Recyclable Functional Magnetic Nanoparticles for Fast Demulsification of Waste Metalworking Emulsions Driven by Electrostatic Interactions

Complex multiphase waste metalworking emulsions, which contain large amounts of surfactants and mineral oil, are difficult to treat efficiently by traditional molecular demulsifiers. We synthesized one type of functionalized magnetic nanoparticles grafted with amino groups (M@NH₂) to treat waste metalworking emulsions from different mechanical processing factories and investigated the demulsification mechanism. The M@NH₂ showed an excellent demulsification performance, achieving 85–97% chemical oxygen demand (COD) removal for most of the waste metalworking emulsions. The results indicated the advantage of the three-step demulsification process (adsorption of M@NH₂ on droplets, droplet coalescence, and the magnetic transfer of droplets in the magnetic field) over traditional two-step demulsification (adsorption of MNPs on droplets and the transfer of droplets in the magnetic field). In addition, electrostatic interactions between M@NH₂ and surfactants were confirmed as the driving force of demulsification. Isothermal titration calorimeter quantified the interactions at the molecular level; the enthalpy was 1.83 kJ/mol, affinity coefficient between M@NH₂ and the surfactant was 1.5 × 10³, and the stoichiometric number of the surfactant and M@NH₂ was 11.5. This research provides a new perspective for the treatment of waste metalworking emulsions

Manipulation of Surface Hydrophobicity and Charge of Demulsifying Bacteria Using Functional Magnetic Nanoparticles: A Mechanistic Study of Demulsification Performance

Hydrophobicity and an electric charge are thought to be key factors that influence demulsification performance of demulsifying bacteria. Nonetheless, the exact mechanism of action of these two factors are not clear. Two series of functional magnetic nanoparticles with gradually varied hydrophobicity or surface charge were synthesized and combined with demulsifying bacteria, for manipulation of surface hydrophobicity or a charge of these bacteria. Demulsification results indicated that stronger cell surface hydrophobicity resulted in better demulsification performance of magnetically responsive bacterial demulsifiers (MRBDs), whereas a higher or lower surface charge (in the range from −30 mV to −20 mV) can inhibit it. Hydrophobicity accelerated droplet coalescence by 1.0 h in relation to its stimulatory effect on cell translocation to the interface. A proper surface charge made sure that bacteria aggregate to a certain extent at the interface. These results should be useful for broader applications of bacterial demulsifiers in the future

Use of horizontal subsurface flow constructed wetlands to treat reverse osmosis concentrate of rolling wastewater

<p>According to the characteristics of the reverse osmosis concentrate (ROC) generated from iron and steel company, we used three sets of parallel horizontal subsurface flow (HSF) constructed wetlands (CWs) with different plants and substrate layouts to treat the high-salinity wastewater. The plant growth and removal efficiencies under saline condition were evaluated. The evaluation was based entirely on routinely collected water quality data and the physical and chemical characteristics of the plants (<i>Phragmites australis, Typha latifolia, Iris wilsonii</i>, and <i>Scirpus planiculmis</i>). The principal parameters of concern in the effluent were chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP). The results showed that the CWs were able to remove COD, TN, and TP from ROC. <i>S. planiculmis</i> was not suitable for the treatment of high-saline wastewater. The sequence of metals accumulated in CW plants was K>Ca>Na>Mg>Zn>Cu. More than 70% of metals were accumulated in the aboveground of <i>P. australis</i>. The CW filled with gravel and manganese ore and planted with <i>P. australis</i> and <i>T. latifolia</i> had the best performance of pollutant removal, with average removal of 49.96%, 39.45%, and 72.01% for COD, TN, and TP, respectively. The effluent water quality met the regulation in China. These results suggested that HSF CW planted with <i>P. australis</i> and <i>T. latifolia</i> can be applied for ROC pollutants removal.</p

Cell surface properties of the demulsifying strain <i>Alcaligenes</i> sp. S-XJ-1 governing its behavior in oil–water biphasic systems

<div><p></p><p>Bacterial behavior in oil<b>–</b>water biphasic systems plays an essential role in hydrophobic contaminant degradation, oil recovery, and emulsion breaking. Less is known about the cell surface properties that govern their behaviors in oil–water biphasic systems. In this study, biphasic partitioning and aggregation of a demulsifying strain of <i>Alcaligenes</i> sp. S-XJ-1 were experimentally measured and evaluated based on the cell surface properties of surface charge, surface free energy, and cell surface hydrophobicity (CSH). The S-XJ-1 was cultivated with five different carbon sources, and the results showed a highly varied partitioning, aggregation behavior, and cell surface properties. The calculated interaction energies, based on the cell surface properties, were consistent with the results of their behavior. Among the cell surface properties, the electron-donor character (<i>γ</i>⁻, range 8.8–57.0 mJ/m²), which correlated well with CSH (Δ<i>G</i>_bwb), was an essential indicator of cell behavior. A low <i>γ</i>⁻ value enhanced the cell–interface and cell–cell interaction energies, which promoted cell partitioning and aggregation eventually leading to demulsification. The results and analysis provide important information for researchers concerned with cell–cell and cell–interface interactions.</p></div

Demulsification of a New Magnetically Responsive Bacterial Demulsifier for Water-in-Oil Emulsions

A new, magnetically responsive bacterial demulsifier (MRBD) was prepared by grafting magnetite (Fe₃O₄) nanoparticles onto the surface of demulsifying cells. The demulsification process and performance of the MRBD were investigated using a Turbiscan system. At a mass ratio of magnetite to demulsifying cells of 0.2, the demulsification ratio of MRBD increased from 70 to 80% in the presence of a magnetic field, the demulsification half-life decreased from 3.0 to 2.0 h, and the transmitted intensity increased 4 times compared with the native bacterial demulsifier. Analysis of the demulsification process revealed that an increased mass ratio improved the extent of drop coalescence by adjusting the balance between the surface hydrophobicity and magnetic responsiveness. The magnetic field mainly increased the drop sedimentation rate. The MRBD exhibited good recyclability and could be reused for three cycles, which may minimize demulsification costs. The simple synthesis and highly efficient demulsification performance represents a significant improvement over existing techniques