| The coal gasificationl wastewater (CGW) is a typical industrial wastewater characterized by high concentration of pollutants, bio-refractory and high toxicity. There are many problems such as fairly long hydraulic retention time, low processing efficiency, high cost, and COD and NH4+-N in effluent are difficult to meet the discharged standards in the traditional anaerobic-aerobic activated sludge biochemical system. In this paper, the biochemical system and Electro-Fenton integrated system was employed to treat the Lurgi CGW in Harbin gasification plant, and degradation properties were investigated. Chosen nitrogenous heterocyclic compounds (NHCs) as denitrification carbon in order to reveal the degradation behaviorof NHCs under anoxic condition.The treatment effect was investigated by comparison with AOAO and A2O2denitrifying biofilm system, and the results indicated that A2O2had a better pollutant removal at the same operation conditions. When HRT was72h and recycle ratio (R) was2, the maximum removal rates of COD, NH4+-N and TN, were94.4%,90.7%and80.77%, which average effluent concentration were150mg/L,11.6mg/L and51.5mg/L, respectively. For A2O2system, recycle ratio had a significant impact on nitrification effect, and the NH4+-N removal rate increased from about75%at R=1to90.72%at R=2, but decreased to80.31%at R=3. Batch test results showed that phenol could be used as high quality carbon source in the denitrification process, and could improve the anoxic biodegradability properties of NHCs (such as pyridine, pyrrole and imidazole) as the first matrix in co-metabolism.The biodegradability properties of phenol and some NHCs in CGW were further investigated in a continuous-running anoxic reactor. Under the optimal denitrification temperature of25℃, the maximum sludge removal loading rate (SLR) of phenol was8.15mg/(g MLSS-h), and the corresponding SLR of denitrification was5.34mg NO3-N/(g MLSS-h). SLR of pyridine as denitrification carbon source was4.38mg/(g MLSS-h) under anoxic condition, however, the start-up time of anoxic system was normally long. The start-up period could be shortened after phenol was introduced as co-substrate, which was due to the fact that the toxicity effect of pyridine on microbe was weakened. As the sole carbon source, the anoxic removal rates of quinoline and pyrrole were only18.5%and14.9%, respectively, and which increased to73.8%and65.9%when co-metabolished with phenol. Phenol has no effect on degradation of imidazole under anoxic condition, and the average removal rate was rarely24%. These results confirmed that placed anoxic zonein the most front of denitrification system could reinforce the removal of refractory organics, and reduce the pollutants load of follow-up processing.The removal efficiencies and degradation properties of organics and NH4+-N in CGW were studied in A2/O-MBR system. HRT, which decreased from72h to48h, had little effect on the removal efficiensies of organics and NH4+-N. This was one of the advantages of A2/O-MBR system. The activity of nitrifying bacteria was inhibited when recycle ratio was too high or low (R=6or R=1), and COD removal rate could also sharp decrease at R=1which was affected by the toxicity of phenol. The average removal efficiencies of COD, NH4+-N and TN under HRT of48h and R of3were97.4%,92.8%and74%, with final concentrations in the effluent were71mg/L,9.6mg/L and74mg/L, respectively. The composition and concentration of organics in every step were analyzed by GC/MS and it was found that anaerobic process (A1) could change the molecular structure of organics by reactions such as ring opening, chain scission, and to improve the degradation properties, although the removal of TOC was only12.8%. It also be found that MBR could remain stable operation for a long term due to the low membrane fouling rate under MLSS≤10g/L.In this paper, the activated carbon supported nano iron oxyhydroxide (AC/FeOOH) catalyst was prepared, characterized, and used in the advanced treatment of A2/O-MBR effluent by Electro-Fenton technology. The results indicated that FeOOH of the heterogeneous FeOOH/AC catalyst prepared by air oxidation of ferrous hydroxide (Fe(OH)2) suspension methodconsisted of goethite (α-FeOOH) and lepidocrocite (γ-FeOOH) mixed crystals. The effect of solution pH, H2O2dosage and electrolyzer voltage on the degradation efficiencies were investigated in detail and then the optimal operation parameters were determined. Under the optimal condition:pH=7.0,2.0ml H2O2/L and electrolyzer voltage of IV, COD removal rate was84.43%and the final effluent concentration was19.9mg/L after40min adsorption and90min catalytic oxidation.In summary, A2O2system was efficient in pollution removal, the final effluent of A2/O-MBR coupled with Electro-Fenton process could meet the standard of recycled water reuse or the first class A standard of municipal wastewater. This study revealed the mechanisms for anoxic biodegradation of NHCs, which are of great significant to enhance the refractory organics removal through the improvement of biochemical technology combination. |
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