July 2010, Vol. 22, No.7

Research Notes

Grass Shows Promise for Antibiotics Remediation

Michigan Technological University (Houghton) undergraduate students have been assisting in research that has uncovered some interesting applications for vetiver grass. The grass, a native of India often grown in artificial wetlands to clean water, is a noninvasive plant that quickly produces large amounts of biomass, according to a university news release.

Rupali Datta, associate professor in the university’s Department of Biological Sciences, has used vetiver grass extensively in her lab. She has researched its ability to remove such metals as lead and arsenic, as well as such organics as trinitrotoluene (TNT), from the environment, she said. Datta hypothesized that the grass could work for antibiotic remediation and suggested the idea as a project for university student Stephanie Smith.

Smith worked with Datta to design an experiment using sterile vetiver grass to address the issue of antibiotics in water, the news release says.

Smith grew vetiver hydroponically — in a nutrient solution — exposing it to various concentrations of tetracycline and monesin, two antibiotics used to treat dairy cattle, the news release says. When these antibiotics are given to cows, 70% is excreted in an active form, Smith said.

While antibiotics concentrations in drinking water are unlikely to affect those consuming the water, scientists are concerned that releasing antibiotics indiscriminately into the environment may encourage antibiotic-resistant strains of bacteria and make it harder to treat diseases, the news release says. There also are concerns with using solids that contain antibiotics to fertilize crops and water that contains antibiotics to irrigate crops, Smith says in the news release.

At the end of the 12-week study, all of the tetracycline and 95.5% of the monesin had disappeared from the solution. The preliminary results show that vetiver had taken up and metabolized both drugs into the plant’s tissue. In addition, the plants in the tetracycline solution grew much faster than the control plants, and the plants in the monesin grew somewhat faster than the control plants, Smith explained.

The study’s results indicate that vetiver also could be used to remediate nutrients in wastewater, the news release says. “Vetiver has been shown to absorb high amounts of phosphorus in wastewater,” Datta said. “It also absorbs moderate amounts of nitrogen, which makes it a perfect candidate for wastewater treatment.” Australia has used vetiver to treat wastewater; and Aceh, Indonesia, now has vetiver systems installed as subsurface flow wetlands or vegetated leach fields, she added.

Datta will continue working on the project with the help of other students at the university — Smith was scheduled to graduate in May. In a collaborative effort between Michigan Tech and Montclair (N.J.) State University, research is currently in progress analyzing vetiver to determine what happens to the antibiotics in plant tissue, Datta said.

“Other aspects being studied are the potential for phosphorus reduction in wastewater,” Datta said. In addition, researchers at Montclair State are working on researching the mechanism of TNT remediation.


New System Transforms Solids Into Energy

A system generating electricity from wastewater biosolids is scheduled to be set up in the Truckee Meadows Water Reclamation Facility (Reno, Nev.) this summer. The demonstration-scale system is designed to process wastewater solids at a rate of 9 kg/h (20 lb/h). The system, which dries the solids into a solid fuel, is the product of a renewable energy research project at the University of Nevada (Reno), according to a university news release.

The university will study its patent-pending technology to see if the fuel generated is suitable for gasification and, ultimately, conversion to electricity. The researchers will investigate how dry the fuel becomes, what the material’s fuel value is, and what the metal content is, said Chuck Coronella, principal investigator for the research project and associate professor of chemical engineering at the university.

“Our innovation is a low-temperature fluidized bed, with inert solids serving as a very fast heat-transfer medium,” Coronella said. The continuous-feed demonstration system is the size of a refrigerator and will help researchers determine the optimum conditions for a commercial-size operation, the news release says.

For the current trial, wet solids are fed to a fluidized-bed dryer operating at 77°C (170°F), Coronella said. The fluidized bed is composed of inert solids, such as sand, that are agitated rapidly. The moving inert material breaks the wet solids into smaller pieces that dry quickly. The dried solids leave the bed as a fine powder entrained in the air. “The current trial will validate only the low-temperature dryer, not the generation of power,” Coronella explained.

The trial also will test drying solids continuously, which poses a challenge, even though the feed rate is extremely small compared to the needs of typical wastewater treatment facilities, Coronella said. After completing the small-scale test, the researchers plan to conduct a large-scale test capable of handling feed rates common to a small- or medium-size facility. “The next demonstration will be integrated and will include dewatering, drying, gasification, and power production,” Coronella said.

Truckee Meadows agreed to the trial after being approached by Coronella and setting up an interlocal agreement between the cities of Reno and Sparks, co-owners of the facility, explained Starlin Jones, operations and maintenance manager of the facility. To install the system at the facility, the researchers need to install a gasifier and some kind of combustion facility to convert the dried fuel to power, Coronella explained.

“The system that we are developing needs no additional fuel for drying,” Coronella said. “Most of the heat required for drying is provided from waste heat derived from combustion of the dried fuel.”

The major benefit of the new technology is that it enables complete solids management onsite. That change would reduce trucking costs and biosolids disposal fees while also potentially generating 14,000 kw•h per day to offset plant power needs, the news release says.

“The challenge has been developing a cost-effective means to convert de-watered sludge to a dry fuel,” Coronella said. Coronella estimates that plants generating more than 91 Mg/d (100 ton/d) will be able to justify the costs of installing this type of system.

University researchers began working on converting sludge to electric power in 2005 after being solicited by the California Energy Commission to study the topic and receiving the Energy Innovations Small Grant to fund the research, Coronella said. The newest phase of the project received funding from the Tech Transfer Office under a U.S. Department of Energy grant.


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