Toxicity and degradability of nitrophenols in anaerobic systems

Nitrophenols are among the most important and versatile industrial organic compounds and are widely used in the chemical industry and are listed as priority pollutants by the U.S. EPA. The toxic effects and degradability of three selected nitrophenols (2-nitrophenol, 4-nitrophenol and 2,4-dinitrophenol) in anaerobic acetate and propionate enrichment systems were studied using batch serum bottles. The toxicity to both propionate- and acetate-fed systems decreased in the following order: 2,4-dinitrophenol > 4-nitrophenol > 2-nitrophenol. An up-flow fixed film, acetate-fed reactor was able to acclimate to 20 mg/L of 2- and 4-nitrophenol showing a 95% removal of each nitrophenol. The effect of biomass was studied using serum bottles for anaerobic toxicity assays with the design volatile suspended solids (VSS) concentrations of 500, 1000, and 1500 mg/L. With higher VSS the toxic effects of nitrophenols on methanogenesis were less severe. Nitrophenols were more inhibitory to acetate utilization than propionate utilization. Under anaerobic conditions, 2-nitrophenol and 2,4-dinitrophenol were transformed both abiotically and biotically to 2-aminophenol and 2-amino,4-nitrophenol, respectively. The presence of propionate in propionate enrichment culture enhanced the removal rates of all three nitrophenols studied.