For the uninitiated, entering a public lavatory in China can be a horrifying experience.

In smaller cities, or the countryside, the sight of an open trench filled with excrement, coupled with a suffocating stench of sulphur and ammonia, is often enough to send even the bravest tourist whimpering back to their hotel.

In the 1990s, a third of all complaints to tourism officials in Beijing concerned the design, and odour, of public lavatories.

China has battled stinky loos for at least 2,000 years. In the Kingdom of Wei (220-265AD), visitors to the palace bathrooms would find boxes of dates to stuff up their noses and ward off unpleasant odours.

However, both flushing lavatories and toilet paper were invented in China, although only initially for the use of the emperor.

Today, however, Chinese scientists have claimed victory in their battle to improve public rest rooms, unveiling a bacterial spray that can, they say, almost eliminate the smell of putrefaction.

First, a set of six strains of bacteria work to break down the odorous compounds and then a perfume made from orange peel lightly scents the air.

The "smell-free lavatory" study from the Chinese Academy of Science was declared the "ultimate" cure to an "urgent" national issue.

"Five scientists have worked on this from 2011 to the beginning of this year," said Dr Yan Zhiying, a bacteriologist with the academy's Chengdu Institute of Biology, adding that they had spent ￡140,000 on the project.

"Some local government officials here visited a sewage plant and saw that the treatment technology had come from Japan. They wanted a home-grown solution so they asked us to work on it," he added.

"We extracted bacteria from all type of excrement, human, pig, chicken and duck, and we tested our compounds one by one," he said.

"The smells coming out of public lavatories, or cesspits, or rubbish tips, are made up of more than 160 different compounds," he explained, adding that their bacteria, including a strain from the lactobacillus, saccharomycetes and actinomycetes families, can convert and absorb many of them.

He boasted that the Chinese formula, which costs around ￡5 per litre, has no side effects and can be used to fend off the stench of any type of biological decomposition.

More recently, Beijing has waged a war to improve conditions in public lavatories, first introducing a star-rating and then, two years ago, drafting a rule that no more than two flies should be present in any of the city's facilities at the same time.

对外国人来说，中国的公共厕所简直是一场噩梦。

上世纪九十年代，北京旅游管理处收到的三分之一的投诉都跟公共厕所的设计、气味有关。在一些小城市或者农村地区，旱厕沟渠里暴露的粪便、以及令人窒息的气味就足以让最勇敢的游客哭着回旅馆。

2000多年以来，中国一直在和臭厕所作斗争。在魏朝（公元220-265年），皇室厕所的参观者们也纷纷用纸盒掩鼻以抵挡臭味。

然而，冲厕和厕纸却是由中国人发明，尽管最初只用于皇室。

现在，中国的科学家说他们正在战胜这种臭气。他们推出了一种细菌喷雾，并声称这种喷雾几乎能完全消除厕所的腐臭味。

这种细菌喷雾先是由一组六株细菌分解混合气味，然后再释放一种由橘子皮制成的香水气味。

中国科学院进行的这项“无味厕所”项目宣称要从根本上解决中国的棘手问题。

“2001年到今年年初，五位科学家一直致力于这项课题，”严智英（音译）博士说。这位来自中国科学院成都生物研究所的细菌专家补充说，这项课题已经花费了14万英镑（约149万人民币）。

“一些地方官员在参观污水处理厂时注意到处理技术来自日本，他们希望有本土的解决方法并希望我们为之努力。”严补充。

“我们提取了所有类型的粪便细菌，包括人、猪、鸡、鸭的粪便，并逐个检测了这些化合物”。

“公厕、污水坑或垃圾堆散发的臭味由160多种化合物组成，”他解释道，“这些化合物中的细菌，包括乳酸菌、酵母菌以及放线菌族群，又能互相转化和吸收”。

他说这种中国配方，售价约5英镑（约53元人民币）每升，没有任何副作用，可以用来抵御任何类型生物分解的恶臭。

近些年，北京发起了改善公厕环境的战役。先是引进厕所评级，然后在两年前又出台一项方案：任何设施不得同时有两只以上的苍蝇停留。