Much of the antimicrobials (AM) used therapeutically and prophylactically pass through the animal and enter the environment through irrigation with beef runoff wastewater (WW). There are concerns repeated low-level AM loading of soils through irrigation will alter the natural biota resulting in increased resistance; thereby, making AM critical for human and animal health less effective.
What Did We Do?
Several studies are summarized describing a cost-effective removal process of AM from beef wastewater before being applied as irrigation. Study 1 investigated three radiolabeled AM, ([14C]-erythromycin (ERY), [3H]-chlortetracycline (CTC), and [3H]-monensin (MON)) to quantify their partitioningin the aqueous and solids fractions of a beef wastewater (WW) containing suspended solids (SS). Following this, several flocculants were evaluated for removing SS with sorbed AM from WW. Study 2 evaluated the sorption properties of tylosin (TYL) with diatomaceous earth (DE) added to WW as a binding agent. Study 3 evaluated the proposed treatment process using pre-treatment of WW with flocculants then adding a binding agent to remove aqueous phase AM before being used an irrigation water.
What Have We Learned?
Study 1) After 48 hours, more ERY sorbed to the SS fraction than the aqueous. CTC partitioning occurred in three phases: a rapid sorption to the SS fraction between 0.5 and 8 hours with desorption into the aqueous fraction at 24 hours followed by short steady state at 48 hours with further desorption at 96 hours. The most lipophilic antibiotic, MON, quickly sorbed into the SS fraction and remained in equilibrium with the aqueous fraction after 48 hours. Calculated partitioning coefficients, Kd, for WW were very different from published soil-water values illustrating wastewater uniqueness. A follow up study determined alum and ferric chloride removed some ceftiofur (CEF) and chlorotetracycline (CTC); however, they were ineffective for removing TYL. Therefore, a process was needed to remove aqueous phase AM (figure 1). Study 2 evaluated three DE sources for binding aqueous TYL in WW. Raw (DER) contained organic carbon (OC) (3% g g-1), clays (20%) and amorphous silica (65%). Kieselguhr (DEK) had no OC (<1% g g-1), no clay (2%) and amorphous silica (96%). had nearly 3.5 times greater maximum sorption capacity when compared to DEK. Sorption of TYL to DEK and DER at different pH values showed cationic and hydrogen bonding interactions are important. Higher sorption of TYL to DER compared to DEK suggested clays-DE matrix was important for TYL sorption. Removing OC improved TYL sorption and decreased the separation time for DE/AM removal to complete treatment. Study 3 found CEF and CTC would bind to DE in controlled, neutral aqueous solution. When AMs were spiked into WW collected from a beef feedlot runoff pond, DE successfully removed TYL and CTC, but not CEF. Wastewater treated with excess alum to remove SS followed by DE treatment showed similar removal rates for TYL. Pretreatment of water with alum also resulted in CEF removal if larger amounts of DE are needed. The reason for change in CEF binding when pretreated WW with alum is still under investigation. Alum treatment appeared to remove most of the CTC spiked into WW and therefore no assessment of how CTC binding to DE after treatment.
Future work will include: evaluating the proposed treatment process on other AM and their metabolites. Development of modified DE matrices specific for non-polar AM and metabolites. These matrices could be combined to remove both polar and non-polar contaminants. Finally, the process needs to be evaluated for effectiveness of contaminant removal with municipal wastewater treatment systems.
Bryan L. Woodbury, Agricultural Engineer, USDA-U.S. Meat Animal Research Center, Clay Center, NE
Bobbi S. Stromer, Chemist Post Doc., USDA-U.S. Meat Animal Research Center, Clay Center, NE
Clinton. F. Williams, Lead Soil Scientist, USDA-US Arid-Land Agric. Research Center, Maricopa, AZ.
Katherine A. Woodward, Ph.D. Candidate, Tufts University, Civil & Environmental Eng., Medford, MA
Heldur Hakk, Research Chemist, USDA-Edward T. Schafer Agricultural Research Center, Fargo, ND.
Sara Lupton, Research Chemist, USDA-Edward T. Schafer Agricultural Research Center, Fargo, ND.
Stromer, B.S., B.L. Woodbury and C.F. Williams. 2018. Tylosin sorption to diatomaceous earth described by Langmuir isotherm and Freundlich isotherm models. Chemosphere. 193:912-920.
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