The Treatmentof Azo Dye-containing Effluentby Zero-Valent Aluminum Reduction Combinedwith Advanced Oxidation Process

Syntheticazodye is extensively used in commercial applicationsand there is huge amount of azo dye containing effluent inevitably.Color is the first contaminant to be visible in dyes-containing wastewater,in addition,most of these dye compounds are toxic and poses a serious hazard to aquatic living organisms inhabitant around.The degradation of model synthetic azo dye treating with zero-valent aluminum（ZVAL）under alkali conditions couple with Fenton and irradiation oxidationmethod was investigated inthe paper.In order to acquiresatisfieddecolorization,the dye-containing effluent was treatedthrough ZVAL reduction under alkaline conditions.The effects of the major operating parameters,such as solution pH,aluminum dosageand temperature were systematically evaluated.Assolution pHincrease from 7 to 12,decolorizationefficiency elevate from 62.6% to 98.4%and when effluent temperature increase from 30 to 80oC,decolorizationefficiencyimprove from 87.6% to 98.6%,Atthe same time,decolorizationefficiencyincrease from 89.6% to 98.7% when aluminum dosage from 5 g/L to 50 g/L.Toexplore whether ZVAL reduction treatmentis effective to all azodye-containing effluent,the reduction degeneration mechanism is invested.FTIR and ESI-MS characterization revealed that the azo bonds were broken down and reduced to aromatic anilines.Combinewith influence of particle scavenger methanol and carbon tetrachloride,the degeneration mechanism was deduced that the ZVAL react with H+ in water and generate nascent hydrogen,which attack and cleave the chromopHore –N=N-bond and form aromatic anilines.The cleavage of –N=N-lead to the decolorization of azo dye-containing effluent.While satisfied decolorization was acquired with the reduction of ZVAL,the organic content TOC cannot reduce through the cleavage of azo dye.To further degrade the azodye-containing effluent,Fenton reaction isinvested.The influence of hydrogen peroxide concentration,ferrous ion concentrationand solution pHwasstudiedsystematically.The result turns out that asthe hydrogen peroxide dosage from 10 mM to 50 mM,the TOC degradationefficiency increase from 73.8% to 93.3% and as the ferrous ion concentration increase from 0.025 mM to 1 mM,the TOC degradationefficiency increase from 55.6% to 91.6%.TheTOC degradationefficiencyis the highestat solution pHis 2 and 3 when other condition is the same.The treatment of azodye-containing effluent using ZVAL couple with Fenton oxidation is much more effective comparing with treating with Fenton oxidation.Thefollowing three aspects :1)After treating with ZVAL,the aromatic anilineis more vulnerable to oxide;2)the remainingaluminum can reduce ferric ion to ferrous ion;3)the flocculationof aluminum ioncan attribute to the enhancementof TOC degradationefficiency.Further investment revealsthateach aspect can enhance the TOC degradationefficiencyby 25%,25% and 4% respectively.Azodye-containing effluent treating with ZVAL reduction combine with irradiationwasalsostudied.“BaF₂-TiO₂”composite wassynthesizedthrough loading BaF₂ and TiO₂on aerogels,and the crystalline formof TiO₂ is anatase,which is of highcatalytic activities.The performance is much better when treating with ZVAL reduction combine with irradiationthan irradiationalone.The solution pH,initial azodyeconcentration and the dosage of “BaF₂-TiO₂”composite was studied.The result shows that TOC degradationefficiencyincrease first and then decreaseas the pHincreasedwhile sharp declinewhen initial azodyeconcentration from 50 ppmto 500 ppm.TOC degradationefficiencyenhance asthedosage of “BaF₂-TiO₂”composite increaseand the performance is the best when BaF₂:TiO₂=1.