NSF-SGR

Determination of the Potential for Direct Generation of Electricity from Wastewater Using a Microbial Fuel Cell

PIs:
Bruce Logan , Dept. of Civil and Environmental Engineering;
Tom Mallouk, Dept. of Agronomy and Soil Science

Funding: National Science Foundation
(June 2002 - May 2003) BES-0331824

Project Summary

The basic processes developed for wastewater treatment (activated sludge, trickling filters and lagoons) were developed over a century ago, and have changed little with respect to the fundamental approach of oxidizing organic matter solely to remove the organic load on receiving water bodies. Although the water quality of our streams and rivers has improved, wastewater treatment remains an economic burden to industries and the public. Organic matter in a wastewater has energy value, particularly industrial wastewaters that have high concentrations of organic matter. A substantially different approach will be taken to wastewater treatment that is based on electricity production directly from organic matter in wastewater. This approach is based on the anaerobic oxidation of organic matter in a mediator-less microbial fuel cell (MFC).

While current generation using bacteria has been known to be possible for over a decade, only recently has it been shown that chemical mediators (toxic chemicals added to a reactor) are not needed. This finding that chemicals do not need to be added to wastewater could drive development of a completely new wastewater treatment technology based on MFCs. What is needed is a method to increase power flow by optimizing a fuel cell for use with bacteria (as opposed to hydrogen and inorganic catalysts). In a MFC, the potential created between electron carriers in the bacterial respiratory chain and oxygen is harvested by allowing bacteria to transfer electrons from respiratory enzymes to an electrode (anode) while still in an anaerobic environment. A second electrode (cathode) is kept in an aerobic environment, so that a potential is created. The flow of electrons from respiratory enzymes located on the outer membrane of the bacteria across this potential creates current which can be captured.

The purpose of this SGER proposal is to demonstrate the feasibility of this MFC approach for wastewater treatment, and to show for bacteria we must optimize current flow at the cathode. In this project we will demonstrate power generation from wastewater is optimal for current flow in an MFC when substrate is first fermented, and that power generation can be much higher than previously believed. We will construct three types of MFCs in the laboratory: a batch system with a salt bridge that mimics a seawater type of fuel cell; an otherwise identical system that uses a proton exchange membrane (PEM); a fully optimized cathode that uses a direct air system.

This research provides a completely new avenue for wastewater treatment based on using bacteria to harvest energy from organic matter. The results could be of enormous global environmental benefit by ensuring the treatment of wastewater (to generate electricity) and also economic benefit by reducing costs for existing wastewater treatment systems.