XDLVO Theory Research Articles

Towards a high-rate operation of contact stabilization process: Challenges of flocculation and floc stability

The high-rate contact stabilization (HiCS) process, a variant of high-rate activated sludge, has gained attention for its superior energy recovery and enhanced biosorption capabilities. The need for efficient energy recovery in HiCS necessitates a high settling efficiency to minimize resource loss due to endogenous sludge consumption. However, the low sludge retention time (SRT) required for HiCS can significantly affect sludge floc stability and flocculation performance, warranting a deeper analysis of the factors influencing these characteristics. This study investigates the impact of SRT reduction on sludge performance, focusing on energy potential, viscoelasticity, and critical pressure. The analysis was conducted using rheological tests, contact angle measurements, zeta potential analysis, Fourier transform infrared spectroscopy, XDLVO theory, and the PARAFAC model. Results indicate that due to the contribution of hydrophobicity, the HiCS system maintained the large flocs morphology of the sludge even when the SRT was maintained for 2d. However, a combination of aerobic microbial activity, high concentrations of loosely bound extracellular polymeric substances, and the presence of the filamentous bacterium Thiothrix contributed to reduced flocculation performance.

Enhanced gravity-driven membrane filtration for purifying roof rainwater using multi-walled carbon nanotubes tuned PVDF hollow fiber membranes

The collection and reuse of roof rainwater can alleviate water shortage for daily life. In this study, polyvinylidene fluoride hollow fiber membranes tuned with three multi-walled carbon nanotubes (pure MWCNTs, MWCNTs-COOH, and MWCNTs-OH) were prepared using a non-solvent induced phase separation method for gravity-driven membrane filtration to purify roof rainwater. The results showed that the MWCNTs were distributed on the membrane surface and throughout the porous structure of the cross-section, which changed the pore structure parameters and hydrophilicity. The pure water flux of the MWCNTs tuned membranes increased by 152.5 % at 1.0 bar, and the rejection rates of humic acid and bovine serum albumin increased from 97.4 % and 75.7 % to 98.9 % and 96.3 %, respectively. The extended Derjaguin, Landau, Verwey, and Overbeek (xDLVO) theory states that the presence of MWCNTs leads to changes in the physicochemical properties of the membrane surface, resulting in membranes with different anti-fouling behaviors. A gravity-driven membrane filtration test was continuously operated for 100 days, and all membranes removed 25.0–26.7 %, 49.5–53.0 %, and 89.0–93.3 % of total dissolved solids, dissolved organic carbon, and turbidity from roof rainwater, respectively. However, the pure MWCNTs modified membrane with relatively hydrophobic properties showed a 12.4 % increase in flux over the unmodified membrane. Importantly, the presence of the MWCNTs in the membrane changed the microbial diversity in the biofilter cake layer.

Effect of N-isopropylacrylamide and graphene oxide on the microstructure and performance of thermo-responsive membranes by Ce (IV)-induced redox radical polymerization

In this study, a series of novel thermo-responsive materials were synthesized using polyvinylidene fluoride, N-isopropylacrylamide (NIPAM) and graphene oxide (GO) via Ce (IV)-induced redox radical polymerization name as PNG. Thermo-responsive membranes were prepared by non-solvent induced phase separation. The results demonstrated that the CO and N-H stretching absorption intensities increased with the addition of NIPAM. XPS analysis demonstrated that the PNG1 membrane exhibited abundant functional group structure under the dosage of NIPAM at 1 g. The finger-like porous structure of membrane became longer and wider with the addition of NIPAM at 1 g, leading to a maximum porosity of 45.5 %. The CA decreased from 62.4 ° to 49.0 ° at 35 °C under the adding dosage of NIPAM at 1 g. The temperature-sensitive of PNG1 membrane was 35 °C. In addition, The PNG1 membrane had the lower Rir and higher flux recover than the others under the BSA rejection. According to the XDLVO theory analysis, the total interaction energy for PNG1 membrane achieved the maximum absolute values of −33.850 mJ/m2 and −19.956 mJ/m2 than the others under the temperature at 25 °C and 35 °C. This interaction influenced the adsorption between the pollutant and membrane surface, resulting in reversible fouling.

Impact of temperature and salinity on fines detachment: AFM measurements and XDLVO theory

Fine particle detachment and subsequent migration can lead to severe pore plugging and consequent permeability decline. Therefore, it is crucial to quantify the critical condition when fine particle detachment occurs. The frequently observed deviations or even contradictions between experimental results and theoretical predictions of fines detachment arise from an insufficient understanding of adhesion force that can be highly influenced by salinity and temperature. To clarify the intrinsic influence of salinity and temperature on fines detachment, adhesion forces between carboxyl microspheres and hydrophilic silica substrates in an aqueous medium were measured at various salinities and temperatures using atomic force microscopy (AFM). The AFM-measured adhesion force decreases with increasing salinity or temperature. Trends of mean measured adhesion forces with temperature and salinity were compared with the DLVO and XDLVO theories. DLVO theory captured the trend with temperature via the impact of temperature on electric double layer interactions, whereas XDLVO theory captured the observed trend with salinity via the impact of salinity on the repulsive hydration force. Our results highlight the significance of hydration force in accurately predicting the fate of fines in porous media.

The anti-fouling and mechanism of Fe3O4@PVDF catalytic membrane in-situ coupling Fenton oxidation for organic pollutants removal

Polyvinylidene fluoride (PVDF) membrane is a promising technique for deep treatment of organic wastewater. However, the unavoidable membrane contamination greatly restrictions its field of application. Herein, we successfully prepared Fe3O4@PVDF membrane with excellent anti-fouling and catalytic ability by non-solvent induced phase inversion method. Meanwhile, Fe3O4@PVDF membrane was characterized by SEM, XRD, FTIR, Water contact Angle and membrane aperture analyzer. The properties of separation and anti-fouling were also evaluated by cross flow filtration of humic acid (HA). Compare with pristine membrane, the pure water flux, rejection rate and FRR respectively increase from 556.81 L m-2 h−1, 65.42 %, 68.26 % to 656.96 L m-2 h−1, 99.64 %, 90.17 % under in-situ Fenton reaction condition. In addition, further mechanistic insights by XDLVO theory, 3D-EEM and EPR verified that high anti-fouling mainly attribute to excellent hydrophilicity of Fe3O4@PVDF and in-situ degradation of HA by OH and 1O2· This work provides insights for improving the separation properties and anti-fouling properties of PVDF membrane in the field of treatment organic wastewater.

A DFT-designed neodymium ion-imprinted membrane with fouling resistance and high flux

The rare earth metal neodymium (Nd) is widely used in advanced industries such as hybrid cars and aerospace. Therefore, recovering neodymium from wastewater presents valuable opportunities for secondary recycling. The recovery of Nd3+ from wastewater using ion imprinting technology (IIT) for efficient selective separation holds significant importance. In this study, hydrophilic Nd(III) ion-imprinted membranes, termed Nd(III)–P/P/TIIM, were synthesized using the IIT technique. Nd(III)–P/P/TIIM exhibited efficient and selective separation capabilities for Nd3+ with a remarkable retention rate of 95.68 % and a high water flux reaching up to 636.94 L·m−2·h−1. Additionally, its relative selectivity coefficients for interfering ions (KLa, KEu, KCu) were 3.9, 29.5, and 37.9, respectively. Various analyses, including DFT calculations, HOMO and LUMO calculations, MEP images, and XPS spectroscopy, confirm that the mechanism of selective retention of Nd3+ by Nd(III)–P/P/TIIM in solution is due to Coulombic adsorption between the –COO− anion and Nd3+ as well as an imprint memory effect. Even after undergoing three water-BSA cycles, the membrane maintained a water flux of 357.96 L·m−2·h−1. The antifouling principle of Nd(III)–P/P/TIIM was investigated by XDLVO theory, attributed to the increase of electron donor tension (γ−) and Lewis acid-base interactions (ΔGAB) at the membrane surface. This work provides an insightful guidance for engineering high-performance membranes and has the potential to provide an alternative method for recycling neodymium.

Adsorption and distribution of heavy metals in aquatic environments: The role of colloids and effects of environmental factors

The study investigated the distributions of heavy metals (Cd, Cr, Cu, Mn, and Pb) between dissolved fraction (<0.7 µm) and particles (>0.7 µm) during the adsorption process. The dissolved fraction was further separated into truly dissolved (<3 kDa) and colloidal (3 kDa-0.7 µm) fractions. Significant metal adsorption occurred on the colloids, resulting in their aggregation into particles, which in turn influenced the particle adsorption kinetics. Colloids could either accelerate or inhibit the transformation of metal ions into particulates, depending on their stability. Competitive metals for colloids (Pb and Cr) were more susceptible to the effects of colloids than other elements. DOM was the predominant environmental factor influencing colloid behavior. The XDLVO theory showed that DOM enhanced the negative charge of colloids and made the colloid surface more hydrophilic, inhibiting the aggregation of colloids. DOM resulted in substantial increases in the concentrations of colloidal Pb and Cr from 0.31 μg/L and 4.58 μg/L to 20.52 μg/L and 43.51 μg/L, respectively, whereas the increment for less competitive metals (Cd and Mn) was smaller. These findings suggest that the distribution of heavy metals is influenced not only by adsorption from particles and ions but also by the complex dynamics of colloids.

Modelling and application of dissolved air flotation for efficient separation of microplastics from sludges and sediments

The pervasive presence of microplastics in our environment necessitates urgent measures to prevent further release and address existing contamination hotspots. This work focuses on the removal of microplastics from sludges and sediments through the application of dissolved air flotation (DAF). In addition to experimental investigations, the study presents the development of a predictive model for the formation of aggregates comprising air bubbles and microplastics in the DAF contact zone. First an empirical model was established to predict the attachment efficiency between air bubbles and particles (αdb). To this end, the experimental attachment efficiency was determined for various plastics, with varying particle sizes and shape factors, and system conditions. The obtained data set was utilized to establish an empirical model by PLS regression describing αdb based on particle size, bubble size, density, Hamaker constant, contact angle, solid load, aspect ratio, circularity, and sphericity, resulting in an MSPE of 0.011 and adjusted-R² of 0.64. Secondly, a semi-deterministic model based on the XDLVO theory was developed using MLR, where αdb was described by the natural logarithm of the Van der Waals, electrostatic and hydrophobic forces acting between the particle and air bubble, and the solid load, with an RSE of 0.067 and adjusted-R² of 0.63. Finally, the applicability of these models was demonstrated in a case study on industrial sludge consisting of sediment and PVC microplastics. Validation of the attachment efficiency and the dimensioning of a DAF unit for processing this sludge at a capacity of 20 m³.h−1 emphasize the practical implications of the developed models.

Removal of silver colloids from radioactive wastewater by means of ultrafiltration

110mAg is the most common colloidal nuclide found in the radioactive liquid of nuclear power plants (NPPs). This paper investigates the morphology of silver colloids through a simulation experiment. The results show that the radionuclide 110mAg in the process water is reduced to Ag0 to form colloidal silver existing in regular shape with a size around 100 nm and a negative zeta potential. This zero-valent silver colloid can not be removed by the existing treatment process of ion exchange in NPPs effectively. One potential method for removal is ultrafiltration. The results demonstrate an effective removal of more than 98% of the silver colloids, accompanied by a flux increase of 146.9%. This is different from the traditional trade-off between membrane permeability and selectivity. Scanning electron microscopy (SEM) was utilized to study the membrane morphology, revealing a filtration mechanism that combines adsorption and sieving. The xDLVO theory was used to reveal the interfacial interaction between silver colloids and membrane materials. The results indicate that silver colloids can adsorb on the membrane surface spontaneously. The silver adsorbed by the membrane may form loose and hydrophilic silver colloids (an “aquifer”) and improve membrane hydrophilic and permeability properties simultaneously. The advantages of ultrafiltration on adsorption of silver colloids and improvement of water permeability provide a new method for the treatment of radioactive waste liquid containing colloidal silver.

Mutual role of dodecylbenzene sulfonic acid on enhanced oil recovery and asphaltene inhibition in low salinity medium: Experimental and XDLVO study

Understanding the molecular interactions during oil recovery processes can shed light on screening new chemicals for future operations. Of particular interest are chemicals capable of providing the mutual role of asphaltene inhibition and interfacial tension reduction at liquid–liquid and rock-liquid interfaces. This study delves into the interfacial interactions between low-salinity brines, model oils containing dodecylbenzene sulfonic acid, and dolomite rock surfaces. In the experimental part, the asphaltene precipitation inhibition efficacy of dodecylbenzene sulfonic acid was evaluated through filtration and precipitation test, and its oil recovery performance was examined from interfacial tension reduction and wettability alteration viewpoints. The theoretical part was then followed by the implementation of the surface energy concept based on the XDLVO theory, where acid-base and Lifshitz-van der Waals interaction energies, as well as the work of cohesion/adhesion between interacting bodies in asphaltene and oil recovery systems, were considered. The results obtained from this study revealed that dodecylbenzene sulfonic acid, owing to its acidic nature and the long alkyl chain in its structure, could simultaneously perform the role of asphaltene inhibitor and oil recovery agents. In particular, asphaltene particles showed less tendency to aggregate and form macrostructures in the presence of low-salinity brines formulated with magnesium chloride. The total interaction energy between asphaltene particles was almost halved by the addition of dodecylbenzene sulfonic acid. The low interfacial tension of 0.16 mN/m between model oil containing 1 wt% of DBSA and low-salinity brine containing 5000 mg/L magnesium chloride and the wettability alteration of the dolomite sample toward water-wetness were also confirmed by theoretical calculations using the concept of work of adhesion.

Investigating mechanism of enhanced anti-fouling performance of MXene modified Janus MD membrane by XDLVO theory combined with surface elemental integration method

Organic membrane fouling is a major obstacle to the application of membrane distillation in low surface tension wastewater treatment. Membrane modification might be an effective way to mitigate membrane fouling. This study mainly explored the mechanism of enhanced anti-fouling performance of the MXene modified PVDF membrane by applying XDLVO theory combined with surface elemental integration (SEI) method. The rough membrane surfaces were first reconstructed using fractal function. Then, the interaction energy between low surface tension substances and the membranes before and after modification was calculated. The results showed that oil droplets and surfactant fouling were mainly caused by hydrophobic attraction due to Lewis acid-base (AB) interaction energy. By modifying the virgin PVDF membrane with MXene nanoparticles, the polar component of membrane surface tension (γAB) increased significantly, so that the interaction energy between all contaminants and membrane surface changed from attraction to repulsion. In addition, roughness weakened the interaction energy between contaminants and membrane surface but significantly lengthened the range of interaction distance, which together determined the ability of the membrane to attract or repel the contaminants. These findings may improve the understanding of the structure-effect relationship between membrane modification and anti-fouling ability, and provide new insights into the membrane modification for MD.

Deciphering the behavior and potential mechanism of biochar at different pyrolysis temperatures to alleviate membrane biofouling

Biofouling limits applications of membrane technology in wastewater treatment, but dosing additives to membrane tanks is an effective method to alleviate biofouling. In this study, biochar derived from corncob and pyrolyzed at 300, 500, and 700°C was dosed to determine the underlying anti-biofouling mechanism. The effects of the biochar on the membrane properties and foulant behavior were systematically investigated. The results showed that biochar delayed the occurrence of the fouling transition (0.5–3.0 h), and decreased the flux decline rate, thus achieving a higher water flux (3.1–3.7 times of the control group). Biochar altered membrane surface properties, and increased the membrane surface charge, roughness, and hydrophilicity, which all contributed to higher membrane permeability. Moreover, adding biochar reduced the number of foulants in the fouling layer, particularly protein substances. The flux model fit and the XDLVO theory further revealed the mitigating effect of biochar on membrane biofouling. At the initial intermediate-blocking stage, the effect of biochar on membrane fouling was determined by its properties, and adsorption capacity to the foulants, BC500 presented the best mitigation performance. At the later cake-filtration stage, the role of biochar in membrane fouling was strongly associated with protein content in the fouling layer, and the minimum rate of flux decline occurred in BC300. This study promotes the understanding and development of biochar to alleviate membrane biofouling.

Biofilm formation and antioxidation were responsible for the increased resistance of N. eutropha to chloramination for drinking water treatment

Chloramination is an effective strategy for eliminating pathogens from drinking water and repressing their regrowth in water distribution systems. However, the inevitable release of NH4+ potentially promotes nitrification and associated ammonia-oxidizing bacteria (AOB) contamination. In this study, AOB (Nitrosomona eutropha) were isolated from environmental water and treated with two disinfection stages (chloramine disinfection and chloramine residues) to investigate the occurrence mechanisms of AOB in chloramination. The results showed that N. eutropha had considerable resistance to monochloramine compared to Escherichia coli, whose inactivation rate constant was 19.4-fold lower. The higher resistance was attributed to high levels of extracellular polymer substances (EPS) in AOB, which contribute to AOB surviving disinfection and entering the distribution system. In AOB response to the chloramine residues stage, the respiratory activity of N. eutropha remained at a high level after three days of continuous exposure to high chloramine residue concentrations (0.5–1.5 mg/L). Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) suggested that the mechanism of N. eutropha tolerance involved a significantly high expression of the intracellular oxidative stress-regulating (sodB, txrA) and protein-related (NE1545, NE1546) genes. Additionally, this process enhanced EPS secretion and promoted biofilm formation. Adhesion predictions based on the XDLVO theory corroborated the trend of biofilm formation. Overall, the naturally higher resistance contributed to the survival of AOB in primary disinfection; the enhanced antioxidant response of surviving N. eutropha accompanied by biofilm formation was responsible for their increased resistance to the residual chloramines.

Ageing regulates the migration of carbon nanotubes in saturated quartz sand

Ageing is the inevitable fate of carbon nanotubes (CNTs) in natural environments. However, the ageing-induced changes in the mobility of CNTs are still poorly understood. In this study, we investigated the migration of CNTs with different ageing degrees in saturated quartz sand using ultrapure water, fresh water and seawater as background solutions. Ageing could change the physicochemical properties of CNTs, leading to less hydrophobicity, lower hydrodynamic diameter, more negative charge and higher dispersity. As a result, aged CNTs exhibited a higher migration ability than pristine CNTs. Furthermore, DLVO theory and XDLVO theory were applied to explore the interaction between CNTs and between CNTs and quartz sand, respectively. Electrostatic repulsion is the primary force, and the total force is also repulsion and increases with ageing, which is favorable for CNTs to migrate in quartz sand. In fresh water and seawater, high ionic strength reduced the electrostatic repulsion, as well as hydrodynamic diameters and negative charges, and thus ageing exhibited a weaker enhancement on CNTs migration than that in ultrapure water. This work is useful to better understand the migration of aged CNTs and is of great significance to reveal the fate of carbon nanomaterials in nature.

Surface treatment to mitigate asphaltene deposition in wellbores using adhesion energy

The formation of sticky and hard asphaltene deposits in wellbores and flowlines is a severe and chronic problem that compromises oil productivity. One tangible solution that is gaining increased attention is to modify the interaction energy of surfaces such that would hinder deposition. While numerous studies have attempted to characterize mineral deposits in terms of surface energy, only a few investigations have performed similar studies for asphaltene deposition. In this study, asphaltene deposition on different substrates/coatings was analyzed from the interaction energy perspective. The surface energy components have been calculated using the van Oss approach and the respective adhesion energy was determined using the XDLVO theory. To do so, the adhesion energy was calculated for the interacting system of surface, asphaltene, and crude oil. The propensity of ten different substrates/coatings to deposition has been discerned for three crude oil samples of Z-55, K-42, R-95. The electron donor sub-component of the surface energy of crude oil was found to profoundly dominate the deposition of asphaltene on various investigated surfaces. The results also showed that different surfaces have distinct deposition affinity with respect to each crude oil. Thus, while a surface can be asphaltene-repellent for a specific crude oil, it could have affinity to deposition for another crude oil. Available data points from the field were also used to validate the obtained results.

Methods for the Characterization of the Colloidal Properties of Bacterial Membrane Vesicles.

Bacterial membrane vesicles (BMVs) are extracellular vesicles secreted by either Gram-positive or Gram-negative bacteria. These BMVs typically possess a diameter between 20 and 250nm. Due to their size, when these BMVs are suspended in another medium, they could be constituents of a colloidal system. It has been hypothesized that investigating BMVs as colloidal particles could help characterize BMV interactions with other environmentally relevant surfaces. Developing a more thorough understanding of BMV interactions with other surfaces would be critical for developing predictive models of their environmental fate. However, this bio-colloidal perspective has been largely overlooked for BMVs, despite the wealth of methods and expertise available to characterize colloidal particles. A particular strength of taking a more colloid-centric approach to BMV characterization is the potential to quantify a particle's attachment efficiency (α). These values describe the likelihood of attachment during particle-particle or particle-surface interactions, especially those interactions which are governed by physicochemical interactions (such as those described by DLVO and xDLVO theory). Elucidating the influence of physical and electrochemical properties on these attachment efficiency values could give insights into the primary factors driving interactions between BMVs and other surfaces. This chapter details methods for the characterization of BMVs as colloids, beginning with size and surface charge (i.e., electrophoretic mobility/zeta potential) measurements. Afterward, this chapter will address experimental design, especially column experiments, targeted for BMV investigation and the determination of α values.

Construction of chitosan modified cationic lipid droplet emulsions for high-value microalgae harvesting

To reduce the risk of microalgae biomass and environmental contamination, a natural cationic lipid droplet emulsion has been constructed for harvesting microalgae. Using three different microalgae strains (Chlorella vulgaris, Scenedesmus quadricauda and Spirulina platensis), the present work studied the influence of lipid droplet dosage, chitosan concentration, pH on harvesting efficiency, and then the flotation behavior was analyzed by zeta potentials, floc size distribution, algal organic matter component, attenuated total reflectance Fourier transform infrared spectrometer and microscopic observation. The XDLVO theory was used to explain the attachment behavior during the flotation process. The experimental results showed that the maximum harvesting efficiency for two green microalgae strains was over 95% at pH 7, while the optimal dosage and ratio of lipid droplet and chitosan were depended on the microalgae species. The maximum harvesting efficiency for Spirulina platensis was less than 70% since the high salinity of growth medium weakened the bridging and netting ability of chitosan. The mechanism of capturing microalgae by the ballasting agents was mainly physical electrostatic attraction, bridging and netting. In addition, the changes of microalgae components before and after harvesting were less than 5%, indicating this method would not affect the downstream application of microalgae biomass.

Enzyme-enhanced acidogenic fermentation of waste activated sludge: Insights from sludge structure, interfaces, and functional microflora

Anaerobic fermentation is widely installed to recovery valuable resources and energy as CH4 from waste activated sludge (WAS), and its implementation in developing countries is largely restricted by the slow hydrolysis, poor efficiency, and complicate inert components therein. In this study, enzyme-enhanced fermentation was conducted to improve sludge solubilization from 283 to 7728 mg COD/L and to enhance volatile fatty acids (VFAs) yield by 58.6 % as compared to the conventional fermentation. The rapid release of organic carbon species, especially for tryptophan- and tyrosine-like compounds, to outer layer of extracellular polymeric substance (EPS) occurred to reduce the structural complexity and improve the sludge biodegradability towards VFAs production. Besides, upon enzymatic pretreatment the simultaneous exposure of hydrophilic and hydrophobic groups on sludge surfaces increased the interfacial hydrophilicity. By quantitative analysis via interfacial thermodynamics and XDLVO theory, it was confirmed that the stronger hydrophilic repulsion and energy barriers in particle interface enhanced interfacial mass transfer and reactions involved in acidogenic fermentation. Meanwhile, these effects stimulate the fermentation functional microflora and predominant microorganism, and the enrichment of the hydrolytic and acid-producing bacteria in metaphase and the proliferation of acetogenic bacteria, e.g., Rubrivivax (+9.4 %), in anaphase also benefits VFAs formation. This study is practically valuable to recovery valuable VFAs as carbon sources and platform chemicals from WAS and agriculture wastes.

Reply to Comments on Investigation of Asphaltene Polydispersity, Stability, and Deposition on Steel Using XDLVO Theory

Reply to Comments on Investigation of Asphaltene Polydispersity, Stability, and Deposition on Steel Using XDLVO Theory

Comments on Investigation of Asphaltene Polydispersity, Stability, and Deposition on Steel Using XDLVO Theory

Comments on Investigation of Asphaltene Polydispersity, Stability, and Deposition on Steel Using XDLVO Theory