Effects of short-term inhibition of Tetracyclines and Macrolides on specific methanogenic activity and swine biodegradability

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Limited studies have examined kinetic models related to the impact of antibiotics on acetoclastic methanogenesis and swine wastewater biodegradability, which can be useful for improvement and correct operation of anaerobic systems. Many researchers have evaluated the inhibition on this main methane-producing pathway by antibiotics individually but in rare cases as a mix. Thus, two tetracyclines: oxytetracycline (OTC) and tetracycline (TCN) and one macrolide: tylosin (TYL) were used separately and in combination OTC+TCN+TYL (MIX) to evaluate their inhibition effects. Short-term inhibition assays are useful to evaluate the antibiotics impact detected on swine wastewater specific methanogenic activity (SMA) and biodegradability (BD) at different concentrations of antibiotics (15, 30 and 45 μ g/mL); OTC and MIX showed the highest inhibition on SMA (78 and 76%, respectively) while the lower one was on methane production at 45 μ g/mL of MIX (61%). The assays with swine wastewater showed that OTC and TCN had the highest inhibition on BD at 45 μ g/mL, 71 and 51%, respectively. As expected, the maximum decrease in methane production (43.0% and 56.0%, respectively) occurred in the assays with the highest OTC and MIX concentrations, while TYL did not impact methane production in all assays. In specific activity, the results showed half-maximal inhibitory OTC concentrations (3.8 and 2.8 μ g/mL) in SMA and BD assays, respectively, while OTC recorded in methane production 4.5 and 54 . 2 μ g /mL in SMA and BD assays, respectively. These results indicate that antibiotics affect specific methanogenic activity and biodegradability more than methane production and inhibition was proposed as uncompetitive. • SMA is 80% inhibited when OTC concentration is up to 45 μ g/mL. • Combined toxicities of antibiotic MIX present a highest negative synergistic effect. • The propose kinetic model describe the inhibition of OTC, TCN and TYL on SMA and BD. • The observed effect of antibiotics was compatible with uncompetitive inhibition.