Biological reduction of nitrate and perchlorate using autotrophic bacteria

Widespread contamination of ground and surface water with nitrate (NO3-) and perchlorate (ClO4 -) has been recorded in many US states. Nitrate and perchlorate are soluble anions that are known to affect human health. This dissertation presents the results of three studies of biological reduction ClO4 - and NO3- using autotrophic bacteria. In the first study, hydrogenotrophic (H2 oxidizing) denitrifiers were inoculated into two hollow fiber membrane bioreactors (HFMB), which were set up in different configurations (I and II). In Configuration I, H 2 passed through the lumen of the fibers and nitrified water flowed through the shell. In Configuration II, liquid flowed through the lumen and H2 through the shell. Complete denitrification was achieved in both systems with pH and biomass control at hydraulic retention times (HRT) of 8.3 and 1.5 hours for configurations I and II, respectively. Influent dissolved oxygen (DO) did not inhibit denitrification. The second study investigated reduction of NO3- and ClO4- in ion exchange (IX) brines using halophilic-hydrogenotrophic bacteria in a HFMB (Configuration II). Continuous operation of the HFMB resulted in partial denitrification (30%) of the brines. Batch HFMB operation resulted in average removal efficiencies of 30% and 42% for NO3- and ClO4-, respectively. The third study investigated ClO4- reduction using Sulfur Utilizing Perchlorate Reducing Bacteria (SUPeRB). SUPeRB cultures reduced 5-20 mg/L ClO4- to < 0.5 mg/L at varying salinities (0-30 g/L NaCl). Perchlorate (8-0.01 mg/L) reduction was achieved in packed bed reactors (PBR) inoculated with SUPeRB and filled with S° pellets and crushed oyster shells at empty bed contact times of 8-13 hours for low and high ClO4- concentrations, respectively. Decreased ClO4- removal efficiency was observed at increased recirculation velocity and with small S0 particle sizes. Influent DO or NO3- did not inhibit overall ClO4- removal.