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Chinese researchers spent a year monitoring the waste water quality at a major high speed rail station in Beijing, and the results worried them. Photo: Xinhua

China’s high-speed trains are overwhelmed by poop, study says

  • Researchers find levels of human waste compounds are hundreds or even thousands of times higher at railway stations than rest of urban sewage system
  • As scientists race to develop new technology to prevent ‘system meltdown’, bacteria-based method might offer answers
Science
The explosive growth of high-speed rail in China has brought a boom in human waste on trains, threatening a meltdown for the railway network’s sewage treatment facilities, according to researchers commissioned by the government to solve the crisis.

“The processing capabilities of waste treatment facilities are declining, some of them already out of service,” said the team led by senior engineer Xin Siyuan with the China State Railway Group in a peer-reviewed paper published in journal Railway Standard Design on May 24.

Xin’s team said that after spending a year closely monitoring the waste water quality at a major high-speed rail station in Beijing, they were deeply worried about the results.

They found the levels of organic compounds indicative of human waste were hundreds or even thousands of times higher in the station than what was typically found elsewhere in the urban sewage system, especially during public holidays.

“The waste water from sealed toilets on trains has a higher content of suspended solids, organic matter (COD), nitrogen, and phosphorus than general domestic waste water,” Xin’s team wrote.

“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.

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Spillover

China is not the only country grappling with the challenge of human waste on trains.

Indian Railways, which had been derided as the world’s “largest open toilet” for its practice of dumping waste straight onto its train tracks, reportedly spent a decade equipping all passenger coaches with bio-toilets that break down human waste.

But unlike Indian passenger trains, which travel at an average speed of about 50km/h, China’s high-speed trains do not have sufficient time or room to allow waste to decompose naturally on board, according to Xin’s team.

According to some studies, an average person produces around 128 grams (0.28lbs) of faeces and 1 litre (0.26 gallons) of urine per day.

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Though not all passengers use the toilet, the total amount of waste produced on a train that operates almost non-stop throughout the day can be significant.

Traditional waste treatment facilities are usually a concrete building with many machines inside. These machines are complex, unstable and easily broken down under the extreme demands of a high-speed rail line, Xin’s team said.

Human waste from trains can cause problems if it spills over into the urban sewage system, the researchers said.

For example, high levels of organic matter and nutrients such as nitrogen and phosphorus in human waste can cause eutrophication if they find their way into bodies of water, leading to excessive algae growth that can deplete oxygen levels in the water and harm aquatic life.

Untreated human waste may also contain harmful pathogens such as bacteria, viruses and parasites that can cause outbreaks of infectious diseases.

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.

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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.

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