Impact of Fe(Ⅱ)addition timing on the removal of different forms of As or Sb by sulfate reducing bacteria
In sulfate-reducing bacteria(SRB)matrices,50 mg/L Fe(Ⅱ)and various forms of As or Sb(with initial mass concentrations of 5 mg/L)were added at different time intervals to design four treatments:T1,simultaneous addition of As(Ⅴ),Sb(Ⅴ),and Fe(Ⅱ);T2,addition of Fe(Ⅱ)two days in advance followed by As(Ⅴ)and Sb(Ⅴ);T3,simultaneous addition of As(Ⅲ),Sb(Ⅲ)and Fe(Ⅱ);T4,addition of Fe(Ⅱ)two days in advance followed by As(Ⅲ)and Sb(Ⅲ).The changes in matrix pH,redox potential,optical density(OD600),total alkalinity,SO42-,sulfide,Fe,As and Sb content over time were analyzed to clarify the impact of Fe(Ⅱ)on the efficiency and mechanism of As and Sb removal.The results showed that in matrices with sufficient sulfide(sulfide residual＞8 mg/L),the removal rate of Sb in all treatments could reach over 98％after 7 days,while the removal rate of As ranged from 38.42％to 87.36％.Re-dissolution of As and Sb occurred in the later stages of the experiment,and Sb was generally easier to be solidified than As.The prior addition of Fe(Ⅱ)was conducive to the removal of As and Sb,but the form of As and Sb had a more significant impact on the removal effect than the timing of Fe(Ⅱ)addition.As(Ⅲ)and Sb(Ⅲ)exhibited faster removal rates and higher removal rates than As(Ⅴ)and Sb(Ⅴ).After 14 days of treatment,the residual Sb in T3 and T4 was below the detection limit,while the residual As was 1.94 and 0.62 mg/L,respectively.Therefore,when treating As and Sb containing wastewater through sulfur reduction,in addition to improving the removal rate by adding an appropriate amount of Fe(Ⅱ),appropriate measures should also be taken to promote the reduction of As and Sb to achieve more significant stabilization effects.
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