TechnologyMSolutions Beautifying wastewater treatment
ADNANE HITMI
wastewater, by 91%, and cut chemical oxygen demand, the amount of oxyA new wastewater treatment involvare worth $413/gram and in high degen that would be required to chemiing constructed wetlands and mand by the pesticide industry, accally degrade the organic compounds chrysanthemums may provide a colcording to his research. in wastewater, by 99%. orful solution to small European Phillippe Vernay, a chemist inThe levels of heavy metals and Union (EU) communities scrambling volved in the project, says that the organic contaminants in the treated to cope with wastewater treatment treatment wetland’s aerobic nature is wastewater were very low, Hitmi says, rules set to go into effect in 2005. responsible for the surprisingly high noting that it is unlikely the effluent Researchers are constructing a pilotuptake of ammonia, which was virtufrom a small, rural community would scale plant in France to test the deally eliminated by 72 hours of treatcontain high levels of such pollutants. sign, which laboratory studies show is ment during the tests. The ammonia Nonetheless, he plans to investigate particularly effective at removing amwas converted to nitrite and subsethe issue further. monia from wastewater. quently oxidized to nitrate, which is When the researchers used the Most wetland treatment chlorophyll A fluorescence systems rely on anaerobic measurements that have organisms to take up nubeen established as a means trients like nitrogen and of detecting physiological phosphorus from wastechanges in response to enwater. The new French vironmental stress, they method, which is defound that the chrysanthescribed in the May 1 issue mums grown on sewage of ES&T (Environ. Sci. wastewater performed simTechnol. 2002, 36, ilarly to a control group 2101−2106), follows a difgrown hydroponically. ferent approach by creatThe main inspiration ing conditions that allow behind devising a wetlandaerobic organisms to take based technique for water up the nutrients. treatment was to help small The oxygen-dependent towns in the Auvergne remicrobes that thrive on gion, a hilly, agricultural area the roots of the wetland’s in the middle of France, chrysanthemum plants comply with the upcoming The foxglove plantsin thislaboratory-scale w etland forcleaning are responsible for most EU directive, which will outw astew aterhave the potentialto offsetthe costsofoperation. of the water treatment, law dumping the copious explains Adnane Hitmi, a quantities of sludge proplant physiologist at Auvergne taken up by the plants, according to duced via traditional wastewater treatUniversity’s Biotechnology and the paper. Anaerobic treatment wetment in landfills, Hitmi says. Environment Laboratory and the lands have a lower efficiency because Because of the amount of land it paper’s corresponding author. In fact, they have a limited electron transfer will take up, the technology is aphe says the nitrogen and phosphocapability, Vernay explains. propriate for communities of fewer rous in the wastewater effluent are Overall, the laboratory-scale wetthan 1000 people, says Hitmi, noting the plants’ main nutrients. land took up 40−80% of the nitrogen that communities of this size are beBefore settling on chrysantheand phosphorus from the wastewater coming more common throughout mums, Hitmi and his colleagues exthat it was used to treat, which initialEurope. perimented with a wide variety of ly contained 13.3−100.6 milligrams/ The test system builds on the replantsincluding roses, digitalis liter (mg/L) of total nitrogen and search of William Jewell of Cornell (foxglove), geraniums, and even to3.8−15.7mg/L of total phosphorus. University’s Agricultural and Biological baccoover the course of five years. The chrysanthemums also removed Engineering Department, who has A project goal was to offset the wet95% of the wastewater’s suspended been investigating how wetlands can land’s cost by growing a product with solids. It reduced biological oxygen be used as a secondary treatment for a resale value, Hitmi says. Chrysandemand, a measure of how much oxysewage wastewater that has underthemums are the principal source of gen microorganisms would use to degone anaerobic treatment. It is expyrethrins, natural insecticides that compose the organic matter in tremely simple, consisting only of a © 2002 American Chemical Society
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single tank, an electric pump, and 25 chrysanthemum plants. In time, the researchers hope to eliminate the pump. The test treatment involved continuously circulating 30 L of untreated wastewater for 72 hours, so it came into contact with the roots of chrysanthemums, which were grown using soil-less nutrient film techniques widely used in the greenhouse industry for hydroponic growing. A major advantage of this hydroponic system is that, unlike wetlands that require soil or some substrate material to house the bacteria responsible for the bulk of the chemical transformations, it produces very little waste that must be disposed of as sludge, Hitmi says. It currently appears as if the plant roots will be considered sludge, but the researchers say an upcoming EU directive may define compost in such a way that the roots could be considered compost. The chrysanthemums themselves should be salable, the researchers agree. Vernay’s analysis shows that pyrethrins harvested from the chrysanthemums exposed to wastewater were not significantly different than a control group grown on a standard nutrient solution. He says that he has sent a batch of wastewater-derived pyrethrins to a pesticide factory that is producing pyrethrins to see if they are acceptable. It may also be possible to sell the plants locally as ornamentals, he says. The researchers will have a great deal more data once the pilot plant they are constructing in the nearby city of Senilhes, which has 100 inhabitants in the winter and 350 in the summer, is operational early next year. The pilot test will help the researchers answer some important questions, Hitmi says, such as what will happen if the plants freeze in the winter. Because the system could be destroyed if herbicides are present in the wastewater, the researchers will see if they can educate Senilhes’s inhabitants to dispose of such materials through another route. Whether or not the treatment system will ultimately be cost-effective depends upon the cost of land and the cost of sludge disposal in the area, Hitmi says. But he is hopeful about the treatment’s prospects becauseif all goes as hoped—it won’t require energy or any water other than wastewater and should be very inexpensive to operate. —KELLYN S. BETTS 252 A
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