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25 June 2009

Mud goes green as a fuel

Using mud from wastewater treatment plants as a partial alternative fuel can enable cement factories to reduce their CO₂ emissions and comply with the Kyoto Protocol. On top of that, using the mud will pose no risk to human health and will end up being profitable.

Dependency on oil and coal could be coming to an end. Researchers from the Rovira i Virgili University (URV) in Spain have analyzed the environmental and human health impacts of an alternative fuel that solves different problems simultaneously. One problem is removing solid waste from water treatment plants of large cities.

A cement factory is now getting 20% of its fuel from wastewater treatment plant mud.

Scientists conducted a study into this method at a cement plant in Vallcarca (Catalonia), which has been producing cement for more than 100 years, and they said it is “the best option for getting rid of mud that would have had to be dumped elsewhere, while also powering the plant.”

“As this mud is already waste, burning it does not enter into the atmospheric CO₂ emissions assigned to each country under the Kyoto Protocol,” said José Luis Domingo, lead author of a study on the subject and director of the Toxicology and Environmental Health Laboratory at the URV.

This would enable plants producing cement, one of the most contaminating industries in terms of CO₂ as well as emissions of dioxins, furans, and heavy metals, to consume energy in a more environmentally-friendly way. Wastewater treatment plant mud replaced up to 20% of the fossil fuel energy used at the Catalan plant.

From an economic point of view, the scientists will not say cement plants could increase their profits by using this method, but “they will not have to pay anything to exceed their agreed emissions,” Domingo said. The economic benefits of this system also depend on the price of fuel.

One of the most important issues for the URV scientists is the reduction in environmental impact, and consequently the health risks for people living near the plants. The experiment with the mud has led to a 140,000 metric ton reduction in CO₂ emissions between 2003 and 2006, and will have limited the potential deaths from exposure to chemical pollutants. In addition, the study shows using this green fuel would reduce the cancer rate by 4.56 per million inhabitants.

The researchers said it is essential to carry out separate studies for each plant because “we still don’t know whether this will be positive for the whole cement industry,” Domingo said. However, if the conditions are right, using mud from wastewater treatment plants in cement factories is “a very good solution,” he said.

For related information, go to www.isa.org/manufacturing_automation.