Background: Anaerobic digestion is a technology applied successfully
to converting organic matter into biogas. However, the presence of
inhibitory compounds such as antibiotics can adversely affect methane
production. The aim of this study is to evaluate the toxic effect of
chlortetracycline hydrochloride (CLOR) on the methanogenic bacteria. In
order to study the methanogenic toxicity of CLOR, different
concentrations of CLOR (10, 50, 100, 200 mg L 121) were evaluated
by methanogenic toxicity assays using three feedings. Results:
Maximum methane production was obtained for the assays with 10 mg CLOR
L 121, the values obtained were 277 \ub1 4.07; 193 \ub1 11.31
and 166 \ub1 7.07 mL for the first, second and third feedings,
respectively. The average values for acetic, propionic and butyric acid
at start of the experiments were 2104 \ub1 139; 632 \ub1 7.6; 544
\ub1 26 mg L 121, respectively. The VFA values obtained finally
of the experiment were dependent on the evaluated antibiotic
concentrations, indicating that the efficiency of methanogenesis is
directly affected by the CLOR concentration. Conclusions: CLOR is an
effective methanogenic bacteria inhibitor. Moreover, the results show
that CLOR has a bactericidal effect on methanogenic activity given that
methane production did not recover during the third feeding. This study
shows that the 50% inhibitory concentration (IC50) for methanogenic
bacteria in 10 mg L 121