Electrical Power from Wastewater Sludge


The U.S. generates 8 million dry metric tons of sludge each year. The costs of disposing this sludge are roughly $2 billion dollars annually and the EPA spends about 1/5th of their budget ($1.4 billion dollars) on wastewater management. For individual wastewater treatment plants (WWTP), ‘dewatering’ the sludge is one of the primary operating costs. This, combined with a renewed focus on conversion of biosolids to fuel, has led to new and innovative approaches to wastewater processing. Drs. Chuck Coronella and Victor Vasquez at the University of Nevada-Reno have come up with an alternative wastewater processing system named Sludge to Power (S2P) that produces electricity onsite from dried wastewater biosolids, while eliminating a waste stream of millions of tons per year per plant. The EPA estimate that 60,000 dry metric tons of sludge are produced annually in Nevada alone, which could turn this into 11 megawatts of power.

Benefits & Advantages

  • Enables renewable energy production
  • Less energy consumed compared with traditional drying systems
  • Greatly reduced footprint for overall wastewater drying process
  • Significant cost reduction

Technology Overview

Existing dewatering techniques include the use of decanter centrifuges or plate and frame filter presses, as well as polymer coagulants, to decrease the moisture content of the sludge, from 96-98%, to 70-85% prior to disposal. The high moisture content of the sludge, even after dewatering, results in extremely high disposal costs with the combined cost of treatment and disposal of solids being up to 50% of the total WWTP costs. The S2P technology uses the WWTP biosolids as a renewable fuel source for power production as an alternative to landfill or other disposal methods. Dry biosolids from WWTPs have an energy content of approximately 20 MJ/kg, about the same as soft coals mined in the United State. The biosolids contain compounds that can be mostly volatilized through gasification with the syngas being used for power production in a commonly available combustion turbine or internal combustion engine. Gasification significantly reduces the amount of solids that require disposal with only 6.5% of the biosolids leaving the gasification unit as ash and charcoal.

Through traditional means, including coagulants, flocculants, filter press, centrifugation, etc., moisture in wastewater sludge can be brought down to about 70-85%. Incineration and landfilling are two common techniques for disposing of sludge, but the costs of both are greatly exasperated by the presence of more than 50% water. Drying to lower moisture levels requires expensive drying techniques. Dried sludge is a fuel, similar to soft coals with a heating value of 8600 Btu/lb. It can be converted to renewable power by gasification and combustion. Each ton per day of 80% moisture can be converted to about 10 kWe. In other words, a plant that generates 100 tons per day of wet sludge can convert an expensive disposal problem into 1 MWe of renewable power, leaving only 6 tons per day of dry inert ash to for disposal. Sludge2Power is the name of our new cost-effective, renewable, energy-efficient, process for reducing moisture from 70-85% down to 5-10%.

Intellectual Property

UNR ID#: UNR08-023
Title: System and Method for Energy Production from Sludge
U.S. Publication #: US-2010-0043445-A1


Patent Information:
For Information, Contact:
Dan Langford
Technology Commercialization, Manager
University of Nevada, Reno and Desert Research Institute
Charles Coronella
Victor Vasquez
Renewable Energy