Distribution of Nitrifying Bacteria Under Fluctuating Environmental Conditions.

摘要

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 flood-and-drain 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 NO3 -. At a flooding frequency of 8-cycles per day, NO 3 - 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 nosZ gene as a presence-absence indicator. Vertical profiles of creek sediments showed a relationship between denitrifier abundance and organic matter 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.