Mainland scientists have developed a "bioweapon" that can wipe out the notorious bad smell in public toilets.
Up to 75 per cent of the odour can be removed, with the rest suppressed by a natural, pleasant fragrance, according to researchers with the Chinese Academy of Sciences.
The magic is mainly done by bacteria in the Lactobacillus family, which is used in the production of yogurt, cheese, beer and chocolate.
Lactobacillus feeds on human waste, releasing lactic acid that eliminates the growth of most odour-making bacteria.
The technology can be applied in either liquid or power form, and it is cheap. A half-litre bottle costs about 20 yuan (HK$25) and it can be used to treat several toilets as the bacteria grows rapidly on waste.
The "smell-free toilet" study was highlighted on the academy's website last month as offering an "ultimate" cure to an "urgent" national issue.
Dr Yan Zhiying, a bacteriologist with the academy's Chengdu Institute of Biology and lead scientist on the project, said tourists in Sichuan province would be the first to benefit from the technology.
The province is home to numerous tourist attractions, including the Jiuzhai Valley National Park, which plans to introduce the smell-killing germs to its public toilets.
"They will get a refreshing experience," Yan said.
The poor sanitation in most public toilets on the mainland has been a nightmare for many people at home and from abroad.
Many toilets in less developed areas of the mainland do not flush and waste can be left for months, if not years.
To further reduce odour, the team has also researched introducing yeast, which feeds on nitrogen, and bacteria that can produce a pleasant aroma.
The research team spent years isolating micro-organisms from human and pig intestines, where conditions were regarded as more or less similar to a waste pit.
More than 100 possible candidates emerged, all of which were studied and tested in the real world.
Yan said that the technology could be applied to any place with smelly organic waste, such as animal farms or urban dump yards. A major landfill site in Guangzhou had already contacted the team about using the technology.
If the technology is applied nationwide, the institute is able to produce 1,200 tonnes of the powder a year.
But the method only works in certain conditions. For instance, the bacteria thrives in temperatures of 26 degrees Celsius or above, so it cannot be used in unheated toilets in winter.
The micro-organisms also needed food to survive, Yan said.
"The effect will be limited in a flush toilet. The more waste in a toilet, the better the result," he said.