Sources, colloidal characteristics, and separation technologies for highly hazardous waste nanoemulsions.

Nanoemulsions play a crucial role in various industries. However, their application often results in hazardous waste, posing significant risks to human health and the environment. Effective management and separation of waste nanoemulsions requires special attention and effort. This review provides a comprehensive understanding of waste nanoemulsions, covering their sources, characteristics, and suitable treatment technologies, intending to mitigate their environmental impact. This study examines the evolution of nanoemulsions from beneficial products to hazardous wastes, provides an overview of the production processes, fate, and hazards of waste nanoemulsions, and highlights the critical characteristics that affect their stability. The latest advancements in separating waste nanoemulsions for recovering oil and reusable water resources are also presented, providing a comprehensive comparison and evaluation of the current treatment techniques. This review addresses the significant challenges in nanoemulsion treatment, provides insights into future research directions, and offers valuable implications for the development of more effective strategies to mitigate the hazards associated with waste nanoemulsions.

A comprehensive review on the behavior and evolution of oil droplets during oil/water separation by membranes.

Membrane separation technology has significant advantages for treating oil-in-water emulsions. Understanding the evolution of oil droplets could reveal the interfacial and colloidal interactions, facilitate the design of advanced membranes, and improve the separation performances. This review on the characteristic behavior and evolution of oil droplets focuses on the advanced analytical techniques, and the subsequent fouling as well as demulsification effects during membrane separation. A detailed introduction is provided on microscopic observations and numerical simulations of the dynamic evolution of oil droplets, featuring real-time in-situ visualization and accurate reconstruction, respectively. Characteristic behaviors of these oil droplets include attachment, pinning, wetting, spreading, blockage, intrusion, coalescence, and detachment, which have been quantified by specific proposed parameters and criteria. The fouling process can be evaluated using Hermia and resistance models. The related adhesion force and intrusion pressure as well as droplet-droplet/membrane interfacial interactions can be accurately quantified using various force analysis methods and advanced force measurement techniques. It is encouraging to note that oil coalescence has been achieved through various effects such as electrostatic interactions, mechanical actions, Laplace pressure/surface free energy gradients, and synergistic effects on functional membranes. When oil droplets become destabilized and coalesce into larger ones, the functional membranes can overcome the limitations of size-sieving effect to attain higher separation efficiency. This not only bypasses the trade-off between permeability and rejection, but also significantly reduces membrane fouling. Finally, the challenges and potential research directions in membrane separation are proposed. We hope this review will support the engineering of advanced materials for oil/water separation and research on interface science in general.

Destructing surfactant network in nanoemulsions by positively charged magnetic nanorods to enhance oil-water separation.

The separation of ultrafine oil droplets from wasted nanoemulsions stabilized with high concentration of surfactants is precondition for oil reuse and the safe discharge of effluent. However, the double barriers of the interfacial film and network structures formed by surfactants in nanoemulsions significantly impede the oil-water separation. To destroy these surfactant protective layers, we proposed a newly-developed polyethyleneimine micelle template approach to achieve simultaneous surface charge manipulation and morphology transformation of magnetic nanospheres to magnetic nanorods. The results revealed that positively charged magnetic nanospheres exhibited limited separation performance of nanoemulsions, with a maximum chemical oxygen demand (COD) removal of 50%, whereas magnetic nanorods achieved more than 95% COD removal in less than 30 s. The magnetic nanorods were also applicable to wasted nanoemulsions from different sources and exhibited excellent resistance to wide pH changes. Owing to their unique one-dimensional structure, the interfacial dispersion of magnetic nanorods was significantly promoted, leading to the efficient capture of surfactants and widespread destruction of both the interfacial film and network structure, which facilitated droplet merging into the oil phase. The easy-to-prepare and easy-to-tune strategy in this study paves a feasible avenue to simultaneously tailor surface charge and morphology of magnetic nanoparticles, and reveals the huge potential of morphology manipulation for producing high-performance nanomaterials to be applied in complex interfacial interaction process. We believe that the newly-developed magnetic-nanorods significantly contribute to hazardous oily waste remediation and advances technology evolution toward problematic oil-pollution control.

Coupling magnetic particles with flocculants to enhance demulsification and separation of waste cutting emulsion for engineering applications.

Magnetic particles were coupled with a flocculant to enhance the demulsification and separation of waste cutting emulsions. The optimal magnetic particle size and critical magnetic field conditions were investigated to achieve large-scale engineering application of magnetic demulsification separation for waste cutting emulsion treatment. The micro-scale magnetic particles were found to show comparable effects to nano-scale magnetic particles on enhancing the demulsification and separation of cutting emulsions, which are beneficial for broadening the selectivity of low-cost magnetic particles. The critical magnetic separation region was determined to be an area 40 mm from the magnetic field source. Compared to the flocculant demulsification, the magnetic demulsification separation exhibited a significant advantage in accelerating flocs-water separation by decreasing the separation time of flocs from 180-240 min to less than 15 min, compressing the flocs by reducing the floc volume ratio from 60%-90% to lower than 20%, and showing excellent adaptability to the variable properties of waste cutting emulsions. Coupled with the design of the magnetic disk separator, continuous demulsification separation of the waste cutting emulsion was achieved at 1.0 t/hr for at least 10 hr to obtain clear effluent with 81% chemical oxygen demand removal and 89% turbidity reduction. This study demonstrates the feasibility of applying magnetic demulsification separation to large-scale continuous treatment of waste emulsion. Moreover, it addresses the flocs-water separation problems that occur in practical flocculant demulsification engineering applications.

Acceleration of floc-water separation and floc reduction with magnetic nanoparticles during demulsification of complex waste cutting emulsions.

Waste cutting emulsions are difficult to treat efficiently owing to their complex composition and stable emulsified structure. As an important treatment method for emulsions, chemical demulsification is faced with challenges such as low flocs-water separation rates and high sludge production. Hence, in this study, Fe3O4 magnetic nanoparticles (MNPs) were used to enhance chemical demulsification performance for treating waste cutting emulsions under a magnetic field. The addition of MNPs significantly decreased the time required to attain sludge-water separation and sludge compression equilibrium, from 210 to 20 min. In addition, the volume percentage of sludge produced at the equilibrium state was reduced from 45% to 10%. This excellent flocculation-separation performance was stable over a pH range of 3-11. The magnetization of the flocculants and oil droplets to form a flocculant-MNP-oil droplet composite, and the magnetic transfer of the composite were two key processes that enhanced the separation of cutting emulsions. Specifically, the interactions among MNPs, flocculants, and oil droplets were important in the magnetization process, which was controlled by the structures and properties of the three components. Under the magnetic field, the magnetized flocculant-MNP-oil droplet composites were considerably accelerated and separated from water, and the sludge was simultaneously compressed. Thus, this study expands the applicability of magnetic separation techniques in the treatment of complex waste cutting emulsions.

[Effect of Constructed Wetland Configuration on the Removal of Nitrogen Pollutants and Antibiotics in Aquaculture Wastewater].

Horizontal subsurface flow constructed wetland (HSSFCW) and integrated vertical flow constructed wetland (IVFCW) consisted of down-flow and up-flow were built to treat aquaculture wastewater under different conditions. The water treatment performance, especially the nitrogen pollutants and antibiotics removal efficiencies, were compared, and the effects of flow patterns and hydraulic retention time (HRT) on the efficiencies were studied. The results showed that IVFCW had a better removal efficiency on nitrogen pollutants, and the removal rates of TN and NH4+-N were 58% and 80% (HRT=3 d), respectively. Microbial community was further analyzed using BIOLOG microplate technique and 454-pyrosequencing. The internal structure of IVFCW was conducive to the flow and dissolved oxygen condition, which induced higher microbial activity and diversity. The richness in Nitrospira distribution was the main reason for the removal efficiency of ammonia nitrogen. HRT had a great influence on the removal of NO3--N and NO2--N, and maintaining 3-4 d could reach good efficiency for all kinds of nitrogen pollutants. Solid phase extraction-high performance liquid chromatography-tandem mass spectrometry analysis (SPE-HPLC-MS/MS) was used to test the removal efficiency of antibiotics, and the results showed that there was no remarkable difference between the two configurations. The removal efficiency of Enrofloxacin was higher than that of Sulfamethoxazole and Florfenicol. Extending HRT from 1 d to 3 d could significantly improve the removal rate of Sulfamethoxazole, reaching above 50%.

Microbial selection pressure is not a prerequisite for granulation: dynamic granulation and microbial community study in a complete mixing bioreactor.

Microbial selection pressure is traditionally supposed as a prerequisite for aerobic granulation. This work gives a different insight on this issue. Fluorescent microspheres were used to label the flocculent biomass granulation for a period of 47days in a continuous-flow bioreactor. Analysis of the distribution of fluorescent microspheres in granules revealed that the terminal phase of granulation is in a dynamic steady state, where bioflocs detach, collide and aggregate randomly. This revealed that the un-granulated biomass was the result of the dynamic aggregation and breakage, rather than the microbial species unable to be granulated. Furthermore, denaturing gradient gel electrophoresis (DGGE) profile and UPGMA dendrogram results showed similar microbial communities during the granulation. To sum up, microbial selection pressure was not a prerequisite for aerobic granulation from both of the dynamic granulation steps and molecular biology aspects.