MICROPOLLUTANT REMOVAL USING NANOMATERIALENHANCED FARM WASTE

A research team led by faculty at Zayed University (ZU) has demonstrated an environmentally friendly way to remove an industrial dye micropollutant, utilizing nanomaterials and local agricultural waste.

Protecting water supplies from industrial pollution is an ongoing challenge all over the world, with about 80% of wastewater being released back into the water supply without treatment. Even when wastewater is treated before release, some pollutants remain in tiny amounts, as current water treatment technologies do not target them. These ‘micropollutants’ can contribute to health problems for those living downstream, and can even end up back in the water supply.

Industrial dyes are among the major contributors to water pollution, as they persist in the wastewater discharges of many industries, particularly textiles, plastics, paper, and leather. The textile dyeing and treatment industry alone is estimated to be responsible for 17% to 20% of global water pollution. What makes industrial dyes particularly difficult to remove from wastewater is that dyes are deliberately designed to be resistant to fading and removal. When dye-containing wastewater is released into the environment, it not only discolors waterways, it can also harm plant and animal life, and even cause cancer, skin, eye, and kidney disorders, and genetic mutations in humans.

Dr. Jibran Iqbal, Associate Professor of Chemistry at the College of Natural and Health Sciences at ZU, partnered with Dr. Fares Howari, Dean of ZU’s College of Natural Health Sciences, to develop an innovative way to remove a particularly harmful industrial dye known as ‘Congo red’ from water. Working with other

Associate Professor of Chemistry at the College of Natural and Health Sciences, Zayed University researchers from the UAE, Pakistan, and Australia, they leveraged nanomaterials to produce a low-cost and efficient way to remove the dye pollutant.

“Water contamination by micropollutants is a global issue of great concern and requires special attention. The Congo red industrial dye is one of the major micropollutants contributing to water pollution. Dyecontaining effluents have to be efficiently treated before they are discharged into water bodies or the environment, which requires the development of more effective treatment processes,” said Dr. Iqbal.

Invented in the 1880s, Congo red dye has been widely used in the textiles and paper industries, as well as in biomedical research and diagnostics. But in the intervening decades, the dye was discovered to be toxic and can damage human health, causing cancer, lung and kidney infections, and gene mutation. Banning or reducing the use of Congo red is not enough, however, as the dye is non-biodegradable, meaning it remains in the environment for long periods of time as a micropollutant.

The current methods for removing Congo red from industrial wastewater, which include electrochemical treatment, photochemical degradation, membrane separation, bioremediation, and ion- exchange, are high-cost processes with their own functional limitations and trade-offs. Developing a less costly, more effective, and less environmentally taxing method could support increased and improved removal of Congo red from wastewater.

Left to right: Dr. Jibran Iqbal and Dr. Fares Howari

The ZU-led research team focused their Congo red remediation solution on biochar made from local agricultural waste, which they enhanced with nanotechnology. Biochar is produced when biological material is subjected to high temperature in a limited oxygen environment. This transforms the material into a carbonrich solid, like charcoal. Biochar is cheap, renewable, and widely available, as well as having valuable physical properties, like being porous and reactive. For this project, the researchers made biochar from waste date palm leaves collected from local date palm fields.

“The advantage of using natural palm waste is that it is abundantly available in the UAE and is also an environmentally friendly material. By using date palm waste in this way, we are effectively recycling it for a beneficial use, rather than just discarding it. The specific material characteristics of date palm biochar make it a very efficient adsorbent to remove pollutants from aqueous solutions,” Dr Iqbal explained.

The date palm leaf biochar was infused with nanoparticle zero-valent manganese (nZVMn) to enhance its ability to adsorb and catalytically degrade pollutants. In adsorption, the targeted molecules, atoms, or ions are held to the surface of the material to enable their collection or capture. In catalysis, a catalyst is used to speed up or enable a chemical transformation. Zerovalent metals have valuable properties, like binding and catalysis, which are further enhanced when shrunk to the nanoparticle size. Engineering nanoscale zero-valent metals is an emerging science that is being explored for environmental remediation and other industrial processes.

Materials behave differently at the nanoscale, which refers to 100 nanometers or smaller. The small size effect of nanomaterials makes them more catalytic and highly sensitive. Because nanomaterials have more surface area, they are also more adsorptive and have higher reaction efficiency. The quantum size effect experienced by nanomaterials also improves their optical and electronic properties. These unique characteristics have lent themselves to the advancement of nanomaterials technology. The adsorptive and catalytic characteristics of metal nanoparticles are further enhanced when they are zero-valent. Valence, or valency, of an element is the measure of its combining capacity with other atoms when it forms chemical compounds or molecules. Metal ions can be subjected to a reduction process that renders them zero-valent.

“The recycling, adsorptive, and catalytic properties of biochar were enhanced by impregnating it with mesoporous nanozerovalent manganese. The resulting composite material exhibited excellent characteristics, such as high surface area, thermal stability, small size, crystallinity, and recovery. The prepared material showed good performance as an adsorbent as well as a catalyst and caused significant removal of pollutant from water,” Dr. Iqbal said.

The researchers tested the efficacy of their basic date palm biochar, the nZVMn embedded biochar, and nZVMn biochar in the presence of hydrogen peroxide, to see how well they removed Congo red from water. They specifically measured their adsorptive and oxidative removal of the dye. After 120 minutes, the biochar alone removed about 46.5% of the Congo red, while the nZVMn biochar removed 77%, and the hydrogen peroxide coupled nZVMn biochar removed 95%, showing that the addition of hydrogen peroxide to the process enhanced the oxidative removal of the Congo red.

The research team then investigated the efficacy of the two forms of the date palm biochar material – basic and nVZMn embedded – over multiple use cycles. They found that the embedded biochar could be washed, dried, and reused seven times while still removing up to 64% of the Congo red. In comparison, the basic biochar was able to retain efficacy up to only four cycles.

“Our project proved the possibility of converting abundantly available date palm waste into low-cost engineered biochar for wastewater treatment. The results showed promising insights that serve as milestones in the research into low-cost, environment friendly biochar-based water purification technologies,” Dr. Iqbal stated. He and his collaborators, who included Noor Shah, Murtaza Sayed, Nabeel Khan Niazi, Muhammad Imran, Javed Ali Khan, Zia ul Haq Khan, Aseel Gamal Suliman Hussein, and Kyriaki Polychronopoulou, published a paper on their research in the Journal of Hazardous Materials.

Having demonstrated how the intrinsic water pollution-mitigation value of date palm biochar can be enhanced by embedding it with zero-valent metal nanoparticles in the presence of hydrogen peroxide, the research team believes they can use the enhanced biochar to remove even more classes of pollutants. They now intend to explore further the integration of date palm biochar with nanomaterials to remove other wastewater contaminants.

“The next step for this area of research is to explore the ability of nanomaterialenhanced date palm biochar to remove many other emerging organic contaminants – like pharmaceuticals and personal care products – from wastewater, and make it applicable for large-scale remediation programs in the UAE,” Dr. Iqbal concluded.