Washington, July 12: Scientists at the US Department of Agriculture (USDA) say that manure can be used as a filter to leach heavy metals from wastewater, if turned into porous activated carbon.
The research chemist at the Centre Isabel Lima has devised a way to turn chicken manure into such carbon, USDA said.
Food animals in the us produce 350 billion tons of manure each year.
“Animals,” said Lima from her office at USDA’s southern regional research centre in New Orleans, “leave behind incredible amounts of manure. We wanted to see if there was a way to transform it and add value.”
Lima’s team first charred the manure, heating it in an oxygen-free environment to boil off volatiles and pollutants, leaving a carbon-rich, charcoallike residue. Then they bombarded the residue with steam, imparting porosity to give it a large amount of surface with which to catch impurities.
Lima said that most activated carbons are made from coal, wood or plant residuals such as groundnut shells, soyabean hulls or coconut husks, and are best used in removing odour and organic materials from drinking water.
Unlike these products, chicken manure turns out to have an unusual ability to extract from industrial wastewater positively charged metal particles such as zinc, copper and cadmium, many of which are carcinogens (cancer-causing).
Lima’s team is conducting further tests to find out how this happens. The team is also trying to reduce the cost of making manure carbon. In the targeted industrial market, where coal is currently the predominant raw material, manure has an advantage. “Coal is expensive and nonrenewable,” Lima said. “With manure, the raw material is free.”