| Nitrotoluene compounds are very important chemicals. They have teratogenic, mutagenic and carcinogenic effects on organisms. They are difficult to be oxidized due to the strong electron-withdrawing effect of the nitro group and are recalcitrant under natural conditions. Nitrotoluene wastewater has features of strong toxicity, high concentration, deep color and complex component. The reductive transformation of nitrotoluene compounds by zero-valent iron is an effective way to eliminate such pollution, and the resultant products could be easily used by microorganism. The reductive transformation of nitrotoluene wastewater by zero-valent iron could decrease toxicity and improve biodegradability. However, oxidation and agglomeration of zero-valent iron led to the decreasing of contact area and reduction efficiency and still cannot be avoided.In this study, the packing was made of iron, fly ash and kaolin in order to reduce the loss of zero-valent iron and improve the reduction efficiency of nitrotoluene compounds. nitrotoluene compounds were transformed into toluidine compounds by new iron-fly-ash packing, and toluidine was completely degraded by p-aminotoluene-tolerant and salt-tolerant sludge. The purpose of this study was to investigate the effect of reaction condition on reductive transformation of nitrotoluene compounds and compare the performance of Fe, Fe/Cu bimetal system, the iron-activated-carbon packing and the iron-fly-ash packing. After the p-aminotoluene-tolerant and salt-tolerant sludge was acclimated, and toluidine was completely degraded. The purpose was to investigate the effect of reaction condition on mineralization of toluidine and reveal the community diversity and structure at different acclimated stages by high-throughput sequencing. The main experimental results were as follows:The results showed that the reductive transformation of 4-nitrotoluene followed pseudo-first order reaction, p-aminotoluene was the reduction product of 4-nitrotoluene. Low pH, low concentration of p-nitrotoluene and high dosage of packing could improve the reduction efficiency. It was obvious that there was competition between 2-nitrotoluene and 4-nitrotoluene in the same solution. The reductive transformation reaction of 4-nitrotoluene was ahead of 2-nitrotoluene. In order to solve the problem of competition, the mixed solution was adjusted under low pH level. Compared with Fe, Fe/Cu bimetal system and the iron-activated-carbon packing, the performance of the iron-fly-ash packing was the best. The reduction efficiency could remain at around 50% in 40 days. New iron-fly-ash packing had obvious advantages in reduction efficiency, manufacturing costs and environmental pollution.The results of SEM-EDS and XRD showed that the composition and morphology of iron-fly-ash packing greatly changed before and after reaction. The surface of packing was smooth, and no oxidation occurred on the surface before reaction. However, the surface of the packing became rough after 40 days of operation. It was evident that Fe decreased apparently, C increased slightly and O aggrandized evidently by EDS. XRD shows that the corrosion product of Fe was FeO(OH).p-Aminotoluene was completely biodegraded by p-aminotoluene-tolerant and salt-tolerant sludge. pH, salinity, concentration of sludge and concentration ofp-aminotoluene were the main influencing factors for the biodegration of p-aminotoluene. The samples of sludge were analyzed by high-throughput sequencing technology. Compared with without acclimation, the richness and diversity of bacteria gradually reduced, but the percentage of salt-tolerant bacteria apparently increased. At phylum level, Proteobacteria and Bacteroidetes were prominent organisms in the p-aminotoluene-tolerant and salt-tolerant sludge. Gammaproteobacteria, Flavobacteriia and Betaproteobacteria occupied higher percentages at class level. Chryseobacterium and Sphingobacterium were core genus at genus level. The gene of "Membrane transport" accounted for a larger proportion. |
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