People accused of being involved in a gutter oil selling case stand trial on Tuesday in Ningbo, Zhejiang province. Provided by Ningbo Intermediate People's Court

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.