Distribution of Nitrifying Bacteria Under Fluctuating Environmental Conditions

Engineered systems that mimic tidal wetlands are ideal for point - of - source treatment of wastewater due to their low energy requirements and small physical footprint. In this study, vertical columns were constructed to mimic the - cycles of tidal wetland treatment systems (TWTS) in order to study how variations in the frequency and duration of flooding affect the efficiency of microbially - mediated nitrogen removal from synthetic wastewater (containing whey protein and NH4+). Altering the frequency of flooding, which determines the temporal juxtaposition of aerobic and anaerobic conditions in the reactor, had a significant effect on overall nitrogen removal; columns more frequent cycling were very efficient at converting the NH4+ in the feed to N03". At a flooding frequency of 8 - cycles per day, N03" began to disappear from the systems in both High -and Low - N treatments. The longer flooding duration appeared to increased anaerobiosis and allowed denitrification to proceed more effectively, while allowing nitrification to proceed when oxygen was available. Analysis of depth profiles of abundance revealed distinct differences between the tidal and trickling systems abundance profiles. Overall, these results demonstrate a tight coupling of environmental conditions with the abundance of ammonium oxidizing bacteria and suggest several experimental modifications, such variable tidal cycles, could be implemented to enhance the functioning of TWTS. Field work conducted at Cobb Mill Creek showed similar distribution patterns in denitrifying bacteria. Denitrifiers were enumerated using an MPN - PCR approach utilizing the n0sZ gene as a presence - absence indicator. Vertical profiles of creek sediments showed a relationship between denitrifier abundance and organic matter iii content. Like the treatment columns, there was a zone where abundance showed a significant increase. Increases in abundance represent a Golidlocks zone, a region where conditions are optimized for microbial growth and metabolism. Potential denitrification rates confirmed increased metabolic activity concurrent with increases in denitrifier abundance. Both TWTS and sediment profiles offer a unique look at the distribution of microorganisms often treated as a black box, summarized as a reaction rate constant by engineers or modelers.

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