ABSTRACT
The present paper aims to study the effect of aromatic structure on the inhibition of biogas production and more specifically the effect of para substituted anilines functional groups (chemical structure) on methane biosynthesis by the digested pig manure methanogens. The objective of this study was also to examine the structure-toxicity relationships of aromatic compounds to acetoclastic methanogens. Study Design: Anaerobic digestion of pig manure, anaerobic toxicity essay, The effects of functional group nature on inhibition of methane production by acetoclastic methanogens. Correlation of the methanogenic toxicity (IC50) with aromatic compounds hydrophobicity (logPoct). Place and Duration of Study: Department of Chemistry, University of Kinshasa (DR Congo), between August 2011 and May 2012. Methodology: The toxicity to acetoclastic methanogenic bacteria was performed with the standard method of serum bottles, digested pig manure was utilized as inoculums, acetate as substrate and the methane gas volume produced was measured by serum bottles liquid displacement systems (Mariotte flask system). Results: The obtained results indicate that relationships exist between para substituted anilines functional groups nature (chemical structure) and their inhibitory effects on methanogens. The toxicity of para bisubstituted anilines increases in the following order: SO3 < OH < H < CH3 < Cl < NO2 From this sequence of increasing toxicity, it can be seen that the methanogenic toxicity varies with the functional group nature which is in the para position of the main function. Indeed, p-Nitroaniline and benzene with 45.76 and 208.78 mg/l as IC50 values respectively were the most toxic compounds, while p-Aminophenol and p-Aminosulfonic acid (Sulfanilic acid) with 1800.39 and 2777.82 mg/l IC50 values were the less toxic. A very significant negative linear correlation between the toxicity of para substituted anilines compounds and their hydrophobicity was found. Conclusion: The results of this study indicate that relationships exist between para substituted anilines functional groups nature and their inhibitory effects in methane biosynthesis by the methanogens.