“With the increase of the amount of waste water from sealed toilets, the existing sewage treatment facilities can no longer meet the current urban network discharge standards, and it is urgent to establish more complete waste water treatment facilities,” they added.
The team also came up with a possible solution to the problem that uses bacteria to break down human waste more efficiently than existing methods.
Unexpected crisis
China built its first high-speed railway in 2008, a 100km line between Beijing and the northern port city of Tianjin with a top speed of 350km/h (217mph).
In less than 15 years, the length of the country’s high-speed rail network has grown to 42,000km – long enough to circle around the planet.
It is now the most popular mode of transport for intercity travel. The 1,300km line between Shanghai and Beijing, for instance, transports more than 200 million passengers per year, according to official data.
Toilets on China’s high-speed trains are clean, spacious and often equipped with amenities such as electric-powered doors.
When collection tanks on the train are full, the waste is pumped out by machine to be processed at a waste treatment facility, usually located in a railway station.
But the early designers of these facilities apparently underestimated the passenger flow, according to the new study.
China’s high-speed trains do not have sufficient time or room to allow waste to decompose naturally on board, scientists say. Photo: Shutterstock
Promising results
The project team spent more than three months in a laboratory experimenting with a variety of waste samples collected from the railway station to find a cost-effective solution to the rail network’s poop problem, according to the paper.
Their laboratory set-up included numerous reaction chambers, each with different environmental settings, such as varying oxygen levels, to accelerate the breakdown of waste.
They used a combination of different types of microorganisms specially selected for their ability to break down organic matter and remove nitrogen from waste water.
These included ammonia-oxidising bacteria that convert ammonia into nitrite, which is then converted into nitrate by another type of bacteria called nitrite-oxidising bacteria. They also used denitrifying bacteria, which convert nitrate into nitrogen gas, which is then released into the atmosphere.
They found that by growing bacteria on the surface of a plastic sheet and then exposing them to waste water, they could achieve more contact between bacteria and the organic matter in the sewage. In contrast, older methods of biological waste water treatment rely on bacteria suspended in water to break down organic matter.
The team said their method could remove up to 95 per cent of some key organic pollutants such as ammonia nitrogen, even at peak rail traffic periods.
According to the team, some commercial suppliers have developed products based on their method. The most promising products include all-in-one devices that can be installed easily in a railway station.
The new waste treatment devices combine multiple sewage treatment processes into a single unit, allowing for more efficient treatment of waste water. They can be remote-controlled or operated independently by AI, according to the team.
“The device has a small footprint, can be installed underground or above ground, is easy to install and has an attractive appearance,” they added.
South China Morning Post
