Submitted to: Journal of Applied Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/25/2012
Publication Date: 3/20/2012
Citation: Varel, V.H., Wells, J., Shelver, W.L., Rice, C., Armstrong, D.L., Parker, D.B. 2012. Effect of anaerobic digestion temperature on odour, coliforms and chlortetracycline in swine manure or monensin in cattle manure. Journal of Applied Microbiology. 112:705-715. Interpretive Summary: Pharmaceutical compounds fed to livestock are known to be excreted in manure along with coliforms, and potentially can have a negative consequence on the environment. Antibiotics may affect aquatic and terrestrial organisms, and develop antibiotic resistance in microorganisms. Coliforms can contaminate water and food products. Manure from swine fed chlortetracycline or cattle fed monensin was added to 2-liter methane digesters at 22, 35, and 55°C and evaluated as a manure treatment method to degrade the antibiotics chlortetracycline or monensin, and eliminate coliforms in the manure. The lowest temperature, 22°C was not effective in eliminating either of the antibiotics or the coliforms after 25 or 28 days. The highest temperature, 55°C eliminated all coliforms within one day, and 98% and 27% of the chlortetracycline and monensin, respectively. The intermediate temperature, 38°C, eliminated all coliforms in the swine manure by day 3, and degraded 80% of the chlortetracycline after 25 days. In the cattle manure, 38°C eliminated all coliforms by day 14, but only 7% of the monesin was degraded. These studies suggest 55°C anaerobic digestion of livestock manure can be used to eliminate coliforms from swine and cattle manure, and significantly reduce the concentration of chlortetracycline in manure. However, monensin is much more resistant to degradation. Thus, livestock producers need more information on which pharmaceutical compounds are degraded by various manure treatments, whereby they can make better decisions on the prudent use of antibiotics in their production environment.
Technical Abstract: Antibiotics used in animal feeding operations have been detected in the environment. There is a growing concern about the impact of these pharmaceutical compounds in the manure and the effect they may have on aquatic and terrestrial organisms, and the potential development of antibiotic resistant microorganisms. This study evaluated the effect of anaerobic digestion at 22, 38, and 55ºC on odor, coliforms, and chlortetracycline (CTC) in swine manure or monensin (MON) in cattle manure. Swine or cattle were fed the respective antibiotic, manure was collected, and 2-L laboratory methane digesters were established at the various temperatures. Once the methane digesters were acclimated to the manure substrate and temperature, three replicate digesters at each temperature with either swine or cattle manure were set up and analyzed periodically over 25 or 28 d. A separate 150 mL serum bottle containing 50 g of manure representing each digester was used to analyze biogas volume and composition. After 21 d, the concentration of CTC in the 22, 38, and 55ºC swine digester slurries decreased 7, 80, and 98%, respectively. Coliforms in the 22ºC digester slurries were still viable after 25 d; however, they were not detectable in the 38 and 55ºC slurries after 3 and 1 d, respectively. After 28 d, the concentration of MON in the 22, 38, and 55°C cattle digester slurries decreased 3, 8, and 27%, respectively. Coliforms in the 22ºC cattle digester slurries were still viable after 28 d; however, they were not detectable in the 38 and 55ºC slurries after 14 and 1 d, respectively. These studies indicate that anaerobic digestion of swine manure at 38 or 55ºC may be an effective treatment to reduce CTC and coliforms. However, anaerobic digestion of manure is not an effective treatment to reduce MON that may be in cattle manure. Assuming it is feasible and one can obtain the desired response, a livestock producer may want to consider using an antibiotic that is susceptible to degradation by a specific manure treatment to prevent negative environmental consequences.