The Biodegradation Of Nitropenols In Wastewater

Along with the development of chemical industries, many recalcitrant organic chemicals have been discharged into natural environments together with wastewaters and can exist in waters, soil and sediments for a long time without degradation. These hazardous substances, their byproducts and metabolites can be highly toxic, mutagenic and carcinogenic, thereby threatening animals, plants and human health through food chain. Consequently the removal of these compounds is of significant interest in the area of wastewater treatment. Nitrophenols are among the most important toxic and refractory substances. They are widely used as raw materials or intermediates in the manufacture of explosives, pharmaceuticals, pesticides, pigments, dyes, wood preservatives and rubber chemicals. The U.S. Environmental Protection Agency has listed 2-nitrophenol, 4-nitophenol and 2,4-dinitrophnol as "Priority Pollutants".The literature survey indicates that understanding about the biodegradation of nitrophenols is far from complete and more information is required on following problems. (1) Because of the complexity of biological metabolites, the study results on the toxicity and degradability of nitrophenols in aerobic and anaerobic treatment systems were different and even contrary. (2) Previous works on the biodegradation of nitrophenols and their metabolic pathway are mainly related to the development of pure cultures and mixed cultures in flasks. Few papers have dealed with the engineering aspects of continuous process. (3) There is a lack of information on the biodegradation kinetics of nitophenols. (4) The anaerobic metabolic pathways and mechanisms of some nitrophenols have not been discovered.In this paper the biodegradability and toxity of nitrophenols in aerobic and anerobic conditions are evaluated using different tests. The extensive efforts have been made to investigate the feasibility of effective removal 3-nitrophenol and 2,6-dinitrophenol in synthetic wastewater using laboratory-scale UASB reactors. The biodegradation kinetics of 3-nitrophenol, 2,6-dinitrophenol and 2,4-dinitrophenol were also studied in batch anaerobic bottles and aerobic sequencing batch reactors. The main...