Oil/water separation, especially emulsified oil/water mixture separation, has become a widespread concern because of the severe fouling problem caused by the easy adsorption of oil droplets onto the surfaces of filtration membranes. Many strategies have been employed to eliminate the fouling problem, but it remains a challenge and impedes the development of membrane technology. In this short review, we discuss the recent development of membrane technology for emulsified oil/water separation. As shown in the image, in addition to polymer- and ceramic-dominated traditional membranes, nanomaterial-based membranes have recently demonstrated their superiority and have achieved high performance.

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Recent progress in developing advanced membranes for emulsified oil/water separation

Recently, the enzymatic approach has attracted much interest in the decolorization/degradation of textile and other industrially important dyes from wastewater as an alternative strategy to conventional chemical, physical and biological treatments, which pose serious limitations. Enzymatic treatment is very useful due to the action of enzymes on pollutants even when they are present in very dilute solutions and recalcitrant to the action of various microbes participating in the degradation of dyes. The potential of the enzymes (peroxidases, manganese peroxidases, lignin peroxidases, laccases, microperoxidase-11, polyphenol oxidases, and azoreductases) has been exploited in the decolorization and degradation of dyes. Some of the recalcitrant dyes were not degraded/decolorized in the presence of such enzymes. The addition of certain redox mediators enhanced the range of substrates and efficiency of degradation of the recalcitrant compounds. Several redox mediators have been reported in the literature, but very few of them are frequently used (e.g., 1-hydroxybenzotriazole, veratryl alcohol, violuric acid, 2-methoxy-phenothiazone). Soluble enzymes cannot be exploited at the large scale due to limitations such as stability and reusability. Therefore, the use of immobilized enzymes has significant advantages over soluble enzymes. In the near future, technology based on the enzymatic treatment of dyes present in the industrial effluents/wastewater will play a vital role. Treatment of wastewater on a large scale will also be possible by using reactors containing immobilized enzymes.

Potential Applications of the Oxidoreductive Enzymes in the Decolorization and Detoxification of Textile and Other Synthetic Dyes from Polluted Water: A Review

Oil–water separation is a worldwide challenge because of increasingly oily wastewater, as well as frequent oil spill accidents. We report in this work the fabrication of a zwitterionic polyelectrolyte brush (poly(3-(N-2-methacryloxyethyl-N,N-dimethyl) ammonatopropanesultone), abbreviated as PMAPS)-grafted poly(vinylidene fluoride) (PMAPS-g-PVDF) membrane via a surface-initiated atom transfer radical polymerization (SI-ATRP) technique for separating oil from water. By tuning polymerization time, a superhydrophilic and underwater superoleophobic PMAPS-g-PVDF membrane was successfully prepared. The membrane can be applied for thoroughly separating dispersed oil from water with ultrahigh separation efficiency >99.999% in terms of rejection coefficient. The oil contents after one-time separation of a selection of oil–water mixtures are all less than 10 ppm and some of them are even lower than 2 ppm. These values are much lower than the standard minimum requirements of the international regulations for wastewater discharging. The oil-adhesion force between an oil droplet and the membrane surface was measured to be less than 1 μN. Due to the ultralow oil adhesion, the membrane exhibits an excellent antifouling property to oil and is easily recyclable.

A novel zwitterionic polyelectrolyte grafted PVDF membrane for thoroughly separating oil from water with ultrahigh efficiency

An overview of oil-water separation using gas flotation systems.

Dyes used in the coloration of textiles, paper, and other products are highly visible, sometimes toxic, and sometimes resistant to biological breakdown; thus it is important to minimize their release into aqueous environments. This review article considers how biosorption of dyes onto cellulose-related materials has the potential to address such concerns. Numerous publications have described how a variety of biomass-derived substrates can be used to absorb different classes of dyestuff from dilute aqueous solutions. Progress also has been achieved in understanding the thermodynamics, kinetics, and chemical factors that control the uptake of dyes. Important questions remain to be more fully investigated, such as those involving the full life-cycle of cellulosic substrates that are used for the collection of dyes. Also, more work needs to be done in order to establish whether biosorption should be implemented as a separate unit operation, or whether it ought to be integrated with other water treatment technologies, including the enzymatic breakdown of chromophores.

https://ojs.cnr.ncsu.edu/index.php/BioRes/article/download/BioRes_06_2_2161_Hubbe_HD_Removal_Pollutants_Review_Pt1_Metals/1901

A.E. James

Papers

Destabilisation of oil-water emulsions and separation by dissolved air flotation.

The development of a laboratory method for quantifying the bioelimination of anionic, water soluble dyes by a biomass