Researcher to turn sewage sludge into combustible gas

A US professor has developed a process allowing difficult to dispose of sewage sludge to be turned into a combustible gas with a positive by-product, methane gas.


Currently sewage sludge, the harmful of the two by-products of treating raw sewage, is incinerated using a substantial amount of fuel, as it is composed of about 95% water, as well as producing harmful gases, such as sulphur and nitrogen oxides.

Using a waste gasification process called ChemChar, Stanley Manahan, a chemistry professor at the University of Missouri-Columbia, believes that the sewage sludge can be converted into a combustible gas comprised of carbon dioxide, elemental hydrogen, carbon monoxide and small quantities of methane. The process has already been shown to almost completely eliminate polychlorinated biphenyls (PCBs), Chlorofluorocarbons, Organophosphates used as surrogates for military poisons, or ‘nerve gases’ and organohalides.

But, while disposing of these chemicals is an expensive process, Manahan’s research has shown that the only materials required are the sludge itself and oxygen as energy for the process is provided by the gases generated. ChemChar is a thermal process in which fuel on a porous carbon matrix (Char) reacts with a substoichiometric amount of oxygen to destroy organic molecules and to produce a combustible gas containing no dioxins, like conventional incineration.

Furthermore, combustion of the gas product, which may be carried out over a catalyst, ensures total destruction of any waste products or by-products that may have escaped gasification. In the case of sewage sludge, char made by gasifying the sludge can be used to treat and dry the sludge, with the resulting mixture of char and sludge then being gasified to make additional sludge for treatment of yet more sludge.

“The process ultimately eliminates sewage sludge and results in a mineral material,” Manahan told edie. “Eventually, we get an carbon ash product that can be used as lime on fields. It’s an innocuous product that can be readily disposed of or utilised”.

“I see the potential of using the ChemChar process for treating sewage sludge as being really quite important but unfortunately we need about $3 million to make it become a reality”, Manahan added.

For further information please contact manahans@missouri.edu

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