[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 mg1/2·(L1/2·h)-1. The yield of SO42- 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 SO42- 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.

[Removal Characteristics of High Concentrations of Perchlorate Using a "Heterotrophic Sulfur Autotrophic" Combination Process].

The heterotrophic-autotrophic reactor including two chambers, that is, the lower part of the heterotrophic zone and the upper part of the autotrophic zone, was used to remove highly concentrated perchlorate (ClO4-) wastewater. The reduction characteristics of ClO4- and the effluent sulfur (SO42-) concentration were investigated using different influent ClO4- concentrations and C/Cl ratios. By adjusting the influent C/Cl ratio from 2 to 1, the reactor was started up successfully within 36 d. The microorganisms tolerated the high concentration of ClO4- (250-400 mg·L-1) and the ClO4- removal efficiency was higher than 95%. By adjusting the C/Cl ratio to 1.2, the ClO4- load in the autotrophic zone was reduced and the SO42- concentration in the effluent was controlled below 250 mg·L-1. The result show that tryptophan and tyrosine materials in soluble microbial products led to the TOC increase in the effluent of the autotrophic zone. The sludge yield was reduced because of heterotrophic and autotrophic processes. The alkalinity produced by the heterotrophic process was used as carbon source for the autotrophic process and to neutralize the acidity produced by the autotrophic process, representing the complementary function and avoiding the addition of alkalinity in the autotrophic process.

[Characteristics of Perchlorate Reduction and Analysis of Consortium Structure in a Sulfur-Based Reactor at a High Perchlorate Concentration].

The effects of perchlorate concentration and hydraulic retention time (HRT) on perchlorate reduction characteristics were investigated in a sulfur-based perchlorate reduction reactor.The results showed that the perchlorate was completely removed at HRT of 12 h and the influent perchlorate concentration ranged from 50 mg·L-1 to 194 mg·L-1;The perchlorate removal efficiency was 74% at HRT of 4 h and the influent perchlorate concentration was 194 mg·L-1;The yield of sulfate was increased by increasing the influent perchlorate concentration and HRT;The influent pH and alkalinity was approximately 8.0 and 500 mg·L-1 CaCO3,and the effluent pH and alkalinity was approximately 6.7 and 100 mg·L-1 CaCO3,respectively;The oxidation reduction potential (ORP) ranged from -380 mV to -330 mV at the bottom of the reactor,however,ORP ranged from -300 mV to -250 mV at the top of the reactor;The molecular biological analysis showed that the microbial consortium structure was different along the flow path in the reactor,Sulfurovum which is known to oxidize sulfur was decreased from 57.78% to 32.19% and Hydrogenophilaceae which is known to oxidize hydrogen sulfide was increased from 4.35% to 22.24%.