Semi-empirical Approach on the Methanogenic Toxicity of Aromatic Compounds on the Biogas Production

In this work, a semi-empirical approach correlating the values of methanogenic toxicity of 22 aromatic compounds was used.  TheIC50 exp, along with the various molecular properties of these compounds were determined using the DFT B3LYP/6-31G (d,p) method. While a conceptual approach of the FDT, was made in order to determine those, which are responsible of this methanogenic activity of the studied aromatic compounds. The Principal Component Analysis method was used in order to describe all the connections and information contained between these various variables (IC50exp.and molecular properties) of the aromatic compounds. TThe Hierarchical Cluster Analysis helped to classify the studied aromatic compounds in various classes defining the various types of methanogenic toxicity. The findings show that the electron withdrawing and lipophilic substituents made the aromatic ring more toxic than the electron donating and hydrophilic substituents.The aromatic compounds with -NO2 and –Cl groups formed the classes of the most toxic with the bactericidal action ofstudied aromatic compounds, with values of IC50exp ranging between 4.19 ± 0.01 and 67.20 ± 1.97 mg/L. The compounds with -OH and -NH2 groups formed the class of the least toxic of studied aromatic compounds with bacteriostatic action with values of IC50exp ranging between 966.27 ± 7.04 and 3151.49 ± 5.93 mg/L. The benzene (aromatic ring unsubstituted) taken as reference, formed its own class with a value of IC50exp of 208.78 ± 2.80 mg/L. It thus marks the line of demarcation between the classes of studied aromatic compounds with the electron withdrawing and/or lipophilic substituents  (-NO2 and -Cl), more toxic with the bactericide action, and that of the aromatic compounds with electron donating and hydrophilic substituents (-OH and -NH2), less toxic with the bacteriostatic action.