Who makes the water smell bad? Find the culprits of the water odor

Water is the source of life. According to the "Dietary Guidelines for Chinese Residents", each person should drink 1500-1700 ml of water every day. Where does drinking water come from? In my country, most drinking water comes from rivers, lakes, groundwater, etc. Many water sources are in nature.

In the natural environment, there are widespread risk substances in drinking water. For example, lakes may contain bacteria, green algae and other microorganisms. In order to ensure the safety of drinking water, water will be disinfected before being delivered to thousands of households. However, during the disinfection process, certain substances in the water may also react with the disinfectant to produce some disinfection by-products that endanger human health.

Yang Min, a researcher at the Eco-Environmental Research Center of the Chinese Academy of Sciences, has led a team to conduct long-term research on water quality risks. Their research results, "Identification, transformation and regulation mechanism of natural risk substances in drinking water", won the second prize of the National Natural Science Award in 2017.

Finding the culprit

What exactly causes the smell in the water? This question is difficult to answer. Humans are very sensitive to odors, but it is difficult to describe them specifically, and it is also difficult to match odors with specific chemicals. Sometimes there is only one smell, but in fact there may be dozens or even hundreds of substances causing the odor. In terms of odor identification and control strategies, Yang Min's team came up with a solution - sensory gas chromatography. They used a gas chromatograph-mass spectrometer to separate gases mixed with various substances, extract a single substance, and then divide the gas into two paths, one directly for human noses to smell, and the other for a mass spectrometer to identify what substance it is. In this way, the smell can be matched with a single substance to find out what the odor is made of.

After analysis, Yang Min's team found that the odor in Wuxi's drinking water was mainly caused by "sulfide" substances. After that, Yang Min's team also investigated 209 water plants in 55 cities across the country and found that "sulfide" substances were the main cause of the fishy odor in water everywhere. They proposed a systematic drinking water odor evaluation and substance identification method, providing a powerful tool for the safe management of drinking water.

Removing pollutants and developing new materials

In response to the problems of excessive arsenic and fluoride, Yang Min's team has developed a series of new materials that can effectively absorb arsenic and fluoride. Based on past research, they have developed "large-flux electrodialysis technology" that can remove fluoride and calcium from water cheaply and efficiently.

In addition to toxic substances such as arsenic and fluorine, disinfection by-products in drinking water may also endanger human health. Yang Min's team believes that instead of removing disinfection by-products after they appear, it is better to find a way to make the disinfection process safer and produce fewer disinfection by-products. In order to achieve this goal, Yang Min's team used ultra-high resolution mass spectrometry to figure out which natural organic matter in the water will react with chlorine in the disinfectant to produce disinfection by-products during the disinfection process. They found that this type of key substance is mainly natural organic molecules with strong electronegativity. Water plants can use high-efficiency coagulants to intervene in the disinfection treatment process. It provides important theoretical and technical support for drinking water safety.

Text: Fan Kexin, Imperial College London

Expert: Zhu Yehua, deputy editor of Science and Technology Herald and PhD of Tsinghua University

China Association for Science and Technology Department of Science Popularization

Xinhuanet

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