Study On Kinetics Of Biological Perchlorate Reduction With Sulfur Autotrophic

As a kind of inorganic contaminant, perchlorate is toxic, highly stabile andrapidly diffused. Perchlorate can interefer with function of the thyroid in the humanbody, which affect the metabolism of the human body. Because of high removalefficiency and low cost, biological degradation has been more applied to degradatethe perchlorate in the water.In this research, enrichment and cultivation of sulfur autotrophic reducingbacteria are investigated by using aerobic sludge and anaerobic sludge from sewageplant as seeding sludge, resepectively, including sulfur autotrophic perchloratereducing bacteria, mixed bacteria of sulfur autotrophic perchlorate reducing bacteriaand denitrifying bacteria, and sulfur autotrophic denitrifying bacteria. The degradationand microbial community structure are analyzed in the enrichment and cultivation,and then kinetics of perchlorate reduction process is researched. Parmaeters aeffectingperehlorate reduction rate are researched using sulfur autotrophic perchlorate reducingbacteria. The experimental results are as follows:Both aerobic sludge and anaerobic sludge from sewage plant as seeding sludgecan be successfully acclimated to be sulfur autotrophic perchlorate reducing bacteria,mixed bacteria of sulfur autotrophic perchlorate reducing bacteria and denitrifyingbacteria, and sulfur autotrophic denitrifying bacteria. In the enrichment andcultivation, Cl_O^4-can completely transform to Cl^-. Due to the disproportionatereaction of S⁰in the reduction of the Cl_O^4-, the actual production of SO₄^2-is greaterthan its theory production. In the reduction of Cl_O^4-, the production of H⁺can causethe pH value of solution decreased, as well as the process of denitrifying bacteriareducing the NO₃^-, but the pH value in the solution remains in the range of6.5to7.2,which is suitable for the growth and metabolism of the reducing bacteria.In the enrichment and cultivation process of sulfur autotrophic perchloratereducing bacteria, mixed bacteria of sulfur autotrophic perchlorate reducing bacteria and denitrifying bacteria, sulfur autotrophic denitrifying bacteria, rod bacterium isgradually increased, which become the superior strain at last. The microbialcommunity structures in different stages are studied by PCR-DGGE and clonetechnique. Microbial community structures in the sludge are changing in differentcultivation periods, and the DGGE bands show that proteobacteria is the superiorstrain in both perchlorate reduction bacteria and denitrifying bacteria.Batch experiments are conducted to investigate the kinetics of perchloratereduction by sulfur autotrophic perchlorate reducing bacteria, mixed bacteria of sulfurautotrophic perchlorate reducing bacteria and denitrifying bacteria, sulfur autotrophicdenitrifying bacteria, respectively. The maximum specific substrate removal rate, q_max,are0.142mgCl_O^4-/mgDW-day and0.114mgCl_O^4-/mgDW-day, in the batchexperiment using sulfur autotrophic perchlorate reducing bacteria by aerobic sludgeand anaerobic sludge as seeding sludge, respectively, from which can see the sulfurautotrophic perchlorate reducing bacteria acclimated from aerobic sludge has similardegradation rate with perchlorate reducing bacteria acclimated from anaerobic sludge.The Ks and Y_xmaxare5.706and0.1896mgDW/mgCl_O^4-, respectively, in the batchexperiment using sulfur autotrophic perchlorate reducing bacteria acclimated fromaerobic sludge. The Ks and Y_xmaxare29.47and0.2199mgDW/mgCl_O^4-, respectively,in the batch experiment using sulfur autotrophic perchlorate reducing bacteriaacclimated from anaerobic sludge. The mixed bacteria of sulfur autotrophicperchlorate reducing bacteria and denitrifying bacteria has worse degradation rate ofpercholrate than sulfur autotrophic perchlorate reducing bacteria. At the beginning,the denitrifying bacterium almost has no degradation effect on perchlorate, but afterabout ten days, it has a rapid degradation rate in the reduction of perchlorate.Sulfur autotrophic perchlorate reducing bacteria acclimated from aerobic sludgehas a maximum rate at pH7.0. Lower or higher pH value can affect the perchloratereduction rate. The nitrate inhibits perchlorate reduction by obtaining electron prior toperchlorate, which result to that nitrate is degraded firstly. And the perchloratereduction rate is very slowly in the process of nitrate degradation, when the nitrate istotally degraded, the perchlorate starts to be degraded quickly. Comparing S₂O₃^2-as electron donor with S⁰as electron donor, the sulfur autotrophic perchlorate reducingbacteria acclimated from aerobic sludge has a similar reduction rate. However, whenusing Fe⁰、H₂、CH₃COO-as electron donor, sulfur autotrophic perchlorate reducingbacteria has a poor degradation effect on perchlorate. Therefore, the sulfur autotrophicperchlorate reducing bacteria with S⁰as electron donor can preferably come to a gooddegradation rate on perchlorate under condition of S₂O₃^2-as electron donor.