Microbial Communities in Partially and Fully Treated Effluent of Three Nitrogen-Removing Biofilters

Abstract

In the United States, 24% of single-family homes have on-site wastewater treatment systems (OWTS). Not only is the proportion much higher in some areas, but also most of the OWTS provide no nitrogen removal. An innovative alternative to such OWTS are nitrogen-removing biofilters (NRBs), passive two-layer systems designed to select nitrifying (top layer) and denitrifying (bottom layer) microbial assemblages from incoming microorganisms to remove nitrogen from household wastewater by sequential nitrification-denitrification. Little is known about the microbial ecology of NRBs, or even about best practices for investigating NRB microbiology. This study characterized microbial communities of wastewater passing through three NRBs that differed in construction and nitrogen-removal efficiency by sampling nondestructively at four times over 1 year. Microbial assemblages collected from pan lysimeters buried within NRBs and from final effluent were distinct from the influent community, indicating environmental conditions in NRBs were selecting specific microbial communities. Principal coordinate analysis (weighted UniFrac) showed extensive overlap of microbial communities from different systems, layers, and times, as well as significant relationships between microbial community structure and NRB function (nitrogen transformation and removal). Genus-level analysis revealed differences between systems in dominant nitrifiers and that denitrification is likely driven by different bacteria than typically dominate in wastewater treatment plants. Replicated experiments and alternative sampling approaches will be necessary to elucidate whether differences in microbial communities between systems reflected environmental selection due to differences in NRB design, and how much stochastic processes affect NRB microbial community structure.