Removal Of Typical Brominated Organic Contaminants By Transition Metal Ions-activated Sulfite Systems

Brominated organic pollutants（BOCs）posed increasing threats to the environment and human health because of their cumulative toxic effect.Tetrabromobisphenol A（TBBPA）and 1,3,6,8-tetrabromocarbazole（1,3,6,8-BCZ）are two typical BOCs,which could not be removed by conventional water treatment processes.Advanced oxidation processes（AOPs）have a good removal efficiency on these two contaminants but most of them are high cost and may cause secondary pollution.The transition metal activated sulfite oxidation process has a good prospect in the treatment of organic wastewater because it is widely applicable,environmentally friendly,cheap cost,etc.Fe（Ⅲ）,Fe（Ⅱ）,Cr（Ⅵ）,Cu（Ⅱ）,Co（Ⅱ）and Mn（Ⅱ）were selected as typical transition metal ions to activate sulfite for removing TBBPA and 1,3,6,8-BCZ,and the mechanism for the removal of TBBPA and 1,3,6,8-BCZ were also evaluated.The main conclusion are as follows:Fe（Ⅲ）and Fe（Ⅱ）could effectively activate sulfite to remove BOCs.When the iron ions dose was 80μM and the sulfite dose was 0.2 m M,the removal rates of TBBPA and1,3,6,8-BCZ were 42.9%and 65.7%,respectively,in Fe（Ⅲ）/sulfite system at pH 4.0.In Fe（Ⅱ）/sulfite system,under the same condition,the removal rates were52.1%（TBBPA）and 53.9%（1,3,6,8-BCZ）.As for the other systems including Cr（Ⅵ）/sulfite,Cu（Ⅱ）/sulfite,Co（Ⅱ）/sulfite and Mn（Ⅱ）/sulfite,only Cr（Ⅵ）/sulfite system was capable in removing TBBPA（47.7%）,whereas these selected systems could not be used in removing 1,3,6,8-BCZ.For TBBPA,the removal rate firstly increased with the elevation of iron ions concentration from 10 to 20μM and then decreased with further elevating theseions to100μM in the iron ions/sulfite systems（i.e.,Fe（Ⅲ）/sulfite and Fe（Ⅱ）/sulfite）.In comparision,the increased concentration of Cr（Ⅵ）did not retard the removal of TBBPA in the Cr（Ⅵ）/sulfite system.Elevating the dosage of sulfite from 50 to 800μM could accelerate the reaction rate.High removal effect of TBBPA were always achieved between pH 3.0 to 7.0,but the removal effect of TBBPA decreased with the increase of the initial pH value.The presence of HA significantly retarded the removal of TBBPA,while the presence of HCO₃^-did not show significantly retard at pH 4.0.As for 1,3,6,8-BCZ,the increasing iron ions concentration could accelerate the removal rate in the iron ions/sulfite systems,while the increasd dosage of sulfite cannot enhance the1,3,6,8-BCZ removal.1,3,6,8-BCZ could not be removed at pH 3.0,and this removal rate increased when initial pH raised from 4.0 to 7.0.HA significantly inhibited the removal of 1,3,6,8-BCZ in the iron ions/sulfite systems,while HCO₃^-played no role in this process.TBBPA was mainly removed by HO^·and SO₄^·-degrading.The LC-MS was applied to measure the degradation products of TBBPA,most of which were macromolecular phenols.Combining the calculation of density functional theory and the identified products of TBBPA,the degradation pathway of TBBPA was proposed,where the initial reaction is debromination or bromine atoms replaced by hydroxyl groups.1,3,6,8-BCZ was removed in this system via flocculation and adsorption processes,and some1,3,6,8-BCZ was still oxidized by free radicals.The degradation pathway inferred by the density functional theory was in line with the actual product measured by GC-MS,which includes the breaking of the C-N bond in the molecule and the debromination or substitution reaction of the carbon atom on the benzene ring.This study found that the removal of TBBPA and 1,3,6,8-BCZ were inhibited in real water,but there was still a certain removal of these two pollutants.Comparing with other systems,the iron ions/sulfite systems were more effectively,cheap cost and environmentally friendly.