Eleven suspects involved in refining and selling gutter oil stood trial in Ningbo, East China's Zhejiang province, on Tuesday.

The 11 suspects are alleged to be part of a large group that is recycling used kitchen oil, often retrieved from gutters and sewers, and reselling it as edible oil.

The court didn't pronounce a verdict in the case.

Ningbo Intermediate People's Court tried nine people from the same group last week, including the alleged group leader, Liu Liguo. Altogether, 20 people have been charged for their alleged participation in the network, which police say runs from Zhejiang to Shandong and Henan provinces.

Police in Ningbo first discovered the network in March 2011, after they detained a man surnamed Huang who salvaged gutter oil in the city. Arrested later was Liu Liguo, head of two companies in Shandong province, who police said had been buying gutter oil from Huang.

Police then discovered a number of food and cooking-oil distributors who bought recycled oil from Liu and resold it.

Police in Zhejiang and Shandong raided Liu's production sites in Shandong in July 2011, and confiscated about 670 metric tons of gutter oil.

Prosecutors said that Liu's companies had sold 99.2 million yuan ($15.6 million) worth of gutter oil since December 2007.

The 11 people who stood trial on Tuesday morning are from Huikang Oil Co in Henan province.

Prosecutors said the company had been buying gutter oil from Liu, blending it with edible oil and earning more than 150 million yuan by selling it to companies in Henan, Hebei, Hubei and Shanxi, including food makers, fodder makers and a pharmaceutical company.

Bu Qingfeng, head of Huikang company, said in court that the oil his company sells is vegetable and edible oil, but he is not aware of how the company contacted Liu or decided to buy gutter oil from him.

In February, the Supreme People's Court, together with the Supreme People's Procuratorate and the Ministry of Public Security, issued a statement on the crackdown of the production and selling of gutter oil. People making or selling gutter oil as food oil can be sentenced to life imprisonment or even death if their products kill or severely injure consumers.

Prosecutors also exhibited the assessment on Liu's gutter oil by Beijing Food Supervision Center to further prove that it was poisonous. The assessment shows the sample contains polyaromatic hydrocarbons, excessive acid and cholesterol.

Yan Weixing, a researcher at the China National Center for Food Safety Risk Assessment, said that kitchen waste such as cooked oil may contain excessive acid value and cholesterol and even carcinogens.

Excessive acid value means that the oil has gone bad, he said, and if the oil contains cholesterol, it shows that the oil has animal fat, which is common in leftovers.

"The production and selling of gutter oil as food oil should be stopped at its source," Yan said.

"Some manufacturers blend gutter oil with edible oil and make it undetectable. They can even make gutter oil that almost feels the same as normal edible oil. As a result, to catch those responsible red-handed is very important."

Contact the writer at wangqingyun@chinadaily.com.cn.