Clockwise from top: A police officer in Nantong, Jiangsu province, shows local residents how to distinguish gutter oil from the genuine article. The classes are part of a September campaign in the city to reduce the use of recycled gutter oil in public eateries. A worker processes gutter oil into biodiesel at the factory of Jiangsu Clean Environmental Technology Co Ltd in Suzhou. The company is one of only a handful in China that are allowed to recycle the waste into fuel. Zhao Feng collecting swill from a restaurant in Suzhou. Zhao and his father Zhao Jinghua can earn a combined 10,000 yuan a month by collecting gutter oil and waste from 100 restaurants in the city every day. All the waste oil they collect is transported to Jiangsu Clean to be processed into biodiesel. Xie Yu / China Daily