[Effect of Sulfur to Quartz Sand Ratios on the Removal of High-Concentration Perchlorate in Packed-Bed Reactors]

Three autotrophic packed-bed reactors, each with a different sulfur/quartz sand ratio(R1, 2:1; R2, 1:1; R3, 1:2,)were used to remove high-concentration perchlorate from contaminated water. The perchlorate removal efficiency, kinetics, and biofilm of the reactors were studied using different perchlorate concentrations and hydraulic retention times (HRTs). The perchlorate removal efficiency decreased with higher perchlorate concentration and shorter HRT, and the removal efficiency of R1 was higher than of R2 and R3. The maximum removal loading of R1 was 2.18 kg·(m³·d)^-1at an HRT of 3.2 h and perchlorate concentration of 300 mg·L^-1. The half-order kinetics model fit the reactors' experimental data well; the reaction rate constants of R1, R2, and R3 were 8.036, 6.596, and 4.212 mg^1/2·(L^1/2·h)^-1. The yield of SO₄^2- was greater than the stoichiometric yield of sulfur autotrophic reduction owing to sulfur disproportionation. The disproportionation was inhibited with a higher perchlorate concentration or shorter HRT. Moreover, disproportionation of R3 was the weakest because the SO₄^2- yield of R3 was lower than of R1 and R2. The pH and alkalinity of the effluent increased with lower perchlorate concentration and shorter HRT. The development of biofilm in R2 and R3 was better than in R1. The secretion of extracellular polymeric substances can promote the formation of biofilm.