| The discharge value and cost of treatment of paper effluents are high.What's more,the content of toxic organic pollutants in wastewater is still high after conventional secondary treatment and it's hard to degrade the organics.This problem has seriously affected the sustainable development of environment and human beings.Recent years,the research about the fast ionic conductor draws more and more attention.The low-cost nature minerals bentonite has good adsorptivity and conductivity and is a kind of abundant fast ionic conductor.However bentonite may not remove the organic pollutants efficiently.The nanoscale zero valent iron?nZVI?with strong reducibility and high conductivity could degrade the organics more effectively.Unfortunately the weakness of aggregate may decrease its reactivity.So in this study,firstly,we prepared inorganic sodium bentonite?Na-bent?,nanoscale zero valent iron?nZVI?and bentonite based?intercalated or loaded?nanoscale zero valent iron?B-n ZVI?,which are low-cost fast ionic conductors.Then the X-ray diffraction analysis?XRD?and scanning electron microscope?SEM?was detected to characterize these interlayer structure and surface microstructure.What's more,their conductivity was tested.The results found that,for B-n ZVI,its interlamellar spacing increased,which illustrated a part of Fe0 had inserted into the layer of bentonite.The other hand,Fe0 distributed more uniform on the surface of benonite,and this could decrease the chance to be oxidized.In these three fast ionic conductors,the conductivity of B-nZVI was the most perfect.Next we used these conductors to adsorb and degrade wastewater in same conditions.Finally from the characterization and the results of wastewater treatment could conclude that the property of B-n ZVI fast ionic conductor was more excellent.The B-nZVI conductor could be regarded as granule electrodes and combine with graphite and aluminum to form three-dimensional electrode system respectively.Then we treated the secondary outlet wastewater of pulp and paper mills advanced.The effects of electrolysis time,cell voltage,plates distance,the dosage of granulated electrodes and initial pH of wastewater on the removal efficiency of CODCr,color and concentration of lignin were worked out.In graphite + B-nZVI three dimensional electrode system the optimum electrolysis time = 50 min,cell voltage = 30 V,plates distance = 4 cm,initial pH = 3 and the dosage of granules = 0.2 g.At the optimum experimental conditions,the removal rate of CODCr,color and concentration of lignin was 86.5%(decrease to be 40 mg·L-1),83.3% and 95.7% separately.In Al + B-n ZVI three dimensional electrode system,the optimum electrolysis time = 40 min,cell voltage = 25 V,plates distance = 4 cm,initial pH = 5 and the dosage of granules = 0.2 g.At the optimum conditions,the removal rate of CODCr,color and concentration of lignin was 91.1%,93.3% and 96.4% separately.Finally the CODCr could decrease to be 24 mg·L-1 and reached the discharge standards.Furthermore,the repeated performance of B-n ZVI in two systems was different because of the various operating mechanism of plates.To further prove the application of fast ionic conductor was feasible and effective in advanced degrading pulp and paper wastewater,we detected and analyzed the change of contents and types of organic pollutants by GC-MS and qualitatively calculated their removal rate by area normalization and integral method.The results were practicable and suitable.Finally,the different mechanisms of wastewater treatment in various three-dimensional electrode systems were expatiated: the conductivity of graphite was better,but it only could electrolyze and oxidize the wastewater and the gas production at the cathode was so less that not enough H2O2 generated.As for the Al plate,in addition to the electrolytic oxidation,the impact of electrocoagulation and electrofloatation was also important.In these two systems,the effect of electro-Fenton might be the most critical reaction mechanism. |
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