Description:
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
