HARVESTING ENERGY FROM 
WASTEWATER TREATMENT

Bruce Logan , Dept. of Civil and
Environmental Engineering  

Funding: The Paul L. Busch Award, from the 
Water Environment Research Foundation (WERF) 

Conventional aerobic wastewater treatment is ordinarily an energy-intensive process.  However, organic matter in wastewater contains energy that has been harvested in various forms, such as methane and hydrogen gases.  We have recently discovered that it is also possible to biologically harvest this energy directly in the form of electricity. Finding ways to generate useful products from wastewater is one the greatest challenges to the Environmental Engineering profession. We will use funds from the Paul L. Busch Award to develop and demonstrate a wastewater treatment plant process for generating electricity while accomplishing wastewater treatment. Biological generation of electricity in a wastewater treatment process represents a completely new approach that will lead to breakthroughs in our approach to wastewater treatment.

The keys to generating electricity using bacteria are to keep the bacteria separated from oxygen during the breakdown of organic matter, and to provide a conductive material for the bacteria to grow on. In order to understand how electricity can be generated by bacteria, it is important to realize that bacteria degrade organic matter by oxidizing it, or through the removal of electrons from a substrate.  To continuously oxidize organic matter bacteria must reduce another compound, typically oxygen or nitrate (i.e. they add electrons to these compounds).  Some bacteria, such as those that reduce iron, can transfer electrons to a carbon electrode. By providing a conductive growth surface for bacteria (anode), linked by a wire to a counter electrode that is exposed to oxygen (cathode), we create current flow and potential.  When the electrons reach the cathode they combine with protons and oxygen to form water.  The ability of bacteria to generate electricity in this manner has been known for some years.  However, it was only recently realized that a system could be developed to simultaneously accomplish wastewater treatment and electricity generation without the addition of any other chemicals.

There are substantial potential economic benefits of a process that generates electricity from wastewater.  For example, complete recovery of electricity from domestic wastewater produced by a community of 100,000 people could conceivably produce 2.3 MW of power.  A more realistic goal is to recover ~0.5 MW of electricity at a rate of around 1000 mW per square meter of surface area for biofilms.  This amount of electricity could power as many as 330 homes. If sold, it would be worth as much as $1.7 million (assumes $0.15/kWh). The recovery of energy from industrial wastewaters such as food processing plants offers additional economic incentive. There are an estimated 20,000 food processing industries, with about half of these producing on average 1 million gallons per day of wastewater, which could be used to produce electricity worth as much as $20 billion annually.

The overarching research goal of this project is demonstrate power generation using domestic wastewater in a reactor that could be built at the pilot scale.  For this objective, we will demonstrate this electricity-generating technology using domestic wastewater from the Penn State Wastewater Treatment plant. Through this research, we will achieve methods to provide more cost effective reactors that can lead to successful scale up for the wastewater treatment system of the future that will accomplish both wastewater treatment and electricity generation.