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Getting the most out of waste to make sure it's not rubbish
Article type: Redistributed 2020-06-17 Font Size:[ S M L ] [Print] [Close]

By Cao Chen

With more Chinese cities slated to implement compulsory garbage sorting regulations, teams from the China-UK Low Carbon College at Shanghai Jiao Tong University have been working to devise more efficient means of accomplishing this task through the use of high-end technology.

Among the ongoing projects in the college is a robot that can sort dry waste.

According to the team behind this project, the machine can identify a piece of dry waste before placing it in its respective container. The device currently boasts a 90 percent accuracy rating and can sort up to 5,400 pieces of waste per hour.

"Workers involved in manual sorting of unseparated domestic waste are exposed to unhygienic environments," says Li Jia, the project leader and associate professor at the college.

"The work also poses risks to workers' safety as there are sometimes items such as sharp metal pieces or broken glass that could hurt them."

Furthermore, it's getting more difficult to hire such workers given the harsh working conditions, Li adds.

"Robots would be useful for such repetitive and arduous tasks. Two robots operating for 24 hours a day can handle the workload of 54 workers, and with a higher efficiency," he says.

"Using robots will also improve the speed and quality of recycled waste re-entering the production process as valuable raw materials, thereby reducing the pollution associated with the manufacture of new materials."

Li notes that there is a lack of waste-sorting equipment in the domestic market, and such products developed by other countries are prohibitively expensive-a single unit could cost up to 10 million yuan ($1.4 million). Maintenance costs are high as well.

Equipped with three kinds of cutting-edge sensors and other technologies like contour identification, the machine can identify the color, shape and texture of an object, as well as what it is made of. An algorithm also enables the robotic arm to determine the most efficient way to fetch items.

According to Li, the team will cooperate with factories and companies to conduct performance assessments on the robot.

"The components of garbage are different in every city and neighborhood, and these varying elements will affect the performance of the machine," he says.

"The robots need to be trained to work in the real environment."

The college has also been cooperating with the National University of Singapore to create a system that can turn kitchen waste into electricity and heat.

Kitchen waste is conventionally collected and shipped by trucks to a center for centralized treatment. But the long-distance transportation creates problems, such as pollution from vehicle emissions and garbage odors.

"These issues could be solved by the wet waste treatment system we are developing," says Zhang Jingxin, the project leader and associate professor at the college. "It is a relatively compact 5.8-meter-long, 2.3-meter-wide and 2.3-meter-high mobile container that can fit in any neighborhood."

The core of the system is an anaerobic tank. Kitchen waste is ground before being pumped into the tank where it is broken down into biogas after coming into contact with anaerobic microbes. The system then converts the biogas into electricity and heat.

"The electricity can be directly exported and used for mobile phone charging, promoting resource utilization," says Zhang.

"The composition of kitchen waste affects the amount of power generated. The higher the hydrocarbon, protein and fat content in the waste, the more biogas is produced and the more electricity is generated."

The system is presently on trial at both the National University of Singapore and the China-UK Low Carbon College. The results from Singapore show that the energy generated by 40 kilograms of kitchen waste can charge up to 1,000 mobile phones.

Another project in the college is focused on the treatment of a specific type of wet waste-crustaceans.

Around 8 to 10 million tons of crustacean waste is generated globally, most of which is directly dumped in landfills, according to Chen Xi, assistant professor at the college.

"Such garbage releases large amounts of carbon dioxides and nitrogen oxides, contributing to the greenhouse effect," she says.

Chen explains the focus on this specific waste type, saying that the main components of crustaceans are natural renewable resources, such as calcium carbonate that can be used as building materials and proteins that can be used as animal feeds.

"Another component, chitin, is a valuable resource with huge but underestimated potential to produce useful nitrogen-containing chemicals, such as ethanolamine which absorbs carbon dioxide, and Proximicin A, an anticancer drug precursor," she says.

"The traditional approach to extracting chitin from shrimp and crab shells has already been developed. However, the current process uses corrosive acids and alkalis, which in turn produce acid and alkaline industrial sewage, causing environmental pollution and inducing high costs."

According to Chen, the technology used in the project is inspired by the formation of stalactites in nature, where calcium carbonate in stalactites is dissolved after coming into contact with water and carbon dioxide.

Meanwhile, the proteins in the shell are removed by high temperature water.

Using the new method can extract chitin with a purity of up to 90 percent.

Lab data shows that this approach reduces carbon emissions by about 80 percent and costs by half when compared with the traditional method.

"We will do more pilot tests and cooperate with seafood treatment plants prior to the industrialization phase," she says.

She adds that government support will also be necessary in the future to instruct people to separately utilize crustacean waste from other kinds of wet garbage.

Source:China Daily