Emulsified Oil Wastewater Research Articles

Treatment of emulsified oil wastewaters by using chitosan grafted magnetic nanoparticles

In this study, a class of chitosan (CS)-grafted magnetic nanoparticles (MNPs) was synthesized for treating emulsified oil wastewaters. Fe3O4 MNPs were synthesized by using a solvothermal method, followed by coating with aminopropyl-functionalized silica (APFS) to form a surface for further grafting of CS molecular chains. The synthesized MNPs were characterized by various technologies and their demulsification performances were evaluated under various conditions. Results showed that synthetic Fe3O4 MNPs showed negligible demulsification effect, however, under both acidic and neutral conditions, APFS-coated MNPs (Fe3O4@APFS MNPs) exhibited good demulsification effect via electrostatic attraction. It was also found that demulsification performance could be further enhanced upon CS grafting, especially under alkaline condition. Results showed that, under both acidic and neutral conditions, CS-grafted MNPs (Fe3O4@APFS-G-CS MNPs) could efficiently flocculate oil droplets mainly via electrostatic attraction, thereby facilitating magnetic separation; while under alkaline condition, MNPs could overcome electrostatic repulsion and be absorbed onto oil droplet surface via hydrophobic interaction, thereby exhibiting certain demulsification effect under magnetic field. Moreover, under both acidic and neutral conditions, synthesized MNPs could be recycled up to 7 cycles without showing significant loss in demulsification efficiency. In conclusion, CS-grafted MNPs can be easily synthesized and recycled, providing a potential promising approach for efficient treatment of emulsified oil wastewater.

Synthesis of pH-sensitive and recyclable magnetic nanoparticles for efficient separation of emulsified oil from aqueous environments

Emulsified oil wastewaters, arisen from oil industry and oil spill accidents, cause severe environmental and ecological problems. In this study, a series of pH-sensitive magnetic nanomaterials (MNPs) were synthesized and characterized for their evaluation in separation of emulsified oil from aqueous environments. A coprecipitation method was used to produce Fe3O4 magnetic nanoparticles that were coated in a 2-step process with first silica to form a surface for anchoring an (3-aminopropyl)triethoxysilane (APTES) molecular layer. Detailed studies were conducted on effects of MNPs dosage, APTES anchoring density (DA) and pH on oil-water separation performance of the synthetic MNPs. Results showed that, under both acidic and neutral conditions, MNPs with high DA exhibited enhanced oil-water separation performance, while under alkaline condition, the oil-water separation process was minimal. Alkaline conditions allowed the MNPs to be recycled up to 9 cycles without showing any significant decrease in oil-water separation efficiency. An examination of the oil-water separation mechanism found that electrostatic interaction and interfacial activity both played important roles in oil-water separation. In conclusion, pH-sensitive MNPs can be easily synthesized and recycled, providing a promising, cost-effective and environmentally-friendly process for the efficient treatment of emulsified oil wastewater.

Flocculation performance and mechanism of chitosan-based flocculants in the treatment of emulsified oily wastewater

ABSTRACTChitosan (CS)-based flocculants, denoted as CS-g-PAM and CS-g-PDBC, were successfully prepared via graft copolymerization of CS with acrylamide (AM) or dimethyl acryloyloxyethyl benzyl ammonium chloride (DBC). The grafting was confirmed by Fourier transform infrared spectroscopy (FTIR) and x-ray photoelectron spectroscopy (XPS). The flocculation performance of CS-g-PAM and CS-g-PDBC, as well as flocculants such as cationic polyacrylamide (CPAM), polyaluminum chloride (PAC), and CS, was evaluated and compared for treating emulsified oil wastewater. It was found that CS-g-PDBC exhibited excellent flocculation performance under both acidic and neutral conditions, while CS showed better flocculation ability under alkaline condition. The flocculation mechanism of CS and CS-g-PDBC was investigated via zeta potential measurements. Results showed that different flocculation mechanisms were involved at various pH levels. As regarding CS, the flocculation mechanism is mainly charge neutralization, patching, and sweep floc under acidic, neutral, and alkaline conditions, respectively, while for CS-g-PDBC, patching was the dominant mechanism under both acidic and neutral conditions.

Microscopic mechanism of membrane fouling in micro-filtration

The microscopic mechanism of the membrane fouling was studied using Poiseuille equation, Langmuir adsorption model and Darcy’s law. The experimental result showed that the change in membrane filtration resistance could be divided into three stages in a membrane bioreactor. The first stage was the adsorption and blocking of the membrane pore, and it is completed in a short time (t ≤ 1 min), so it was suitable to combine its resistance with the intrinsic membrane resistance. The second stage was the change in the concentration polarization during which the resistance increased rapidly. The resistance of the concentration polarization and the resistance of the gel layer were of same character and could be united by the Langmuir relationship. The third stage had stable filtration resistance when the deposition and proliferation of the pollutants on the membrane surface achieved a dynamical equilibrium. A unified model of membrane filtration was proposed for the three stages. The experimental data of the emulsified oil wastewater filtrated by micro-membrane fitted the unified model well.

A Coupling Process of Precoating Dynamic Membrane with Photocatalysis for Treatment of Oily Wastewater

In order to improve the steady permeate fluxes during the emulsified oil wastewater treatment using precoated dynamic membrane, a coupling process of precoating dynamic membrane with ultraviolet photocatalysis was studied. Impacts of the ultraviolet light power, pH values and the oil concentrations on improvement of the steady permeate fluxes were investigated. The results showed that the ultraviolet photocatalysis effectively improved the steady permeate fluxes and reduced the membrane fouling resistances during the emulsified oil wastewater treatment. The dynamic membrane steady membrane fluxes increased with the rise of ultraviolet light power and decrease in liquid pH values and oil concentrations. Impact of the ultraviolet photocatalysis on the oil retention ratio of precoating dynamic membrane was not obvious.

Performance of SIDMBR for Emulsified Oil Wastewater Treatment

The Sequencing Inclined Dynamic Membrane Biological Reactor (SIDMBR) was investigated on a pilot scale for 60 days of emulsified oil wastewater treatment at zero excess sludge discharge. Results indicate that at hydraulic retention time of 24 h, the average removals of chemical oxygen demand (COD), ammonia nitrogen and oil are 66.83, 64.2 and 70.8% in 1~60 days, respectively. The membrane flux, biofilm quantity, and extracellular polymeric substances (EPS) content begin to change after 20th, which indicate that membrane fouling has occurred.

Separation of oil from oily wastewater by modified resin

A new type of packing material, polystyrene resin modified by cetyltrimethyl-ammonium bromide (R-CTAB), was developed for separation of emulsified oil wastewater. The unique separation mechanism of the modified resin is due to the hydrogen bond formation between hydrocarbon molecules and the free hydrophilic part of the fixed surfactant. It changed the zeta potential of oil droplets and made them coalescing easier, which provide an optional choice without any chemicals added into the wastewater. A column of R-CTAB was investigated for its performance in separating emulsified oil droplets in oily wastewater. The effects of liquid space velocity and influent oil concentration were studied in particular. The results showed that R-CTAB column was more efficient than the un-modified resin column. Under the optimum experimental conditions, more than 85% of oil was removed by using R-CTAB column that at least 10% higher than the un-modified resin column.

The influence of nano-sized TiO 2 fillers on the morphologies and properties of PSF UF membrane

Polysulfone (PSF)/TiO 2 organic–inorganic composite UF membranes were successfully prepared by phase-inversion method with Nano-sized TiO 2 particles dispersed uniformly in 18 wt.% PSF casting solution. The influence of addition nano-sized TiO 2 particles on the morphologies and the properties of such PSF/TiO 2 membranes were investigated through the methods of SEM, XRD, DSC, contact angle goniometer, viscosity measurements, UF experiments and mechanical strength tests. The results showed that the rheological properties of casting solution were changed from Newtonian viscous behavior to non-Newtonian viscous behavior with an increasing viscosity of casting solution and the PSF/TiO 2 composite membranes exhibited differences in morphologies, porosities and properties due to nano-sized TiO 2 addition. At 2 wt.% TiO 2 content, the composite membranes held excellent water permeability, hydrophilicity, mechanical strength and good anti-fouling ability with almost unchanged retentions. The DSC and XRD analysis indicated that there were interactions between TiO 2 nanoparticles and polymers. However higher TiO 2 content (than 2 wt.%) caused a serious nanoparticle aggregation to result in the performances of PSF/TiO 2 membranes decline. The prepared membranes were also exhibited excellent ability to treat emulsified oil wastewater.

Effect of hydrophilicity on fouling of an emulsified oil wastewater with PVDF/PMMA membranes

Membranes with different degrees of hydrophilicity were prepared from PVDF and PMMA. The hydrophilicity was determined by using the contact angle technique. The distribution of pore radius was obtained from polydispersed solute permeation, scanning electron microscope (SEM) and hydraulic permeability. A higher hydrophilic character with the increase of PMMA in the casting solution and the appearance of larger macrovoids in the porous substructure were found without a substantial modification of the selective surface structure. However, a significant effect of compaction was evidenced due to the transmembrane pressure on membranes with high content of PMMA. An effluent from an engine factory was used to study the ultrafiltration performance of the prepared membranes. These assays show that membranes with a higher content of PMMA lead to a lower fouling.

Microfiltration of Emulsified Oil Wastewater

Hydrophilic polyvinylidenefluoride (PVDF) membranes were employed for emulsified oil wastewater treatment. The best operating conditions for optimum flux of water, which penetrates through the membrane and rejection (prevention of oil droplets from passing though the membrane) were obtained. Concentration and pH effects on flux and rejection were determined. Increase of weight concentration caused flux decline due to the formation of a thick layer on the membrane surface. However increasing the concentration increased rejection. The pH effects were complex. By increasing the acidity of the feed, rejection was reduced.

Pilot-Scale Ultrafiltration of an Emulsified Oil Wastewater

Wastewater from a household appliance factory containing emulsified oil was treated using a separation method based on an ultrafiltration membrane. Initial wastewater characteristics were a chemical oxygen demand (COD) of 1500 mg of O2/L and a total hydrocarbon concentration (HC) of 170 mg/L. The cross-flow pilot-scale study was performed with two commercial spiral-wound membrane modules having a molecular weight cutoff of 35 000 (M2 membrane) and of 2000 (M1 membrane). The M1 membrane showed COD and HC rejection performance higher than the M2 membrane. The M1 permeate flux and solute rejection were investigated in relation to the membrane pressure drop (ΔP = 100−400 kPa), temperature (20−35 °C), and feed cross-flow rate (2−5 m3/h). The permeate flux was in good agreement with the expression of Darcy's law, where the end-of-permeate flux is directly proportional to both applied pressure and temperature. Results indicate that the fouling layer resistance of the membrane was the dominant resistance and that it was mainly caused by the emulsified oil adsorption on the surface and/or in the pore wall of the membrane. For design purposes, correlations to estimate both permeate flux and COD-HC concentration in the retentate or permeate at any operational conditions (temperature, pressure, solution viscosity, concentration factor) have been obtained. Experimental pilot-scale tests had shown that an M1 ultrafiltration membrane is effective for removing emulsified oil and achieving up to 90.1% and 99.7% removal of COD and HC, respectively, with a permeate flux of 20 L h-1 m-2 at ΔP = 400 kPa and 35 °C. It is pointed out that by optimizing the process design utilizing this membrane module, it is possible to successfully apply the ultrafiltration membrane technology to the treatment of industrial emulsified oil waste effluents.

Investigation of Emulsified Oil Wastewater Treatment with Polymers

Wastewater from metal industry hot milling operations contains oil primarily from coolant sprayed on metal strips to dissipate heat during the rolling of metals. The emulsified oil wastewater for this study was withdrawn from two holding ponds where free oil would rise to the surface and was removed periodically, and used as influent for the chemical addition (CA)-gravity separation (GS) process. The principal objective of this research was to evaluate the effectiveness of different polymer addition systems through a CA-GS process for oil/grease (O/G) and total suspended solids (TSS) removal. Polymers from two corporations were investigated. A dual polymer system was recommended and supplied by Calgon Corporation—a cationic polymer (W-2923) to break the emulsion and an anionic polymer (POL-Z-E 2706) to enhance coagulation. A single polymer system was recommended and supplied by Grace Dearborn (GD) Corporation—a cationic polymer (KLAR-AID 2400) as a coagulant. Two types of experiments were performed: jar tests and larger scale batch-mixing tank (BMT) experiments. O/G and TSS removal efficiencies were 99% for both the Calgon and GD polymer systems. The range of optimum dosage was broader for the Calgon polymers, but both systems were susceptible to overdosing. A longer settling time was required for the GD polymer, but the Calgon polymers were more sensitive to pH. Average residual production rates were 89 and 148 gallons per 1000 gallons of wastewater treated for Calgon and GD polymers, respectively.