Ural Federal University: Lychee Peel Powder Can Remove Persistent Dye from Wastewater

The international team of scientists, which includes chemists from the Ural Federal University, found out that chemically modified lychee peel eliminates a very persistent red dye from wastewater. The researchers have developed a new method that can be used to clean wastewater near textile production facilities in an environmentally friendly and cheap way. By doing so, it can prevent disease in humans and save animals, fish and birds that interact with dyed water. It will also help make the world’s dirtiest rivers cleaner: the Buringanga River in Bangladesh, the Ganges in India, and the Chintarum in Indonesia, for example. A description of the new method and the results of the experiments were published in the Journal of Molecular Liquids.

“Red dyes emitted in various industries such as textiles, cosmetics, leather, food and plastic are dangerous environmental pollutants. From 20 to 40% of persistent dyes remain in wastewater and cause a critical increase in its acidity, alkalinity. The key factor here is the nature of these dyes. They contribute to increased deposition of calcium salts in organs, are considered highly toxic and pose a serious threat to humans, causing various cancers and mutagenic phenomena at cellular and molecular levels,” explains Grigory Zyryanov, Professor of the Department of Organic and Biomolecular Chemistry at the Ural Federal University.

For example, according to Hort Innovation, a research corporation, global production of lychee is 1.8-2.55 million tons per year. The edible part is the juicy pulp. The peel, along with the seeds, is usually discarded. The peel makes up about 15% of the weight of the fruit, which is 270-383 thousand tons of the total production. Today, a significant amount of lychee waste is not disposed of in any way. Since the inedible part of the fruit can be recycled for wastewater treatment, there will be less trash in the form of peels – a true zero-waste production.

Lychee peels contain special functional groups that are capable of interacting with particles of a given dye, the scientists explain. The method is based on the adsorption process. This is similar to the electrified balloon: if you bring it into a dusty room, dust will immediately begin to collect on it. Likewise, lychee rind: with the substances it contains, and in combination with a substance that enhances its properties, when immersed in sewage water, it collects on itself particles of a persistent red dye.

Compared to other cleaning methods, this new method is much more efficient because of the low energy consumption and minimal operating costs of the entire process. Also, the modified peel almost completely removes the dye and produces no dangerous byproducts or sludge. In addition, the lychee peel is extremely durable in service: after five regeneration cycles, the converted powder retains its previous adsorption efficiency.

To be used as a sorbent, the lychee peel was cleaned, dried, and ground to a powdery state. After that, glycidyl trimethylammonium chloride was used to modify the surface of the rinds, which allowed the introduction of additional receptor groups. The lychee peel thus modified exhibited sorption properties.

The scientists plan to continue the research. Chemists are also considering other previously unused food waste as sorbents for treating wastewater from various dyes.