Comparative Study of Benzenediols, Methylphenols and Chloroanilines Isomers on the Inhibition of Acetoclastic Methanogenesis By Digested Pig Manure Methanogenic Archaea

Aims: The present work aims to study the effect of aromatic structure on the inhibition of biogas biosynthesis, and more specifically the comparative study of benzenediols, methylphenols and chloroanilines isomers on the inhibition of acetoclastic methanogenesis by digested pig manure methanogenic archaea. The objective of this study was also to examine the structure-toxicity relationships of aromatic compounds to acetoclastic methanogens. The ultimate goal is the modeling of the influence of the aromatic structure on the inhibition of methane biosynthesis.

Study Design: Anaerobic digestion of pig manure, anaerobic toxicity essay, Effect of the isomerism (functional groups position) on the methanogenic toxicity, Correlation of the methanogenic toxicity with aromatic compounds hydrophobicity (logPoct),

Place and Duration of Study: Department of Chemistry, University of Kinshasa, DR Congo, between January 2011 and March 2012.

Methodology: The toxicity to acetoclastic methanogenic archaea 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 obtained results indicate that relationships exist between the isomerism of cresols, benzediols (catechol, resorcinol, and hydroquinone) and chloroanilines; and their inhibitory effects on methanogenic archaea. The toxicity of Cresols, benzenediols and reference compounds increases, respectively, in the following order: Benzenediols < Phenol < Cresols. The grafting of methyl (-CH3) at phenol to form cresols, make cresols to be more toxic than phenol. Secondly, by adding a hydroxyl group (-OH) at phenol to form benzenediols, these compounds become less toxic than phenol. The grafting of chlorine (-Cl) at aniline to form chloroanilines, make chloroanilines to be more toxic than aniline. And secondly, by adding an amino group (-NH2) at chlorobenzene to form chloroanilines, these compounds become less toxic than Chlorobenzene. For the three isomers studied in this work, ortho is the most toxic followed by meta while para is always the less toxic.

A high significant linear correlation between the toxicity of cresol, benzenediols and chloroanilines isomers and reference aromatic compounds and their hydrophobicity (R2 = 0.9278) was found.

Conclusion: The results obtained in this paper indicate that it exist a correlation between the isomerism (chemical structure) of Cresols, benzendiols, chloroanilines and their inhibitory effects on methanogens. Hydrophobicity of a compound as indicated by logPoct is directly related to the partition of a compound into archaeal membrane.