February 28, 2010

Cornell Researchers Work to Reduce Energy Usage in Water Treatment

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What happens to Cornell’s dirty water once it goes down the drain? Currently, two percent of the United States’ electricity consumption goes toward treating that wastewater. Prof. Lars Angenent, biological and environmental engineering, and his peers work to reduce electrical consumption by applying bioelectrochemical systems to the wastewater treatment process.

Most wastewater is currently treated using a process called “activated sludge,” in which air is pumped into waste for oxygenation. This aeration process is extremely energy-intensive, and wastewater treatment expends 52 percent of its energy in this step alone.

The waste then moves to thermophilic, anaerobic digester tanks, where microorganisms break down the organic material to produce methane. Unfortunately, only a small part of energy used is gained back in the form of methane. The process, consequently, cannot sustain itself.

Bioelectrochemical systems, like microbial fuel cells, use living microorganisms to generate electric currents and bio-energy from wastewater. A “microbial fuel cell” is a compartmentalized setup of anodic and cathodic electrodes separated by a selectively permeable, cation-specific membrane. Microorganisms living on the electrode removes electrons from the organic waste in the anode compartment. The electrons flow from the anode to the positively-charged cathode compartment, where they are accepted by oxygen.

This naturally-occurring circuit generates energy, but not enough to make this method of wastewater treatment economical. According to Angenent, the biochemical systems possess more value in creating products other than electricity.

“Microbial electrolysis cells” require energy input, but they can produce products, such as hydrogen gas and hydrogen peroxide, which the wastewater treatment process requires. Using the electrolysis cells, the products could be created sustainably at a lower energy cost at the treatment plant Consequently, the plant would never need to get them from non-sustainable sources.

Angenent, director of Cornell’s Wastewater Management Lab, suggested that non-sustainability is a major problem in wastewater treatment. The bioelectrochemical systems may potentially reform this problem, but researchers continue to seek an efficient, scalable system.

Scalability is a problem because many large systems require too much energy input to justify their small yield. However, small systems demonstrate success. For example, “sediment fuel cells” are renewable-energy batteries fueled by settling organic sediment. These fuel cells can power underwater research equipment indefinitely without a new charge or cell replacement. Similar small systems could potentially be used in remote, undeveloped areas to power small devices, like cell phones.

Luckily, researchers can depend on two resources: money and waste.

“It’s very easy to get wastewater. People just want to give it to you, for some reason,” Angenent joked.

Angenent stated that bioelectrochemical technology may still need several breakthroughs to produce a successful cost-efficient alternative to our current waste treatment system.

He stressed the importance of the project, affirming, “We do need to transfer the way we treat wastewater, because now it’s non-sustainable.”

Original Author: Jacquelyn Heim