Studies on Microbial Reduction of Perchlorate in Batch and Continious Systems

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Perchlorate contamination of the ground water, soil and surface water is a public health concern of recent times due to their detrimental effect of human health and other living entities. Therefore, its removal from contaminated systems is necessary for the human well being and environment. Perchlorate salts (especially ammonium and sodium) are extensively used mostly in military ammunitions and fireworks industries all over the world. Several removal techniques such as ion exchange, adsorption and precipitation, chemical and electro-chemical processes have been tested for perchlorate from water systems. Those techniques majorly suffer from one or more disadvantages like, high maintenance cost, regeneration of brines and inefficient removal of perchlorate etc. In this scenario, the ecofriendly bioreduction using microbes in pure or mixed cultures shows promising future in the field of perchlorate removal from water and wastewater. The main focus of the present investigation was to develop a complete anaerobic treatment system for perchlorate bearing wastewater in anaerobic process using a mixed microbial consortium. The mixed microbial consortium was collected from an activated sludge reactor and investigated for its potential in perchlorate degradation from synthetic wastewater in batch shake flasks and as well as continuous systems. The capacity of the mixed microbial consortium to reduce perchlorate using phenol and other five different carbon sources and phenol was tested in batch system. Compared to other tested carbon-sources used in this study, succinate has proven to be better for perchlorate degradation by the mixed consortium predominantly Burkholderia sp. on the other hand the mixed microbial consortium predominantly Pseudoxanthomonas sp. was found to utilize phenol as sole C-source for perchlorate bioreduction which is reported for the first time. The mixed microbial culture grown in batch mode with perchlorate along with succinate and phenol separately was isolated to identify the predominant strains. The 16S rDNA analysis of the predominant strain showed to be Burkholderia. sp. using succiante as sole C-source in the mixed culture. For the first time Burkholderia. sp., predominantly present in this mixed culture, has been reported to be involved in perchlorate degradation. Newly isolated bacterial species Pseudoxanthomonas sp. isolated from a sewage sludge consortium was found to reduce perchlorate while taking phenol as electron acceptor. The optimum conditions for perchlorate reduction by the enriched mixed culture predominantly Burkholderia sp. was found to be 30oC and pH 7.0. Plackett and Taguchi design was employed for screening 5 parameters for perchlorate degradation from two isolated bacterial strains Burkholderia sp. and Pseudoxanthomonas sp., utilizing succinate and phenol as C-source. Four physical parameters: temperature, pH, inoculums age and inoculums volume were selected along with the ration of carbon source and perchlorate concentration. Coefficients and sum of squares ratio in percentage (%) of these variables were calculated by subjecting the experimental data to statistical analysis. Temperature, inoculum age and carbon to perchlorate ration showed significant importance in perchlorate degradation by mixed consortium predominantly with Burkholderia sp. using succinate as C .
Supervisors: Pranab Kumar Ghosh and Kannan Pakshirajan