Bioremediation Of Perchlorate And Mixed Contamination Of Perchlorate, Nitrate-nitrogen And Ammonia-nitrogen

Perchlorate contamination in the environment has been considered as a hotspot issuein the recent years. Included in this laboratory research were completely reducingperchlorate throμgh adding different electron donors, and introducing nitrogen as co-contaminant. The correlation between the change of perchlorate concentration andfunctional genes which encoded key enzyme during perchlorate reduction as pcrA andcld, denitrification process as NirS, or total bacteria as16SrRNA were assessed at thelevel of genes to further interpretation the mechanisms of perchloratebiodegradation.The main contents and results of this study were as follows:(1) The efficiency of degradation of10mg/L perchlorate in three systems withdifferent electron donors were shown as: the rate of perchlorate reduction with acetateas electron donor (AD)(completely degradation in100hours) was more rapid thanperchlorate reduction without any electron donor (ND)(completely degradation in240hours) and ND was faster than with hydrogen as electron donor (HD)(completelydegradation in71days).(2)Under the conditions of chemical indexes such as pH and DO which are suitablefor perchlorate bioremediation, the key factor that controlled the perchlorate reductionwas the expression of pcrA gene which encoded the α-subunit of perchlorate reductase.Pearson correlation index results showed that the expression of16SrRNA gene wasthe most apparently related to the change of ClO4-concentration in ND system(p=0.979); whereas cld to ClO4-in the AD system (p=0.157) and pcrA plus cld gene toClO4-in HD systems (p=0.732). It proved that ClO4-degradation under differentelectron donors were regulated by different microbial community in the reductionsystems, respectively.(3)When NO3-N was present as co-contaminant with ClO4-, under the condition thatadding sufficient acetate as electron donor, NO3-did not completely inhibit the ClO4-reduction in the concentration ratio of NO3-N to ClO4-were1and5. NO3-promotedClO4-reduction once the NO3-was completely removed.(4)Ammonium can be used as an extra nitrogen source for promoting the perchlorate reduction bacteria growth in the medium and accelerate the ClO4-bioremediation.When there existed only one kind of nitrogen contaminant in thesystem, ClO4-reduction did not be inhibited by the single nitrogen contaminant evenrisen the initial concentration of nitrogen. However, simultaneously existence of twokinds of nitrogen co-contaminants obviously improved the degradation efficiency ofClO4-.The correlation between the functional gene pcrA、cld and the concentrationof ClO4-were not so apparently, due to the limitations of using functional gene asmaker to represent specific microbial community in the mixed contamination systems.(5) The phylogenic analysis of the changes in microbial communities indicated thatthe typical perchlorate reduction bacteria such as Azospira and Dechloromonas wereprevalently existent in ND, HD and AD respectively. The composition and theabundance of specific microbial community played an important role in perchloratebioremediation, and can be used as a symbol of perchlorate reduction in environment.