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When we turn on the faucet and clear water flows out, behind this is actually the result of the hard work of many researchers and technical personnel.

In this, coagulation technology, as the "first line of defense" to protect our drinking water, its importance is self-evident.

However, coagulation treatment also has its unsolved mysteries and room for optimization.

Generally speaking, coagulation technology mainly uses the hydrolysis of coagulants to make pollutants in the water come close to these hydrolysis products and interact, thus achieving the purpose of removing pollutants.

But in this series of complex processes, people's understanding before was mainly still at the stage of pollutants coming close to hydrolysis products.And for other key aspects of the coagulation process, such as the growth and breakage of flocs, the micro-interactions between organic matter and hydrolysis products, there is still a lack of in-depth understanding.

This is like watching an exciting movie, only focusing on the climax between the protagonist and the antagonist, but ignoring their psychological journey and the final outcome.

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The coagulation process is also like this, each stage has its unique significance and function, and our neglect of these stages undoubtedly limits the performance optimization of the coagulation process in the removal of natural organic matter.

Based on such background and reasons, Researcher Yu Wenzheng and his team from the Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, have carried out a study.

The purpose of this project is to lift the veil of mystery of the first and third stages of the coagulation process, to observe, analyze, and understand every subtle change that occurs in these stages from a microscopic perspective.By investigating the growth and breakage process of flocs, as well as the interactions between organic matter and hydrolysis products, the team aims to address the question: How to break through the existing coagulation mechanism, further improve the efficiency of coagulation processes in removing natural organic matter, and reveal the underlying deep mechanisms.

In summary, the team hopes that through this research, they can gain a more comprehensive and in-depth understanding of the coagulation process, providing a more solid guarantee for drinking water safety or wastewater treatment.

Yu Wenzheng said, "This research, from the determination of the topic to the final success, is a long and challenging process."

From 2009 to 2010, as a visiting doctoral student, he came to University College London.

There, a chance experimental observation sparked his curiosity.During the experiment of floc formation, he found that rapid stirring would cause fluctuations in the online pH data collection.

Later, he received funding as a Marie Curie International Fellow and once again went to Imperial College London in the UK to engage in scientific research.

At that time, in addition to completing the topics in the Marie Curie Fellow program, he was also continuing to explore the flocculation mechanism.

Then, he began to ponder whether this change in pH was related to the exchange of functional groups on the surface of the flocs and hydroxide ions in the water?

This question became the starting point for subsequent research. Later, he increased the concentration of flocs in the solution and avoided adding buffer solutions to ensure that the changes in the concentration of H+ or OH- in the solution could be truly reflected.At the same time, with the help of his former mentor, Yu Wenzheng negotiated with his then current mentor and set up an experimental device at Imperial College London to monitor and record various data in real time.

Later, he finally observed some interesting phenomena: during the flocculation process, in addition to the addition of flocculants causing a sudden change in the pH of the solution at the moment, the pH would not change during the subsequent slow stirring process.

However, if the stirring speed is increased, the pH will gradually decrease. This excited Yu Wenzheng, proving his guess was correct: that is, the functional groups on the surface of the flocs are indeed exchanging with hydroxide ions in the water, leading to changes in pH.

After returning to China, he was determined to delve into the above topic. Yu Wenzheng let two master's students and one direct Ph.D. student in his research group study the impact of different functional groups of small organic molecules on the flocculation microcrystallization process and the mechanism of complexation between the floc surface and representative organic substances.

Through these experiments, the research group gradually revealed the mystery of the flocculation mechanism. Later, they determined the mechanism of adsorption of organic functional groups on the surface of flocs under different structures, providing a new perspective for the development of coagulation theory.Ultimately, the relevant paper was published under the title "Towards a molecular-scale theory for the removal of natural organic matter by coagulation with trivalent metals" in Nature Water[1].

The team's direct Ph.D. student, Liu Mengjie, is the first author, and Yale University Professor Menachem Elimelech and Yu Wenzheng serve as the co-corresponding authors.

During the paper submission process:

The reviewers highly recognized the team's series of experiments in revealing the fate of trivalent metals and their interactions with natural organic matter during the coagulation process.

And they believe that these experiments not only provide an important and interesting supplement to the current coagulation mechanism but also make a significant contribution to the development of coagulation theory.At the same time, the reviewer especially praised the research team for expanding the coagulation theory from the functional group level.

The reviewer not only emphasized the importance of the η-H2O and η-OH functional groups in the aluminum precipitate, and believed that the team revealed the underlying mechanism by which the selectivity of natural organic matter species in the coagulation process is influenced by their functional groups.

In general, this study on coagulation theory helps water treatment scholars and engineers to have a more comprehensive and in-depth understanding of the coagulation process, which can provide a more solid guarantee for the safety of drinking water and the treatment of wastewater.

Imagine, for those busy wastewater treatment plants, in the process of sludge recirculation, the old flocs are broken multiple times, and their adsorption capacity is greatly reduced.

However, with the guidance of this achievement, engineers can cleverly utilize the adsorption potential of aged coagulants, and by adding new coagulants, reconnect the broken flocs and inject new vitality into them.Thus, not only can the adsorption capacity of the floc be maximized, but the irreversible breakage of the floc can also be effectively prevented, making wastewater treatment more efficient and environmentally friendly.

At the same time, this achievement provides important theoretical guidance for the development of new coagulants.

In the laboratory, scientists can conduct in-depth research on the active groups on the surface of coagulation hydrolysis products, and develop more efficient and environmentally friendly coagulants by optimizing the structure and properties of these groups.

These new coagulants will be like "magic weapons" in the field of water treatment, providing strong support for water quality improvement.

In addition, starting from the new perspective of functional groups, the differences in coagulation efficiency of different raw water can be more deeply explored.This implies that in future water treatment practices, engineers can select appropriate coagulants and treatment methods based on the characteristics of the raw water, thereby achieving the best coagulation effect.

The precise policy-making approach will greatly improve the efficiency and effectiveness of water treatment, contributing to the sustainable use of water resources.

Finally, this achievement will also provide new ideas for changing the natural organic substances in the raw water.

Through treatment methods such as pre-oxidation and pre-chlorination, the carboxyl and phenolic groups in dissolved organic matter can be increased, thereby enhancing their affinity for coagulants.

In this way, during the coagulation process, these organic substances will be more easily removed, thereby improving water quality. This method is not only simple and easy to implement but also has significant effects.In the subsequent plans:

Firstly, to address the issue of the coagulation process occurring too quickly, the team plans to employ in-situ real-time tracking technology to capture key moments in the coagulation process.

This technology can observe and record the dynamic changes in the coagulation process in real time, thereby revealing the structure of intermediate hydrolysis products and the reaction mechanism between hydrolysis products and organic matter.

Secondly, to tackle the complexity of natural organic matter, the research group will further delve into the affinity of other functional groups in natural organic matter with flocs.

In addition to hydroxyl, carboxyl, phenolic hydroxyl, and benzene rings, they will also focus on the role of functional groups such as amino and nitro groups in the coagulation process.Through titration experiments and other methods, it will quantify the affinity of these functional groups with the flocculent body, thereby gaining a more comprehensive understanding of the behavior of natural organic matter during the coagulation process.

At the same time, the research team will also focus on resolving the uncertainties in current research, and further delve into the mechanism of the coagulation process and the behavior of natural organic matter in the coagulation process by adopting new technologies and new methods.