| Recently, heterogeneous Fenton- like oxidation technology as a typical advanced oxidation treatment has been attracted widespread attention. It has the advantages of efficient, mild reaction conditions, and simple equipment. Especially bimetallic heterogeneous Fenton- like system shows synergistic effect between the metal ions, which can increase the activity of catalyst. However, this techonology will meet some problems in practical application. Firstly, the important issue is finding a suitable carrier for the active catalyst. Secondly, Fenton reactions solely used for complete mineralization of organic pollutants may be expensive. Therefore, the combinations of heterogeneous Fenton- like reactions and biological oxidation for treatment of industrial wastewater are significance for promoting the Fenton technology. The stability of the system can be improved, and the processing cost of wastewater can also red uce. Unlike the homogeneous Fenton reactions, due to the presence of catalysts in heterogeneous Fenton- like systems, heterogeneous Fenton- like catalysts may affect the post- treatment biological treatment unit if the catalyst flows into the post-treatment reactor.Therefore, in the paper, the bimetallic heterogeneous Fenton- like catalyst was first prepared by homogeneous precipitation method. Then the removal efficiency and influence factors were analyzed for treatment reactive brilliant blue and rhein. Meanwhile, the degradation mechanis m and degradation pathway of reactive brilliant blue and rhein by heterogeneous Fenton- like were proposed. Meawhile, the apparent kinetic models were established. Influence on sludge characteristics and microbial community of tradit ional Chinese medicine wastewater containing rhein before and after pretreatment by heterogeneous Fenton- like system was investigated, which could realize good combination of heterogeneous Fenton- like and biological treatment technology.The optimal conditions were found for preparing bimetallic heterogeneous Fenton- like catalyst by Box- Behnken experiment, which were as follows: concentration of Fe（NO3）3, Mn SO4 and urea were 0.18mol/L, 0.05mol/L, and 1.0mol/L, respectively. The dosage of the modified sepiolite was 40g/L and water bath temperature was 100℃. Additionally, the catalyst was calcined at 370 ℃ for 3h. The iron concentration is 2 0.2wt%, and the manganese concentration was 3.12wt%. The catalyst showed the characteristic diffraction peaks of α-Fe2O3 and γ- Fe2O3. After 6 cycles of repeated used, 70% percentage of reactive brilliant blue was still be oxidized, suggesting the stable performance of the catalyst in application.A four factor central composite design（CCD） coupled with response surfa ce methodology（RSM） was applied to evaluate and optimize the important variables. When the reaction conditions were catalyst dosage=0. 70g/L, H2O2=0.72 m L/L, pH=3.12, [reactive brilliant blue]o=60mg/L, at room temperature, the decolorization efficiency of reactive brilliant blue was 88.68% within 60 min. Meanwhile, when the reaction condit ions were catalyst dosage=0.78g/L, H2O2=0.38 m L/L, pH=3.53, [rhein]o =20mg/L, the removal efficiency of rhein was 97.62% within 60 min.At the initial pH of acidic condition, the ·OHabs on the surface of the catalyst and the solut ion of ·OHfree were the reactive oxygen species. However, when the pH value was 5.0-6.0, the ·O Habs on the surface of the catalyst was given priority. At first, hydroxyl free radicals were attacked nitrogen to hydrogen bond, triazine group, and anthraquinone structure of the reactive brilliant blue and rhein. Then, phthalic acid and benzoic acid were produced, and they were degraded into small molecules carboxylic acid such as butyric acid, oxalic acid, acetic acid, and so on. At last, the short-chain acids were converted into CO2 and H2 O. When hydroxylamine and ascorbic acid in the solution, the transformation of ferrous ions into iron ion was facilitated, thus increasing hydroxyl free radical generation. Therefore, they could improve treatment efficiency. It had no obvious influence of the existence of SO42-on degradation of reactive brilliant blue and rhein by heterogeneous Fenton- like. There was different degrees restraint of HCO3-, CO32-, H2PO4-, and HPO42- passing on oxidation ability of the heterogeneous Fenton- like reagent. HCO3- accelerated the inefficient decomposing of H2O2. Phosphate existed in the form of H2PO4-which would react with ferrous and ferric ions to form the complex compounds. CO32- had a strong ability to capture ·OH. And HPO42- could inhibit H2O2 decomposit ion.The adsorption processes of reactive brilliant blue and rhein on the catalyst were correlated well with the Langmuir isotherm model. The value of Ea, 38 k J/mol and 36.44KJ/mol for heterogeneous Fenton- like indicated that the process was controlled by apparent. At the same time, the positive value of ΔH, 36 k J/mol and 33.87KJ/mol for heterogeneous Fenton- like indicated that the process was endothermic. The apparent kinetic models of degradation reactive brilliant blue and rhein by heterogeneous Fenton- like were V=0.031×P0.29×F0.23×E0.79, and V=0.032×P0.55×F0.29×E0.86, respectively. P was the concentration of reactive brilliant blue or rhein. F was catalyst dosage. E was H2O2 dosage.Rhein had physiological toxicity for methanogens. When rhein（>20mg/L） entered into the double circle（DC） anaerobic reactor, the methane production rate was only 0.06m3CH4 /kg CO D. The particle size distributions（PSD） of granular sludge in the second reaction area were 27.61μm, 76.26μm for surface area average diameter and volume average particle size, respective ly. The integrity coefficient（IC） value increased to 37.8. The amine absorption peak of the EPS（extracellular polymeric substances） changed from blunt peak to sharp peak, and the polysaccharide absorption peak was a bimodal in fourier transform infrared（FTIR） spectra. The methane bacteria species was not predominant in the microbial community. Thermoprotei phylum became predominant species. After pretreatment, the average COD removal rate was 94% and the average methane production rate reached to 0.33m3CH4 /kg CO D. The volatile fatty acid（VFA） was no obviously acclumation in the effluent. Methanobacteriaceae and Methanomicrobiaceae became predominant species in the anaerobic granular sludge.When the catalyst was added into the bioreactor, it had no significant impact on the performance of anaerobic granular sludge. Sepiolite was magnesia silicate and the catalyst could provide iron and manganese ions. Therefore, it made anaerobic granular sludge particle size bigger, density larger, and greater mechanical strength. The concentrations of EPS changed from 83.7mg/g VSS to 89.1mg/g VSS. It was noted that the EPS content increased with the presence of the catalyst. It could better safeguard the stability and settleability of granular sludge. Although the number of Methanosaetaceae and Methanobacteriaceae in the anaerobic sludge changed, they were still the dominant species. The abundance of Methanosaetaceae was 70.5%, while that of Methanobacteriaceae was 21.8%. Therefore, the combination technology of heterogeneous Fenton- like and biological treatment could be used to treat difficult degradable industrial wastewater. It could not only improve the application range of heterogeneous Fenton- like technology, but also the stability of treatment was guaranteed. |
