Cleaning oil from wastewater using nanoparticles

There may be a smarter way to clean oil from wastewater. A technique using a biocompatible ‘nanosorbent’ that adsorbs oil inside its porous structure is reported on in Applied Materials Today in an article by Yogendra Mishra at Mads Clausen Institute, NanoSYD University of Southern Denmark, with colleagues at Amity University in India and the Indian Institute of Technology, Kharagpur.

Mishra explains that the petroleum industry's wastewater discharge poses significant environmental challenges worldwide. The oily component of the discharge contains a cocktail of hazardous chemicals, including some particularly concerning ones called aromatic hydrocarbons. One common aromatic compound, benzene, brings well-established risks of causing cancer.

“The release of oily wastewater to the environment prior to any pre-treatment or purification can have catastrophic consequences on human health and ecosystems,” Mishra says. “Many adsorbents, including sponge, mesh and fibres, and also efficient nanoadsorbents, have been reported for wastewater oil removal, but there are problems with their lack of biocompatibility and recovery methods.”

The dangers of the problem and the limitations of existing methods led Mishra’s quest to look for a more effective solution.

The key advantages of the new nanomaterial are its simple production method, its biocompatibility, its exceptional ability to selectively absorb chemicals in oil from water and the simple recovery method using its magnetism. Petrol, diesel and kerosene, for example, are all absorbed very effectively.

The production method begins by making a material called zinc-oxide tetrapod, which forms an extended but flexible 3D network permeated with many pores that create a very high internal surface area to entrap adsorbed oil. This initial network is also very stable and strong.

A second step adds in the magnetic and excellent specific oil-absorbing properties of nanorods constructed from iron oxide. This material is deposited on the internal surfaces of the pores created in the first step.

Finally, the fine structure of the composite particles is appropriately modified using the polydimethylsiloxane (PDMS) polymer. This creates a ‘superoleophilic’ (extremely oil attracting) and ‘superhydrophobic’ (extremely water repelling) final product.

The researchers examined the external and internal 3D structure of the material in fine detail using X-ray diffraction analysis and scanning electron microscopy. They also undertook detailed analysis of the magnetic characteristics using a superconducting quantum interference device.

The material is not intended to be used on large scale oil spills. It is designed to be used within a petrochemical plant to treat wastewater before it is discharged into the environment.

The efficiency in that application was tested using various mixtures of diesel oil in water, which were shaken with the nanosorbent for around 50 minutes. An external magnetic field then separated the oil-laden nanosorbent, which could then be cleaned of oil by being washed in ethanol. The researchers anticipate their material could be reused through many cycles.

The initial proof-of-concept trials have been small scale, but the team now plan to scale up for pilot-scale trials using 1000 litres of contaminated water.

Article details: 

Mishra, Y. K. et al.: “Efficient oil removal from wastewater based on polymer coated superhydrophobic tetrapodal magnetic nanocomposite adsorbent,” Applied Materials Today (2019)