In the Lab

• By Heida Diefenderfer
• May 01, 2003

It Pays to Convert Food Processing Wastewater to Energy Source
In laboratory tests, Penn State environmental engineers have shown that wastewater from a Pennsylvania confectioner, apple processor and potato chip maker can produce hydrogen gas worth $80,000 a year or more. Steven Van Ginkel, doctoral candidate, and Dr. Sang-Eun Oh, postdoctoral researcher in environmental engineering, conducted the tests.

"In addition to hydrogen, which can be used as a fuel and industrial feedstock, methane, the main component of natural gas, can be generated from the wastewaters," he notes. "Over 10 billion BTUs of energy from methane could be produced every year at a single one of these food processing plants."

Van Ginkel adds, "By extracting hydrogen and methane from their wastewaters, these plants can also reap significant savings by not needing to aerate. Aeration makes up 20 to 80 percent of wastewater treatment costs."

The researchers presented the Penn State team's findings in a poster, "Turning Pennsylvania's Waste Into Energy," at Penn State's Hydrogen Day, a special event for industry and government representatives. Co-authors are Dr. Oh and Dr. Bruce Logan, director of the Penn State Hydrogen Energy Center and the Kappe professor of environmental engineering.

In the tests, Van Ginkel and Oh added hydrogen-producing bacteria to samples of wastewater from the Pennsylvania food processors. The bacteria were obtained from ordinary soil collected at Penn State and then heat-treated to kill all bacteria except those that produce spores. Spores are a dormant, heat-resistant bacterial form adapted to survive in unfavorable environments, but able to begin growing again in favorable conditions.

"The spores contain bacteria that can produce hydrogen and once they are introduced into the wastewater, they eat the food in the water and produce hydrogen in a normal fermentation process, "Van Ginkel says. Keeping the wastewater slightly acidic helps to prevent any methane-producing bacteria from growing and consuming hydrogen.

After only a day of fermentation in oxygen-free, or anaerobic conditions, the hydrogen-producing bacteria fill the headspace in the fermentation flasks with biogas containing 60 percent hydrogen and 40 percent carbon dioxide.

In the second stage of the process, the acidity in the wastewater is changed and methane-producing bacteria added. The bacteria eat the leftovers, grow and generate methane.

The solid material or sludge left over from fermentation is only one- fourth to one-fifth the volume from typical aerobic treatment processes.

Van Ginkel says, "Using this continuous fermentation process, we can strip nearly all of the energy out of the wastewater in forms that people can use now. While this approach has high capital costs at the outset, our calculations show that it could pay off well both environmentally and financially for some food processors in the long run."

For more information, please visit www.psu.edu.

Scientists Study Water Movement in Different Types of Soil to Trace Groundwater Contamination.
A phenomenon occurring in soil that has been baffling scientists for the past 20 years finally has some answers, thanks to a water movement model created by researchers at the University of California-Riverside. The research is published in the February 2003 issue of Vadose Zone Journal, published by the Soil Science Society of America.

These researchers used observations of water movement from laboratory and field experiments over the last three years to create a model to predict the redistribution of water in the soil following irrigation or rainfall. They specifically studied what causes the water to break up into narrow channels, called fingers, that can move much deeper into the soil, even when there are no apparent cracks or holes in the soil.

The model assumes all soils are unstable during this redistribution of water, but only coarse-textured soils will form fingers capable of moving significant distances. For example, laboratory experiments in coarse sandy soil showed that as little as two inches (five centimeters) of water added to dry soil would create fingers that could move more than 3.2 feet (one meter). In addition, the wetted pathways formed by the fingers remained in soil for long periods of time and were able to channel subsequent water applications as long as a month later.

"These findings help explain field observations of deep chemical movement in soils without cracks or holes that have baffled other scientists and myself for over 20 years," said William Jury, professor, University of California-Riverside, and principal investigator on the project, which was sponsored by the U.S.-Israel Bi-national Agricultural Research and Development Fund (BARD).

The research discovery has serious implications for agricultural water management in coarse-textured soils. Fingering can move water and agricultural chemicals below the crop root zone, which is costly and inefficient and can increase the possibility of ground water contamination. The researchers suggest that longer and less frequent watering might decrease the possibility of fingering near the surface.

For more information, please visit www.asa-cssa-sssa.org.

This article originally appeared in the May 2003 issue of Environmental Protection, Vol. 14, No. 4.

This article originally appeared in the 05/01/2003 issue of Environmental Protection.