Study On The Anaerobic Biodegradability And Toxicity Of Xenobiotic Nitrophenols

In this study, the anaerobic biodegradability and toxicity of five nitrophenols are evaluated by measuring correlative indexes in anaerobic batch assays. At the same time, granular sludge which has good degrading effects is cultivated and acclimated successively in two UASB reactors by using man-made nitrophenol wastewater, and the reactors' different running conditions are studied. The following achievements are obtained.(1) Anaerobic biodegradability test demonstrates that three mono-nitrophenols (ortho-, meta-, para-) can be decomposed finally in anaerobic conditions after being acclimated, but 2,4- and 2,6-dinitrophenols have rather stronger inhibitions to the methanogenic bacteria. The anaerobic biodegradability order to decrease is 2-nitrophenol. > 3 -nitrophenol >4-nitrophenol> 2,6-dinitrophenol > 2,4-dinitrophenol.(2) Anaerobic toxicity assay demonstrates that when the concentration of nitrophenols is higher, the inhibition level is better. In the range of experimental concentrations (<24mg/L), 2-nitrophenol can cause stimulated action, but 3- and 4-nitrophenol can cause slight and middle inhibition respectively. For 2,4- and 2,6-dinitrophenol, they can produce stimulation in lower concentrations but middle and slight inhibitions in higher one respectively. The inhibition order to decrease is 2,4-dinitrophenol > 2,6-dinitrophenol >3-nitrophenol>4-nitrophenol >2-nitrophenol.(3) Methanogenic activity resuming test indicates that the toxicity of three mono-nitrophenols is metabolic in lower concentrations (<10mg/L) but physiological when the concentration is increased. For 2,4- and 2,6-dinitrophenol, the toxicity is physiological and metabolic respectively in lower concentrations (<5mg/L), but bactericidal and physiological respectively in higher ones.(4) The test of granular sludge's continuous cultivation and acclimation in UASB indicates that the gained types of sludge and microbial culture are almost identical. Thegranules resemble C type which is tight sphericity and mainly consists of Methanosarcina when the cultivation is just finished and A type which is mainly comprised by Methanothrix and Methanoformicicum after acclimated period ends, and the latter is probably transformed by the former.(5) After acclimation is finished in UASB, the two reactors can operate steadily while influent COD concentrations are changed. When HRT is changed, the reactors will be operating unstably at first but will resume soon, which indicates that the load increasing of nitrophenols has caused inhibition to anaerobic microbes, but the COD removal isn't influenced evidently in the long test period. So the bacterial culture hi the sludge has formed enzyme system that can metabolize the organic compounds of containing nitrophenols waste water. The reactors can operate with good treating effects and can endure strike loading's variation.