Hydrophobic organic pollutants bond strongly to sediments, in this way they can remain in water and soils long after the original source has been removed. A recent publication in Environmental Science & Technology now reports a selective separation catalysis membrane which overcomes the limitations of sulphate advanced oxidation processes, thus harnessing the processes for organic pollutant removal in an environmentally friendly way .

The sulphate radical advanced oxidation process is efficient, easy to implement and capable of oxidizing in a wide pH range.  But it has limited practical application, mainly because of the toxic byproducts due to excessive oxidant salts and oxidative sulphate product which pollutes the contacting water.  [1] Coupling the oxidation chemistry with catalyst membranes could lead to safer implementation in wastewater and soil treatment . [2]

Catalytic membrane based processes have attracted substantial interest because they are capable of combining the functions of reaction and separation processes in one step. The catalysts anchored in the membrane improve the reagents sorption and the membrane excludes other compounds from interfering. [3] However, the membrane pores are often blocked by impurities in water and soil washing solution, such as natural organic matter, resulting in a steep decline of catalytic activity. The possible leaching of oxides and byproducts into the contact water also constrains its utilization in flow-through systems. [4]

Baoliang Chen and his group from Zhejiang University designed a new selective separation catalysis membrane to remove the organic pollutants from water and soil.  The membrane overcomes the limitations of persulfate oxidation processes by also removing toxic by-products which would otherwise harm aquatic life. The membrane is composed of four layers: selective, dense, catalyst and nonwoven layers. The first selective layer uses water-repellent polydimethylsiloxane as a barrier, which extracts the hydrophobic pollutants and excludes the natural organic matter and water molecules as well

The catalyst, a cobalt-coated nitrogen-doped porous carbon material, is constructed beneath the selective and dense layer, which protects the catalysts form the natural organic matter interference and increases the accessibility of the catalyst to the pollutants. In this way, the device achieved highly efficient reaction because of the concentrated reactants in the catalyst layer.  The three layers are supported on the non-woven fabric layer. Compared to the catalyst in powder form, the new catalytic membrane system achieved 80% removal of phenol, a typical hydrophobic organic compound, with more than 40% reduction in the peroxymonosulphate dosage and 97.8% reduction in catalyst dosage. The new device rejected 91.43% natural organic matter, humic acid in this case, for 100 hours – successfully protecting the sulphate radical advanced oxidation processes from the interference of natural organic matter. Meanwhile, toxic byproducts were isolated within this sequenced layer structure, thus avoiding pollution of the contacting water.

The new selective separation catalysis membrane demonstrates promising applications in environmental remediation, as it provides an approach to remove the organic pollutant that is cost-effective with less damage to the environment as a result of reduced toxic catalytic by-products. The researchers describe their findings as a new “strategy to integrate membrane technology with catalysts” for safe and efficient hydrophobic organic pollutant removal.

The original article can be found here:

Qiu, Z., Xiao, X., Yu, W., Zhu, X., Chu, C. and Chen, B., 2022. Selective Separation Catalysis Membrane for Highly Efficient Water and Soil Decontamination via a Persulfate-Based Advanced Oxidation Process. Environmental Science & Technology. DOI: https://doi.org/10.1021/acs.est.1c06721

References:

[1] Xia, X., Zhu, F., Li, J., Yang, H., Wei, L., Li, Q., Jiang, J., Zhang, G. and Zhao, Q., 2020. A review study on sulfate-radical-based advanced oxidation processes for domestic/industrial wastewater treatment: degradation, efficiency, and mechanism. Frontiers in Chemistry, p.1092.

DOI: https://doi.org/10.3389/fchem.2020.592056

[2] Duan, X., Yang, S., Wacławek, S., Fang, G., Xiao, R. and Dionysiou, D.D., 2020. Limitations and prospects of sulfate-radical based advanced oxidation processes. Journal of Environmental Chemical Engineering, 8(4), p.103849.

DOI: https://doi.org/10.1016/j.jece.2020.103849

[3] Ozdemir, S.S., Buonomenna, M.G. and Drioli, E., 2006. Catalytic polymeric membranes: Preparation and application. Applied Catalysis A: General, 307(2), pp.167-183.

DOI: https://doi.org/10.1016/j.apcata.2006.03.058

[4] Zhang, X., Zhang, L., Li, Z., Jiang, Z., Zheng, Q., Lin, B. and Pan, B., 2017. Rational design of antifouling polymeric nanocomposite for sustainable fluoride removal from NOM-rich water. Environmental Science & Technology, 51(22), pp.13363-13371.

DOI: https://doi.org/10.1021/acs.est.7b04164

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