Effects Of Different Co-substrates On Degradation Of Nitrophenols Using Upflow Anaerobic Sludge Bed(UASB)Reactors

In this thesis the removal efficiencies of 3-nitrophenol (3-NP) and 2,6-dinitrophnol (2,6-DNP) are investigated in two lab-scale upflow anaerobic sludge bed (UASB) reactors using two different co-substrates. Degradation and transformation of nitrophenols are studied consequently. The effect of nitrophenol rate, input co-substrate concentrations and hydraulic retention time (HRT) to the degradation of nitrophenol and chemical oxygen demand (COD) as well as the operation of UASB are investigated with different co-substrates. At the same time, the special distribution of nitrophenol, aminophenol, COD, volatile fatted acid (VFA) and alkalinity along the UASB reactor are investigated. The characteristics of anaerobic granules before and after experiment are also compared. The major conclusions follow below.(1) Glucose is found to be a better co-substrate for 3-NP degradation as compared to sodium acetate. While for the degradation of 2,6-dinitrophenol, sodium acetate is better.(2) Throughout the study of 3-NP anaerobic degradation, input COD concentration are kept constant as 2500mg/L. Hydraulic retention time (HRT) is kept as 26h with glucose as co-substrate. Maximum 3-NP concentration is 254.6mg/L, almost all of the 3-NP can be removed. While input 3-NP concentration is below 100mg/L, 3-AP conversion is stably 60%, a little of 3-AP has been transformed. But 3-AP can't be transformed any more while input 3-NP concentration is 250mg/L. A majority of 3-NP and COD are removed at 20.5cm depth. While HRT is 30h with sodium acetate as co-substrate, maximum 3-NP concentration is 71.6mg/L and 3-AP conversion is invariable through the experiment. The 3-NP and COD removal effects with glucose as co-substrate are better than them with sodium acetate as co-substrate at 20.5cm depth.(3) Input co-substrate concentrations have obvious effect to the degradation of 3-NP and transformation of 3-AP when input co-substrate concentrations decrease gradually. In the decrease of input co-substrate concentrations experiment, when input glucose concentrations are above 606mg/L, output 3-NP concentrations are almost stable, 3-NP removal are always above 99%, 3-NP removal proportion occupies more than 97% of the whole input 3-NP at 4cm depth. With the decreasing of input glucose concentrations, when input glucose concentration is about 284mg/L, only half of the input 3-NP can be removed. During the process of this experiment, 3-AP can't be removed basically any more. With the decreasing of the sodium acetate concentration during the whole experiment, 3-NP removal efficiencies are as much as the efficiencies with glucose as co-substrate. Along with the touching time between 3-AP and anaerobic microorganism, the transformations of 3-AP increase gradually. Throughout the space distribution of 3-NP, it can be investigated that the velocity of 3-NP degradation is faster with glucose as co-substrate.(4) In the experiment of decreasing HRT, there is a good 3-NP removal effect while HRT≥16h with glucose as co-substrate. 3-AP transforms a little. The 3-NP removal efficiencies in the whole reactor are all above 95% and 3-NP is removed mostly at 4cm depth. While HRT is shortened from 30h to 12h gradually with sodium acetate as co-substrate, also, there is a good 3-NP removal effect. The 3-NP removal efficiencies are decreased to 91.6% as the HRT is decreased to 8h. With sodium acetate as co-substrate, decreasing HRT has an obvious influence for 3-AP transformations, 3-AP transformed little and little. There is a better effect at the same depth with glucose as co-substrate compared to sodium acetate as co-substrate.(5) For the study of 2,6-DNP degradation, input COD concentration and HRT is respectively kept about 2500 mg/L and 35h with glucose as co-substrate, the maximum 2,6-DNP concentration is 170.0mg/L. Throughout the whole experiment, COD and 2,6-DNP removal efficiencies are kept above 85.0% and 98.0% respectively. At 20.5cm depth, most of input COD and 2,6-DNP can be removed. At 95.5cm depth, COD removal efficiencies is stably kept about 90.0% and 2,6-DNP removal efficiencies is above 97.5%. While HRT is kept 30h with sodium acetate as co-substrate, maximum 2,6-DNP concentration can be increased to 189.5mg/L and 2,6-DNP removal efficiencies are better than it with glucose as co-substrate. Throughout the space distribution of 2,6-DNP, it can be investigated that the velocity of 2,6-DNP degradation is faster with sodium acetate as co-substrate.(6)In the experiment which is compared characteristics of anaerobic granules before and after experiments, it can be found the phenomenon below: Before the experiment, the granules which particle size is more than 2 mm occupied both more than 85% of the whole granules. The granules are affected by toxicity of the nitrophenols and big granules are destroyed greatly. So some big granules are broken to the small ones. The granules which particle size is more than 0.5 mm only occupy 40% or so. At the same time, the methanogenic activities are greatly decreased after the experiment.