Search Results (9)

Oily wastewater is extensively generated during the petroleum extraction and refining processes, as crude oil production water and from the effluent systems in petrochemical enterprises. The discharge standards for such wastewater are stringent, with the Oslo–Paris Convention stipulating that the oil content must be below 30 mg/L for permissible discharge. Flotation, a conventional oil–water separation method, relies on the collision and adhesion of rising bubbles with oil droplets in water to form low-density aggregates that float to the surface for separation. The collision and adhesion mechanisms between bubbles and oil droplets are fundamental to this process. However, systematic studies on their interactions remain scarce. This study employs the extended Derjaguin–Landau–Verwey–Overbeek theory to analyze the three mechanical interactions during the collision–adhesion process theoretically and investigates the heterogeneous interaction dynamics experimentally. Furthermore, given the diverse liquid-phase environments of oily wastewater, the effects of salinity, pH, and surfactant concentration are decoupled and individually explored to clarify their underlying mechanisms. Finally, a solution is proposed to enhance the flotation efficiency fundamentally. This work systematically elucidates the influence of liquid-phase environments on the adhesion behavior for the first time through the unification of theoretical and experimental approaches. The findings provide critical insights for advancing flotation theory and guiding the development of novel coagulants. Full article

There is a large amount of oil-contaminated wastewater caused by oil/gas production and marine oil spills. It is still a major challenge for the development of oil/water separating membranes that have excellent separation efficiency, can withstand saline environments, and have long-term durability. We present a new membrane made of ultralong titanate nanofibers (TNF) (with diameter of 200 nm and length of 60 µm) and carbon nanofibers (CNF) (with a diameter of 150 nm and length of 50 µm) for efficient and consistent oil/saltwater separation. The intertwined structure of titanate and carbon nanofibers is critical to ensuring a high mechanical strength and durability for the new membrane. The carbon nanofiber works as a scaffold in this membrane to maintain mechanical integrity during multiple cycles of reuses, which is an important merit for its practical applications. The ultralong titanate nanofibers work as functional component to provide high hydrophilicity of the membrane. The new membrane has an oil/water separation efficiency of more than 99%, an oil content in treated effluent that is lower than US environmental discharge standards (42 ppm), and a high water flux of 1520 LMH/bar, due to its excellent superhydrophilicity and inter-connected pore structure. The new membrane also exhibits outstanding durability in a variety of salinity environments, as well as good resistance to oil fouling. This new type of membrane has a high potential for industrial application in treating oily wastewater due to its excellent environmental durability, oil-fouling resistance, high separation efficiency, and easy scalability. Full article

Shale gas wastewater is a hypersaline industrial effluent in demand of efficient treatment or resource recovery. Membrane distillation (MD) is a heat-driven desalination process of high potential to deal with such streams. However, its application is highly limited by the unsatisfactory hydrophobic membranes that involve a trade-off between vapor permeability and fouling/wetting resistance. Our previous studies highlighted the potential role of an intermediate coating layer of a carbon nanotube (CNT) for the superhydrophobic membrane with 1H,1H,2H,2H-perfluorodecyltriethoxysilane (FAS) grafted to address the trade-off issue against synthetic saline oily wastewater. The work herein investigated its application performance in the continuous concentration and water recovery of real shale gas wastewater, with a commercial PVDF membrane as the reference. The modified membrane recycled 48.2% of the total volume as high-quality water and rejected 99% of feed salinity, achieving a superior concentration rate and flux recovery rate compared to PVDF. The value of the COD, total nitrogen, and ammonia nitrogen in the permeate after the modified membrane was less than 50, 20, and 20 mg/L, meeting the local wastewater discharge standard. It was pointed out that the inorganic fouling for the MD membrane was more of a concern in dealing with a real stream, but the modified membrane exhibited excellent fouling resistance. The cost associated with the treatment was estimated at USD 2.2/m³ for a production capacity of 2000 m³/d. The proposed superhydrophobic membrane has proven to be a feasible alternative from both technical and economic standpoints, offering the potential to improve MD effluent water quality and mitigate membrane fouling. Full article

We report the synthesis of reduced graphene oxide (rGO)-α-Fe₂O₃ nanocomposite and its application to remove and recover dissolved oil from a high-salinity oil–water emulsion in batch and column/breakthrough setups. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and nitrogen adsorption characterized the synthesized nanocomposite’s structure, morphology, and surface properties. Both batch and continuous breakthrough adsorption studies were investigated. The effect of the adsorption parameters on the adsorption capacity and removal efficiency was analyzed. The rGO-Fe₂O₃ nanocomposite (rGO-Fe₂O₃-NC) demonstrated a superior adsorption capacity, both when measured experimentally (1213 mg/g) and predicted using the Freundlich isotherm (1301 mg/g). The adsorption process followed pseudo-second-order kinetic, and the rGO-Fe₂O₃-NC exhibited a very rapid removal, with more than 60% of oil being removed within 10 min. Breakthrough confirmed the exceptional removal capacities with good regeneration and cycling ability under a short contact time. Moreover, the adsorption capacity was enhanced with an emulsion salinity of up to 100,000 ppm, confirming the suitability for high-salinity wastewater. Full article

Oily wastewater has been recognized as a threat to the environment due to its hazardous nature and it can negatively affect the ecosystem, and threaten wildlife and human health. Physical, chemical, and biological technologies demonstrated a mixed performance in oily wastewater treatment, and, therefore, a proper treatment technology for oily wastewater needs to be addressed. Membrane filtration using a hollow fiber (HF) membrane is a promising alternative to remove emulsified oil from oily wastewater. This review discusses different sources of oily wastewater, various treatment methods, and membrane technology. The assessment has been focused on the parameters affecting HF membrane performance and applications of HF membrane-based technology to treat oily wastewater. This review paper reveals that HF membrane filtration systems have been previously used for the treatment of oily wastewater in bench-scale studies and few pilot-scale applications, which proved to be favorable in the treatment of recalcitrant wastewater containing oil and high salinity. Limitations associated with membrane fouling and the reduction of membrane permeability and membrane lifespan can be tackled and alleviated through modifying membrane chemistry and adjusting operational parameters. The compilation of studies showed that a low food/microorganism (F/M) ratio, long solid retention time (SRT) with high sludge age, long hydraulic retention time (HRT), and moderate aeration were the preferred operational parameters when treating oily wastewater. Based on this review, future studies should focus on optimizing the hydrodynamic conditions of the HF system, the commercialization of modified HF membranes, and the utilization of green technology in HF membrane construction to broaden HF membrane technology applications. Full article

Bilge water is oily saline wastewater accumulated on the hull at the bottom of a vessel, generated from leakage from pipes and engines and wash-down freshwater containing cleaning solvents. The present study focused on isolating microorganisms from oil-contaminated sites and indigenous species from raw bilge water and assessment of their ability to biodegrade bilge water. Using phenanthrene as a carbon source Citrobacter species was isolated from oil-contaminated sites and its optimum growth condition was found. The results indicated significant tolerance of the bacterium which presented great biodegradation ability for the tested carbon source. At high salinity (33 g L⁻¹ of NaCl), sufficient phenathrene removal was achieved (81%), whereas variation of pH from 5 to 10 did not affected the survival of the microorganism. Regarding the effect of temperature and nutrients, Citrobacter sp. was better adapted at 30 °C, while lack of nutrients presented a negative impact on its growth. Halomonas and Exiguobacterium sp. were isolated from real bilge water using phenanthrene and phenol as a carbon source. The isolated strains independently exposed to high and low range bilge water pointed out around 83% and 53% chemical oxygen demand (COD) removal, respectively. Analysis of untreated bilge water by gas chromatography-mass spectrometry (GC-MS) was carried out, and the results confirmed the presence of organic compounds having a high similarity with Heptane, N-hexadecanoic acid, Methyl isobutyl Ketone and 1-butoxy-2-propanol. Chromatographic analysis of treated bilge water after exposure to isolated strains indicated the existence of new compounds. These metabolites presented high similarity with N-hexadecanoic, methyl ester, N-hexadecanoic and Octadecanoic acid methyl ester. Full article

In the present study, membrane distillation (MD) was applied for the treatment of oily saline wastewaters produced on ships sailing the Baltic Sea. For comparison purposes, experiments were also carried out with model NaCl solutions, the Baltic Seawater and oil in water emulsions. The commercial Accurel PP V8/2 membranes (Membrana GmbH, Germany) were used. In order to investigate the impact of the operational parameters on the process performance, the experiments were conducted under various values of the feed flow velocity (from 0.03 to 0.12 m/s) and the feed temperature (from 323 to 343 K). The obtained results highlight the potential of PP membranes application for a stable and reliable long-term treatment of oily wastewater. It was demonstrated that the permeate flux increased significantly with increasing feed temperature. However, the lower temperature ensured the limited scaling phenomenon during the treatment of oily wastewaters. Likewise, increasing the feed flow velocity was beneficial to the increase in the flux. Moreover, it was found that performing a cyclic rinsing of the module with a 3% HCl solution is an effective method to maintain a satisfactory module performance. The present study sheds light on improving the MD for the treatment of oily wastewaters. Full article

The components of waste cooking oil (WCO) are complex and contain toxic substances, which are difficult to treat biologically. Pseudomonas aeruginosa WO2 was isolated from oily sludge by an anaerobic enrichment–aerobic screening method, which could efficiently utilize WCO and produce rhamnolipid. The effects of nutrients and culture conditions on bacterial growth and lipase activity were investigated to optimize the fermentation of WCO. The results showed that strain WO2 utilized 92.25% of WCO and produced 3.03 g/L of rhamnolipid at 120 h. Compared with inorganic sources, the organic nitrogen source stabilized the pH of fermentation medium, improved lipase activity (up to 19.98 U/mL), and promoted the utilization of WCO. Furthermore, the WO2 strain exhibited inferior utilization ability of the soluble starch contained in food waste, but superior salt stress up to 60 g/L. These unique characteristics demonstrate the potential of Pseudomonas aeruginosa WO2 for the utilization of high-salinity oily organic waste or wastewater. Full article

With the blooming of oil and gas industries, oily saline wastewater treatment becomes a viable option to resolve the oily water disposal issue and to provide a source of water for beneficial use. Reverse osmosis (RO) has been touted as a promising technology for oily saline wastewater treatment. However, one great challenge of RO membrane is fouling phenomena, which is caused by the presence of hydrocarbon contents in the oily saline wastewater. This study focuses on the fabrication of antifouling RO membrane for accomplishing simultaneous separation of salt and oil. Thin film nanocomposite (TFN) RO membrane was formed by the layer by layer (LbL) assembly of positively charged TNS (pTNS) and negatively charged TNS (nTNS) on the surface of thin film composite (TFC) membrane. The unique features, rendered by hydrophilic TNS bilayer assembled on TFC membrane in the formation of a hydration layer to enhance the fouling resistance by high concentration oily saline water while maintaining the salt rejection, were discussed in this study. The characterization findings revealed that the surface properties of membrane were improved in terms of surface hydrophilicity, surface roughness, and polyamide(PA) cross-linking. The TFC RO membrane coated with 2-bilayer of TNS achieved >99% and >98% for oil and salt rejection, respectively. During the long-term study, the 2TNS-PA TFN membrane outperformed the pristine TFC membrane by exhibiting high permeability and much lower fouling propensity for low to high concentration of oily saline water concentration (1000 ppm, 5000 ppm and 10,000 ppm) over a 960 min operation. Meanwhile, the average permeability of uncoated TFC membrane could only be recovered by 95.7%, 89.1% and 82.9% for 1000 ppm, 5000 ppm and 10,000 ppm of the oily saline feedwater, respectively. The 2TNS-PA TFN membrane achieved almost 100% flux recovery for three cycles by hydraulic washing. Full article