Aquifer flushing using a SDS/1-butanol based in-situ microemulsion: Performance and mechanism for the remediation of nitrobenzene contamination

The effectivity and applicability of a novel sugar-based anionic and nonionic Gemini surfactant synthetized for the perchloroethylene-contaminated groundwater remediation

Surfactant-enhanced aquifer remediation (SEAR) has effectively removed dense nonaqueous phase liquids (DNAPLs) from the contaminated aquifers. However, restricted by structural defects, typical monomeric surfactants undergo precipitation, high adsorption loss, and poor solubilization in aquifers, resulting in low remediation efficiency. In this study, a novel sugar-based anionic and non-ionic Gemini surfactant (SANG) was designed and synthesized for SEAR. Glucose was introduced into SANG as a non-ionic group to overcome the interference of low temperature and ions in groundwater. Sodium sulfonate was introduced as an anionic group to overcome aquifer adsorption loss. Two long-straight carbon chains were introduced as hydrophobic groups to provide high surface activity and solubilizing capacity. Even with low temperature or high salt content, its solution did not precipitate in aquifer conditions. The adsorption loss was as low as 0.54 and 0.90 mg/g in medium and fine sand, respectively. Compared with typical surfactants used for SEAR, SANG had the highest solubilization and desorption abilities for perchloroethylene (PCE) without emulsification, a crucial negative that Tween80 and other non-ionic surfactants exhibit. After flushing the contaminated aquifer using SANG, > 99 % of PCE was removed. Thus, with low potential environmental risk, SANG is effectively applicable in subsurface remediation, making it a better surfactant choice for SEAR.

The beneficial health effects of puerarin in the treatment of cardiovascular diseases: from mechanisms to therapeutics

Cardiovascular diseases (CVDs) are the leading causes of death globally that seriously threaten human health. Although novel western medicines have continued to be discovered over the past few decades to inhibit the progression of CVDs, new drug research and development for treating CVDs with less side effects and adverse reactions are continuously being desired. Puerarin is a natural product found in a variety of medicinal plants belonging to the flavonoid family with potent biological and pharmacological activities. Abundant research findings in the literature have suggested that puerarin possesses a promising prospect in treating CVDs. In recent years, numerous new molecular mechanisms of puerarin have been explored in experimental and clinical studies, providing new evidence for this plant metabolite to protect against CVDs. This article systematically introduces the history of use, bioavailability, and various dosage forms of puerarin and further summarizes recently published data on the major research advances and their underlying therapeutic mechanisms in treating CVDs. It may provide references for researchers in the fields of pharmacology, natural products, and internal medicine.

Effect of cations on monochlorobenzene adsorption onto bentonite at the coexistence of Tween 80

The effect of several prevalent cations (including Na+, K+, Mg2+, Ca2+, Al3+, and Fe3+) on the adsorption of monochlorobenzene (MCB) onto bentonite was investigated at the coexistence of nonionic surfactant Tween 80 (T80) in surfactant-enhanced remediation (SER). They are all favorable for MCB and T80 adsorption, especially Mg2+ and Ca2+. Adsorption of MCB is strongly depended on T80 micelles. When its concentration exceeds the solubility, MCB is easier to bind with T80 micelles and be adsorbed by bentonite. Acidic environment can facilitate MCB and T80 adsorption, but the effect of cations on the adsorption is most significant under alkaline conditions. Adsorption capacity of MCB increases first followed by a slight decrease with increasing cations concentrations. The maximum adsorption rate of MCB determined is about 68.4% in a solution containing Mg2+ in the isothermal adsorption of MCB, while it is only 6.8% in a cation-free solution. Various characterizations showed that cations mainly changed the repulsion between bentonite particles and T80 micelles and the agglomeration and structure of bentonite, thus affecting the adsorption of MCB and T80 micelles. Our research demonstrated the nonnegligible promotion of MCB adsorption on bentonite by cations and acidic environment, which will adversely affect SER efficiency.

Enhancing remediation of residual DNAPL in multilayer aquifers: Post-injection of alcohol-surfactant-polymer mixtures

Although polymer-surfactant injection is an effective remediation technology for multilayer aquifers contaminated by Dense Non-Aqueous Phase Liquids (DNAPL), the existence of residual DNAPL after treatment is inevitable. This study evaluates the efficiency of the post-injection of alcohol-surfactant-polymer (ASP) mixtures containing 1-propanol/1-hexanol, sodium dodecylbenzenesulfonate (SDBS), and xanthan in enhancing remediation of residual DNAPL in layered systems. A range of experimental devices, including batch, rheological measurements, centimetric 1D column, and decametric 2D tank experiments, were employed. Batch experiments revealed that the inclusion of 1-hexanol swelled the DNAPL volume due to alcohol partitioning. Conversely, with only 1-propanol present in the alcohol-surfactant (AS) mixture, DNAPL dissolved in the aqueous phase. The co-presence of 1-hexanol along with 1-propanol in AS mixture favored 1-propanol's partitioning into the DNAPL phase. Column experiments, following primary xanthan-SDBS (XS) injections, demonstrated that ASP mixtures with 1-hexanol (regardless of presence of 1-propanol) underwent a mobilization mechanism. DNAPL appeared in the effluent as an organic phase after the post-injection of 0.3 pore-volumes (PV), by a reduction trend in its density. In contrast, mixtures with solely 1-propanol exhibited a solubilization mechanism, with DNAPL dissolving in the aqueous phase and emerging in the effluent after approximately 1 PV. 2D tank experiments visualized mobilization and solubilization mechanisms in multilayered systems. Post-injection of the ASP mixture with solely 1-propanol led to DNAPL solubilization, demonstrated by a dark zone of varied DNAPL concentrations, followed by a clearer white zone indicating significant DNAPL dissolution. Injecting ASP mixture containing both 1-propanol and 1-hexanol mobilized swollen DNAPL ganglia throughout layers, with these droplets coalescing and migrating to the recovery point. The darkness of mobilized droplets was faded as more DNAPL was recovered. The solubilization ASP mixture enhanced the recovery factor by 0.02 while the mobilization ASP mixture led to a 0.08 increase in the recovery factor.

Field demonstration of in-situ microemulsion flushing for enhanced remediation of multiple chlorinated solvents contaminated aquifer

The remediation of in-situ microemulsion flushing for multiple chlorinated solvents contaminated groundwater is challenging, because different chlorinated solvent has major influence on microemulsion formation and solubilization behaviors. This work was conducted to evaluate the remediation effectiveness for various chlorinated solvents contaminated site and monitor the disturbance of groundwater during in-situ microemulsion flushing process. Groundwater at this site was contaminated with chlorobenzene (MCB), chloroaniline and nitrochlorobenzene. The medium layer was mainly composed of fine and silty sand, with average hydraulic conductivity of 4.97 m/d. Results of this field-scale test indicated in-situ microemulsion flushing successfully enhanced the apparent solubility of various chlorinated solvents. Post-flushing concentration of various chlorinated solvents were 1.33-71.6-fold the concentration of pre-flushing values at 10 sampling locations within the test zone. This field was flushed with 16.8 m3 microemulsion, removing approximately 18.49 kg chlorinated solvents. Besides, a trend in the desorption order of various chlorinated solvents was observed. The least hydrophobic pollutant was flushed first, followed by contaminants of increasing hydrophobicity. In addition, during remediation process, the indexes of groundwater fluctuated insignificantly, indicating the reagent had little disturbance to aquifer. This field work demonstrated the feasibility of in-situ microemulsion enhanced remediation via increasing apparent solubility of multiple chlorinated solvents.

Fabrication of ballpoint-ink via encapsulating inorganic pigments in microemulsion gels

The fabrication of ballpoint-ink might open up a new perspective on physico-chemical solubility thermodynamics. In this report, we present a method to encapsulate inorganic pigments, such as Fe(CNS)3 (red), Fe2Fe(CN)6 (blue), CdS (yellow), and CuS (black) into w/o microemulsion gels. The area of w/o microemulsions was first determined by titrating surfactants Tween-60 into the given composition of water and cyclohexane in the pseudo-three phase diagram. Three prosperous phase areas were successfully mapped using this method, namely: microemulsion (w/o, and o/w) or (μE), lamellar liquid crystal (Lα), and hexagonal liquid crystal (Hα), respectively. The results show that inorganic pigments were well soluble in the w/o microemulsion gel of the Tween-60/cyclohexane/water system. The highest solubility of inorganic pigments in the microemulsion gel is 3.63 ± 0.05 mg g-1 for the red pigment of Fe(CNS)3, and the lowest is 2.92 ± 0.05 mg g-1 for the yellow pigment of CdS. Hence, the solubility limit distribution for all pigments is 2.9 ± 0.05 <>3.63 ± 0.05 mg g-1. The cation and anion size strongly affected the inorganic pigments' solubility in the w/o-microemulsion system. Some quantity of the ink-made of inorganic pigments encapsulated in the microemulsion gel has been inserted into empty ballpoint sleeves as prototypes. The resulting self-made inks demonstrated that the physical appearances of the ink could mimic the factory-made inks. Nevertheless, the self-made ink should be investigated further for long lifespan use, especially for long-term stability and corrosion resistance.

Synthetic and Natural Surfactants for Potential Application in Mobilization of Organic Contaminants: Characterization and Batch Study

In this paper, we investigated the abilities of five sugar-based synthetic surfactants and biosurfactants from three different families (i.e., alkyl polyglycoside (APG), sophorolipid (SL), and rhamnolipid (RL)) to dissolve and mobilize non-aqueous phase liquid (NAPL) components, i.e., toluene and perchloroethylene (PCE), adsorbed on porous matrices. The objective of this study was to establish a benchmark for the selection of suitable surfactants for the flushing aquifer remediation technique. The study involved a physicochemical characterization of the surfactants to determine the critical micelle concentration (CMCs) and interfacial properties. Subsequently, a batch study, through the construction of adsorption isotherms, made it possible to evaluate the surfactants’ capacities in contaminant mobilization via the reduction of their adsorptions onto a reference adsorbent material, a pine wood biochar (PWB). The results indicate that a synthetic surfactant from the APG family with a long fatty acid chain and a di-rhamnolipid biosurfactant with a shorter hydrophobic group offered the highest efficiency values; they reduced water surface tension by up to 54.7% and 52%, respectively. These two surfactants had very low critical micelle concentrations (CMCs), 0.0071 wt% and 0.0173 wt%, respectively; this is critical from an economical point of view. The batch experiments showed that these two surfactants, at concentrations just five times their CMCs, were able to reduce the adsorption of toluene on PWB by up to 74% and 65%, and of PCE with APG and RL by up to 65% and 86%, respectively. In general, these results clearly suggest the possibility of using these two surfactants in surfactant-enhanced aquifer remediation technology.