recommended value (400 V). The fluid loss was controlled by optimizing the concentration of fluid loss additive and oil wetter. The presence of oil wetter improved the carrying capacity of drilling fluids and prevented the barite sag problem. The zeta potential test confirmed that the oil wetter converted the surface of barite from water to oil and improved its dispersion in the oil.
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