Effect of Para Substituted Anilines Chemical Structure on Methane Biosynthesis by the Methanogens.

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.

Inhibitory Effects of Phenolic Monomers on Methanogenesis in Anaerobic Digestion.

Aims: The purpose of this study was to evaluate the inhibitory effects of phenolic monomers on methanogenesis in anaerobic digestion and to assess the effect of hydroxyl groups’ number of phenolic monomers (aromatic structure) on inhibition of methane production by acetoclastic methanogens (archaea). Study Design: Anaerobic digestion of pig manure, anaerobic toxicity essay, The effect of the hydroxyl group’s number on the methanogenic toxicity as exhibited by monomeric tannins, Correlation of the methanogenic toxicity (IC50) with aromatic compounds hydrophobicity (logPoct), Correlation of the methanogenic toxicity (IC50) with Cresols boiling point (bp). Place and Duration of Study: Department of Chemistry, University of Kinshasa (DR Congo), between September 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 and acetate as substrate. The methane gas volume produced was measured by serum bottles liquid displacement systems (Mariotte flask system). Results: The results of this study indicate that an increase in the number of hydroxyl groups on the aromatic compound was associated with a decrease in the compound’s toxicity to methanogens (archea). The toxicity of various phenolic monomers are decreasing in the following order: pyrogallol < hydroquinone < resorcinol < phenol < benzene with 3172, 2745, 1725, 1249 and 209 mg/l IC50 values respectively. A significant negative linear correlation between the toxicity of phenolic monomers together with the reference compound (benzene) and their hydrophobicity was found. Moreover, a high positive linear correlation has been found between the IC50 values of phenolic monomers and their boiling temperatures. Conclusion: The obtained results indicate that relationships exist between the phenolic monomers structure and their inhibitory effects in methane biosynthesis. The analysis of experimental results suggests that an increase in the number of hydroxyl groups on the aromatic compounds was associated with a decrease in the phenolic monomers toxicity.