Team:USTC/Integrated HP

This year, our team has been devoted to treat azo dye pollution with a more efficient and environmentally friendly method. We have attached great importance to integrated human practices, and in return, our human practices have been inspiring and navigating us all along the way. Here, we are going to present the whole process revealing not only what we have achieved but also how our investigations influenced our work.

Before our trips

Azo dyes are a kind of chemicals that exist in polluted water and are especially hard to tackle. Owing to its high stability, regular approaches to degrading them are either too expensive or not efficient enough. As a result, these deleterious chemicals often remain in water, causing continuous harm to the environment as well as living creatures including human beings. Among all the industries that produce wastewater containing azo dyes, the dyeing and printing industry obviously accounts for a substantial part.

We are excited to notice that such environmental problems have aroused more and more attention throughout China. The government is also taking measures to fight against water pollution. However, there still seems to be a long way to go. We hold the belief that synthetic biology may be the key.

At the first place, we were confronted with the situation where detailed information was insufficient. We decided to degrade the azo dye molecules by the aid of S. oneidensis MR-1, but we did not know much about what kinds of dyes were utilized in the actual dyeing industry. Neither were we certain about the feasibility of our design. Therefore, we planned to visit a dyeing factory.

A visit to a dyeing factory

On August 16th, 2019, we set off to Wujiang Sanlian Printing & Dyeing Factory in Suzhou, Jiangsu province. The factory manager Mr. Xu passionately showed us around the dyeing workshops and reagent preparation rooms.

In the dyeing workshops, he explained to us the whole dyeing process and techniques being used to improve dyeing efficiency, thus reducing the usage of dyes. In the reagent preparation rooms, we were surprised to see all kinds of dye powders varying in colors. According to the manager’s introduction, azo dyes can be divided into different types that are applicable to different pH and dyeing materials. His words remind us that we should pay attention to the conditions when we deal with different dyes.

We also inquired the manager about the treatment of effluent. He told us that nearly all the wastewater was gathered by sewage pipes, transported to a water treatment plant and finally received treatment there. In other words, the dyeing factory itself was, to our disappointment, barely responsible for water treatment.

Although we did not see the treatment processes in this trip, we still gained a clearer understanding of water pollution caused by azo dyes and of its source. We also received the manager’s encouragement as well as valuable advice, which motivated us to start out on our project.

Fig 1. Our group members.

Fig 2. Dyeing machines.

Fig 3. We have a close look at the dyeing process.

Fig 4. Dyed cloth with different colors.

Fig 5. The manager is explaining to us in the reagent preparation room.

Fig 6. Sewage pipes.

A visit to a water treatment plant

Based on the knowledge we had gained from our last trip, we found it necessary to visit a water treatment plant and find out more.

We went to Anhui Yiyuan Environmental Protection and Technology Co., Ltd. in Anqing, Anhui province on September 8th, 2019. This company specializes in treating effluent of dyeing and printing industry.

We first looked at the flow chart of wastewater treatment as shown below.

Fig 7. The flow chart of wastewater treatment.

The treatment of wastewater involves physical, chemical and microbiological methods. We were most curious about the microbiological part. The technician, Mr. Zhang, who conducted us around the factory made a description of the bacteria in the tanks. The bacteria are immobilized on tree-shaped devices and ropes which are suspended in the flowing water. Such appliances are used in the hydrolytic acidification tank and contact oxidation tank to support microorganism-facilitated reactions. Since there have already been well-established facilities intended for microorganisms, we do not need to design our own hardware.

The present facilities also provided us with inspirations about biosafety. If our bacteria were to be put into practical use, biosafety should be of the greatest concern. The characteristics of our bacteria and the present facilities together determine the anerobic condition, which means that the tank would be covered completely, creating a dark environment. The suicide switch controlled by light would then be applicable: if bacteria leaked into the outside environment and got exposed to blue light, the suicide switch would be turned on and kill the bacteria.

We found out that the contact oxidation tank was largely dependent on ozone, rather than microorganisms. Wastewater contains a great variety of chemicals, such as carbohydrates, lipids and azo dye molecules. The previous steps mainly focus on degradation of molecules like carbohydrates and lipids, before the water flows into the contact oxidation tank, where ozone breaks down other molecules including azo dyes through oxidation. However, the drawback is that generating ozone consumes a lot of electricity. It was astonishing to learn from the technician that this single step took up to about one third of expenditure of the whole factory. If our microorganisms can help improve the efficiency and lower the cost of azo dye degradation, it would be a good substitute for ozone.

Fig 8. Our group members.

Fig 9. The regulating tank.

Fig 10. The technician explains to us at the primary settling tank.

Fig 11. The contact oxidation tank with a cover on it.

Fig 12. Ozone generating devices.

Fig 13. Ozone tanks.