Anaerobic digesters are mostly used to break down food and animal waste into biogas and other recycable materials.
More and more plants are installing digesters to meet tougher new environmental pollution laws relating to waste disposal. For example potato processors use digestors to decrease greenhouse gas emissions from the plant and save money on fuel costs.
The biogas is produced by anaerobic-aerobic digesters from semi-dry sludge wastes from the process of potato peeling in such processors. The biogas is then used to fuel such machines as steamersand fryers, thus cutting energy costs. Digesters can process all food waste, including meat, bones and dairy products.
In order to help monitor and improve the digesters at such industrial facilities, Miguel Horta and Steve Garrett at Penn State University have designed a sonic gas sensor that can detect the amountof hydrogen or methane that bacteria produce when they break down organic compounds.
The researchers said they hope that acoustics will provide a valuable tool for real-time monitoring of digester performance, improving bio-energy production from organic wastes and conductingstudies of bacteria's metabolic rates.
In the setup, a small loudspeaker creates a sound wave inside a pair of open tubes through which the gas produced by the bacteria is flowing. As the bacteria generate gas, the changing gas concentration alters the acoustic resonance frequency in the tubes.
Microphones connected to specialized electronics track and record this resonance frequency that helps plant monitors precisely determine the change in concentration of the waste gas.
The two researchers are presenting their new technology at the joint meeting of the Acoustical Society of America (ASA) and the annual conference of the Institute of Noise Control Engineering. Thefive-day meeting begins today in Minneapolis, US.