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Biochar Shows Potential For Reducing Wastewater Contaminants
November 19, 2020

Sewage treatment plants across the country are facing an increasingly difficult challenge in the treatment of wastewater — efficiently and effectively removing toxic pharmaceutical compounds.

Now, according to information provided by The Pennsylvania State University (Penn State), researchers have discovered that biochar, a charcoal-like substance created primarily from agricultural waste products, holds promise for removing emerging contaminants such as pharmaceuticals from treated wastewater.

With support provided by the U.S. Department of Agriculture’s National Institute of Food and Agriculture and USDA’s Agricultural Research Service, a team of Penn researchers have conducted a novel study that evaluated and compared the ability of biochar derived from two common agricultural waste products, cotton gin waste and guayule bagasse, to adsorb three common pharmaceutical compounds from an aqueous solution.

Guayule, a shrub that grows in the arid Southwest, provided the waste for one of the biochars tested in the research. More properly called Parthenium argentatum, it has been cultivated as a source of rubber and latex. The plant is chopped to the ground and its branches mashed up to extract the latex. The dry, pulpy, fibrous residue that remains after stalks are crushed to extract the latex is called bagasse.

According to researcher Herschel Elliott, a Penn State professor of agricultural and biological engineering, the results are important because they demonstrate the potential for biochar made from abundant agricultural wastes to serve as a low-cost additional treatment for reducing contaminants in treated wastewater used for irrigation.

“Most sewage treatment plants are currently not equipped to remove emerging contaminants such as pharmaceuticals, and if those toxic compounds can be removed by biochars, then wastewater can be recycled in irrigation systems,” Prof. Elliott noted. “That beneficial reuse is critical in regions such as the U.S. Southwest, where a lack of water hinders crop production.”

The researchers used three pharmaceutical compounds in the study: sulfapyridine, an antibacterial medication no longer prescribed for treatment of infections in humans but commonly used in veterinary medicine; docusate, widely used in medicines as a laxative and stool softener; and erythromycin, an antibiotic used to treat infections and acne. Each was tested to determine whether the biochars would adsorb them from an aqueous solution.

Published in the journal Biochar the findings of the study, Adsorption of pharmaceuticals from aqueous solutions using biochar derived from cotton gin waste and guayule bagasse, suggest biochars created from agricultural waste materials could act as effective adsorbents to remove pharmaceuticals from reclaimed water prior to irrigation.

However, results from the study demonstrated that the biochar derived from cotton gin waste was much more efficient, adsorbing 98% of the docusate, 74% of the erythromycin and 70% of the sulfapyridine in aqueous solution. By comparison, the biochar derived from guayule bagasse adsorbed 50% of the docusate, 50% of the erythromycin and just 5% of the sulfapyridine.

The research also revealed that a temperature increase, from about 650 to about 1,300 degrees F in the oxygen-free pyrolysis process used to convert the agricultural waste materials to biochars, resulted in a greatly enhanced capacity to adsorb the pharmaceutical compounds.

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