Ecological Interactions Among Nitrate-, Perchlorate-, and Sulfate-Reducing Bacteria in Hydrogen-Fed Biofilm Reactors

Water contamination with nitrate (NO3-) (from fertilizers) and perchlorate (ClO4-) (from rocket fuel and explosives) is a widespread environmental problem. I employed the Membrane Biofilm Reactor (MBfR), a novel bioremediation technology, to treat NO3- and ClO4- in the presence of naturally occurring sulfate (SO4 2-). In the MBfR, bacteria reduce oxidized pollutants that act as electron acceptors, and they grow as a biofilm on the outer surface of gas-transfer membranes that deliver the electron donor (hydrogen gas, (H 2). The overarching objective of my research was to achieve a comprehensive understanding of ecological interactions among key microbial members in the MBfR when treating polluted water with NO3- and ClO4- in the presence of SO4 2-. First, I characterized competition and co-existence between denitrifying bacteria (DB) and sulfate-reducing bacteria (SRB) when the loading of either the electron donor or electron acceptor was varied. Then, I assessed the microbial community structure of biofilms mostly populated by DB and SRB, linking structure with function based on the electron-donor bioavailability and electron-acceptor loading. Next, I introduced ClO4- as a second oxidized contaminant and discovered that SRB harm the performance of perchlorate-reducing bacteria (PRB) when the aim is complete ClO4- destruction from a highly contaminated groundwater. SRB competed too successfully for H2 and space in the biofilm, forcing the PRB to unfavorable zones in the biofilm. To better control SRB, I tested a two-stage MBfR for total ClO4 - removal from a groundwater highly contaminated with ClO 4-. I document successful remediation of ClO 4- after controlling SO4 2- reduction by restricting electron-donor availability and increasing the acceptor loading to the second stage reactor. Finally, I evaluated the performance of a two-stage pilot MBfR treating water polluted with NO 3- and ClO4-, and I provided a holistic understanding of the microbial community structure and diversity. In summary, the microbial community structure in the MBfR contributes to and can be used to explain/predict successful or failed water bioremediation. Based on this understanding, I developed means to manage the microbial community to achieve desired water-decontamination results. This research shows the benefits of looking "inside the box" for "improving the box".