Rotten potatoes and unwanted chicken wings represent a novel form of energy, otherwise they could risk food safety, said two Chinese political advisors who called for legislation against improper handling of kitchen waste.

"The legislature should make laws to guarantee that kitchen waste is properly treated and recycled into assets," said Yao Aixing, a member of the National Committee of the Chinese People's Political Consultative Conference (CPPCC), the top political advisory body.

Yao's proposal came at a time when most Chinese people, who have more disposable income, seem to be less thrifty when consuming food.

Food safety concerns

Yao serves as vice governor in charge of food safety affairs of the Ningxia Hui Autonomous Region. He warned that the growing amount of catering leftovers would put food safety and the natural environment under threat.

Each year, kitchen waste was "processed" into two to three million tonnes of swill-cooked dirty oil, which sneaked back to dining tables through an underground muck-money network, Yao cited official media reports as saying.

"This poses a serious danger to the food safety of citizens," he said.

The kitchen leftovers, thought to be a good source of digestible energy and high-quality proteins, might end up as feed for livestock such as pigs and chickens, as a supplement to their diet, the advisor said.

However, food safety experts said kitchen leftovers were a source of infection for animals, which, in extreme cases, could result in contamination of meat or eggs and cause illness among people who consume livestock products.

Growing kitchen waste also takes a toll on the environment, which falls victim to the leftovers that are kept away from people's dining tables and livestock feed, said Yao.

Burnt kitchen waste together with other household garbage in rubbish incineration power plants would greatly increase the emission of dioxins, a toxic gas, Yao said in his proposal.

Huge energy drain

Shi Yaozhong, another member of the CPPCC National Committee, submitted a similar proposal in which he also raised questions about energy waste as a result of the improper treatment of kitchen waste.

Chinese cities churn out at least 60 million tonnes of kitchen waste each year, representing the calory equivalent of grain harvested from 12 million mu (800,000 hectares) of farmland, said Shi, citing data from the School of Environment in Tsinghua University.

In 2009, at least one hundred billion yuan (15.2 billion U.S. dollars) was wasted in the form of leftovers from China's catering sector, he said.

Government data from some developed countries showed that an estimated 27 percent of the food available for consumption ended up as kitchen waste in restaurants, cafeterias and individual homes, said Shi.

With no official data released in China, Shi estimated that leftovers could account for 20 percent to 30 percent of the food on dining tables in China.

After receiving high-temperature treatment, kitchen waste can be processed into safe feed for livestock while the swill fat refined from the waste can be used to supplement raw material for producing soaps and paint and the leftovers can serve as fertilizer, Yao said in his proposal.

Legislation is key

In developed countries, there are laws regulating kitchen waste treatment, and an environment-friendly industry has came into being as a result, said Yao, pointing to the absence of such a law in China.

Shi and Yao called for the national legislature to roll out regulations to demand restaurants hand in their leftovers once a day to collectors from professional kitchen waste treatment companies.

After the case of swill-cooked dirty oil was revealed, four ministries, including the top economic planning body, the Ministry of Housing and Urban-Rural Development and the Ministry of Environmental Protection jointly launched a trial program last May for proper treatment of kitchen waste.

The ministries' move was followed by the State Council, China's Cabinet, which issued a decree for enhancing the regulation of swill-cooked oil and kitchen waste in July 2010.

Nearly 20 Chinese cities, including Beijing and Shanghai, have rules concerning kitchen waste treatment but enforcement has been weak due to the absence of a national law, said Shi.