Effects of nitrophenols on acetate utilizing methanogenic systems

Nitrophenols are widely used for manufacturing explosives, pharmaceuticals, pesticides, pigments, dyes, etc. A literature research shows that there is a lack of quantitative information on the effects of nitrophenols on anaerobic systems. The objective of this research was to study the toxic effects of nitrophenols on acetate enrichment, methanogenic systems. Anaerobic toxicity assays were performed with batch serum bottles. Results showed that among the selected nitrophenols, toxicity decreases in the following order: 2,4-dinitrophenol > 4-nitrophenol > 2-nitrophenol > 3-nitrophenol. Complete removals of mononitrophenols were seen in serum bottle systems which did not fail due to toxicity. Chemostats (15-day retention time) were used to study toxicity, acclimation, and removal of 4-nitrophenol in continuous systems. New steady-states with high effluent acetate (substrate) concentrations were attained after spiking 5.5, 13.5, and 33.0 mg 1−1 of 4-nitrophenol. A competitive inhibition coefficient model fits well with the experimental data from 4-nitrophenol studies. The competitive inhibition coefficient K1, for 4-nitrophenol varied between 0.077 and 0.089 mg 1−1. Fifty-five to 82% of the 4-nitrophenol was removed in the chemostats; HPLC analysis of effluents showed no intermediate products.