Scientists gather energy from ‘wet waste’

Scientists at the University of California are developing a way of converting ‘wet waste,’ such as sewage sludge and grass clippings, into synthetic diesel fuel and electricity.

Scientists at the University of California, Riverside are developing a way of converting ‘wet waste,’ such as sewage sludge and grass clippings, into synthetic diesel fuel and electricity in a move that could potentially reduce the need for landfill space.

Colin Hackett, manager of the Alternative Fuels and Renewable Energy Program at UCR, is overseeing the research, funded by Riverside Public Utilities and Eastern Municipal Water District. The program is housed in the Bourns College of Engineering – Centre for Environmental Research and Technology (CE-CERT).

Wet waste has historically been difficult to use as a fuel source because previous technologies required the waste be dried before conversion into fuel.

By adapting the hydro-gasification conversion process, originally developed to produce clean-burning gases from coal, CE-CERT expects to be able to convert water and carbonaceous waste feeds into clean burning fuels and electricity.

CE-CERT’s multi-stage fuel production process uses high temperature and pressure to produce gases that can be used for fuel synthesis or electrical power generation.

‘The system requires no additional fuel or energy other than the chemical energy in the waste feed,’ Hackett said. ‘This process has enormous potential for energy conversion from any wet-waste that contains carbon.’

The potential return is two-fold when fuelled by biosolid waste, which is the by-product of municipal wastewater (sewage) treatment. Currently, that waste is spread on farm fields, placed in landfills, or mixed with green waste to produce a soil amendment. The biosolids would quickly and simply be converted into useful forms of energy by the CE-CERT process.

What is left over from the process is expected to be a fine, inert debris or ash that could be mixed into such products as asphalt or other construction materials, Hackett said.

The five wastewater plants at Eastern Municipal Water District produce about 130 tons per day of biosolid waste. If just that waste were run through the new CE-CERT process, it could produce each day up to 26 barrels (1092 gallons) of synthetic diesel fuel and up to 34 megawatt-hours of electricity, which is said to be enough power for about 3,000 homes.

Similar energy production could be expected from wood, paper and green waste collected by the city-operated Riverside Public Utilities.

Hackett said he hopes to have a scale model of the new process up and running this month. If the testing phase is successful, a full-scale demonstration unit could be produced and operating by 2004.