Do you know how much effort scientists put into ensuring drinking water safety?

Where does the water we drink every day come from?

Do you know where the water we drink every day comes from? Rivers, lakes, reservoirs, groundwater? No matter where the water comes from, there is a unified concept: drinking water source.

Drinking water sources summarize the water source areas that provide water for urban residents' daily life and public services (such as government agencies, enterprises, institutions, hospitals, schools, catering, tourism, etc.). Based on the number of people supplied with water, decentralized drinking water sources are defined as those with less than 1,000 people supplied through pipelines, while centralized drinking water sources are defined as those with more than 1,000 people supplied.

According to the "Water Law of the People's Republic of China" and the "Water Pollution Prevention and Control Law of the People's Republic of China": All water sources that supply drinking water must be designated as protected areas, and divided into three levels: first-level protected areas, second-level protected areas and quasi-protected areas based on actual conditions.

Identification, transformation and regulation mechanism of natural risk substances in drinking water

Although protected areas have been designated for drinking water sources, natural risk substances are widely present in the environment, affecting the sensory quality of drinking water and human health, and are important targets for global drinking water safety management. Algal substances, natural organic disinfection byproducts, and inorganic anions arsenic and fluorine are typical natural risk substances, which are produced in biogeochemical cycles, are of various types and complex in composition, and are difficult to block from the source through environmental management. The identification and regulation of these substances is a difficult problem for drinking water safety.

The project "Identification, transformation and regulation mechanism of natural source risk substances in drinking water" led by Yang Min, a researcher at the Center for Eco-Environmental Sciences of the Chinese Academy of Sciences, conducted systematic research on key scientific issues such as the identification, formation mechanism and control principle of natural source risk substances in drinking water, and achieved a series of innovative results. It was the first time in the world that cyanobacteria produced teratogenic retinoic acid toxins; it was confirmed that fishy smell is a major odor type of surface water sources in my country, revealing the universality of sulfide fishy odor pollution; it clarified the molecular transformation mechanism of natural organic matter in the coagulation and disinfection process; it was found that nano-Al13 enhanced coagulation can effectively block the formation of disinfection by-products; and it proposed the multi-site complex adsorption principle of composite metal oxides for enhanced arsenic and fluoride removal.

The project's results on algae-derived retinoids were included in the report of the World Conservation Union's Amphibian Specialist Group, raising public awareness of environmental issues related to natural risk substances; the odor results supported the solution to major odor problems in drinking water; the disinfection by-product control results successfully guided the optimization of coagulation processes in drinking water plants with a total capacity of 3.3 million tons/day in many locations. The project won the second prize of the National Natural Science Award in 2017.

Study finds key odorant

The research team conducted a survey on odor identification and in-situ regulation of odor-producing algae in 209 water plants in 55 cities in China and found that more than 80% of surface water sources and nearly half of the water leaving the factory have odors to varying degrees, and the main types of odors are fishy and earthy. Based on sensory gas chromatography, it was found that sulfide substances such as dimethyl trisulfide are the key odorants of the Wuxi odor incident. For example, the team found in long-term research that there are two types of odors in the water source of the Huangpu River, earthy and fishy. Combining comprehensive two-dimensional gas chromatography high-resolution mass spectrometry with sensory gas chromatography, 15 odorants in the water source of the Huangpu River were successfully identified, and the odor activity value ranking and odor reconstruction showed that sulfide substances are the main odorants of fishy odors, and earthy substances can enhance the fishy odor caused by sulfide substances. The national survey found that sulfide substances are the key odorants of fishy odors in water across the country.

2-Methylisoborneol (MIB) in water sources is the main substance that produces earthy musty smells, mainly produced by filamentous cyanobacteria. By establishing an ecological model of algae and testing it, it is proved that under sufficient nutrient conditions, light energy is the main factor driving the change in the structure of algae communities in water bodies, and it is further inferred that odor-producing algae are suitable for growing in the bottom and subsurface layers.

Drinking water safety has always been related to the national economy and people's livelihood. This project discovered new problems of natural source risk substance pollution in drinking water and proposed regulatory principles for strengthening the removal of natural source risk substances. It provided an important theoretical and technical basis for drinking water safety and promoted the development of basic disciplines of environmental science and technology.

(Text: Zhang Yanfang, review expert: Yang Min, researcher at the Center for Eco-Environmental Studies, Chinese Academy of Sciences)

China Association for Science and Technology Department of Science Popularization

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