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Shallow narrow drainfields are assumed to provide better wastewater renovation than conventional drainfields and are used for protection of surface and ground water. To test this assumption, we evaluated the water quality functions of two advanced onsite wastewater treatment system (OWTS) drainfields-shallow narrow (SND) and Geomat (GEO)-and a conventional pipe and stone (P&S) drainfield over 12 mo using replicated ( = 3) intact soil mesocosms. The SND and GEO mesocosms received effluent from a single-pass sand filter, whereas the P&S received septic tank effluent. Between 97.1 and 100% of 5-d biochemical oxygen demand (BOD), fecal coliform bacteria, and total phosphorus (P) were removed in all drainfield types. Total nitrogen (N) removal averaged 12.0% for P&S, 4.8% for SND, and 5.4% for GEO. A mass balance analysis accounted for 95.1% (SND), 94.1% (GEO), and 87.6% (P&S) of N inputs. When the whole treatment train (excluding the septic tank) is considered, advanced systems, including sand filter pretreatment and SND or GEO soil-based treatment, removed 99.8 to 99.9% of BOD, 100% of fecal coliform bacteria and P, and 26.0 to 27.0% of N. In contrast, the conventional system removed 99.4% of BOD and 100% of fecal coliform bacteria and P but only 12.0% of N. All drainfield types performed similarly for most water quality functions despite differences in placement within the soil profile. However, inclusion of the pretreatment step in advanced system treatment trains results in better N removal than in conventional treatment systems despite higher drainfield N removal rates in the latter.

Climate change may affect the ability of soil-based onsite wastewater treatment systems (OWTS) to treat wastewater in coastal regions of the Northeastern United States. Higher temperatures and water tables can affect treatment by reducing the volume of unsaturated soil and oxygen available for treatment, which may result in greater transport of pathogens, nutrients, and biochemical oxygen demand (BOD5) to groundwater, jeopardizing public and aquatic ecosystem health. The soil treatment area (STA) of an OWTS removes contaminants as wastewater percolates through the soil. Conventional STAs receive wastewater from the septic tank, with infiltration occurring deeper in the soil profile. In contrast, shallow narrow STAs receive pre-treated wastewater that infiltrates higher in the soil profile, which may make them more resilient to climate change. We used intact soil mesocosms to quantify the water quality functions of a conventional and two types of shallow narrow STAs under present climate (PC; 20°C) and climate change (CC; 25°C, 30 cm elevation in water table). Significantly greater removal of BOD5 was observed under CC for all STA types. Phosphorus removal decreased significantly from 75% (PC) to 66% (CC) in the conventional STA, and from 100% to 71–72% in shallow narrow STAs. No fecal coliform bacteria (FCB) were released under PC, whereas up to 17 and 20 CFU 100 mL-1 were released in conventional and shallow narrow STAs, respectively, under CC. Total N removal increased from 14% (PC) to 19% (CC) in the conventional STA, but decreased in shallow narrow STAs, from 6–7% to less than 3.0%. Differences in removal of FCB and total N were not significant. Leaching of N in excess of inputs was also observed in shallow narrow STAs under CC. Our results indicate that climate change can affect contaminant removal from wastewater, with effects dependent on the contaminant and STA type.

Advanced N‐removal onsite wastewater treatment systems (OWTS) rely on nitrification and denitrification to remove N from wastewater. Despite their use to reduce N contamination, we know little about microbial communities controlling N removal in these systems. We used quantitative polymerase chain reaction and high‐throughput sequencing targeting nitrous oxide reductase (nosZ) and bacterial ammonia monooxygenase (amoA) to determine the size, structure, and composition of communities containing these genes. We analyzed water samples from three advanced N‐removal technologies in 38 systems in five towns in Rhode Island in August 2016, and in nine systems from one town in June, August, and October 2016. Abundance of nosZ ranged from 9.1 × 103 to 9 × 108 copies L−1 and differed among technologies and over time, whereas bacterial amoA abundance ranged from 0 to 1.9 × 107 copies L−1 and was not different among technologies or over time. Richness and diversity of nosZ—but not amoA—differed over time, with median Shannon diversity indices ranging from 2.61 in October to 4.53 in August. We observed weak community similarity patterns driven by geography and technology in nosZ. The most abundant nosZ‐ and amoA‐containing bacteria were associated with water distribution and municipal wastewater treatment plants, such as Nitrosomonas and Thauera species. Our results show that nosZ communities in N‐removal OWTS technologies differ slightly in terms of size and diversity as a function of time, but not geography, whereas amoA communities are similar across time, technology, and geography. Furthermore, community composition appears to be stable across technologies, geography, and time for amoA. Core Ideas We describe N‐cycling bacterial communities in advanced N‐removal septic systems. Geographic factors are weak drivers of community composition in nosZ. Technology design is a weak driver of community composition in nosZ. Community composition of amoA is similar across time, space, and among technologies Time drives differences in nosZ—but not amoA—diversity and abundance.

Biological nitrogen removal (BNR) systems are increasingly used in the United States in both centralized wastewater treatment plants (WWTPs) and decentralized advanced onsite wastewater treatment systems (OWTS) to reduce N discharged in wastewater effluent. However, the potential for BNR systems to be sources of nitrous oxide (N 2 O), a potent greenhouse gas, needs to be evaluated to assess their environmental impact. We quantified and compared N 2 O emissions from BNR systems at a WWTP (Field's Point, Providence, RI) and three types of advanced OWTS (Orenco Advantex AX 20, SeptiTech Series D, and Bio-Microbics MicroFAST) in nine Rhode Island residences (n = 3 per type) using cavity ring-down spectroscopy. We also used quantitative polymerase chain reaction to determine the abundance of genes from nitrifying (amoA) and denitrifying (nosZ) microorganisms that may be producing N 2 O in these systems. Nitrous oxide fluxes ranged from −4 ´ 10 −3 to 3 ´ 10 −1 mmol N 2 O m −2 s −1 and in general followed the order: centralized WWTP > Advantex > SeptiTech > FAST. In contrast, when N 2 O emissions were normalized by population served and area of treatment tanks, all systems had overlapping ranges. In general, the emissions of N 2 O accounted for a small fraction (<1%) of N removed. There was no significant relationship between the abundance of nosZ or amoA genes and N 2 O emissions. This preliminary analysis highlights the need to evaluate N 2 O emissions from wastewater systems as a wider range of technologies are adopted. A better understanding of the mechanisms of N 2 O emissions will also allow us to better manage systems to minimize emissions. Comparison of N 2 O Emissions and Gene Abundances between Wastewater Nitrogen Removal SystemsElizabeth Quinn Brannon,* Serena M. Moseman-Valtierra, Brittany V. Lancellotti, Sara K. Wigginton, Jose A. Amador, James C. McCaughey, and George W. Loomis H umans substantially modify global nitrogen (N) cycles by industrially fixing N for fertilizer and ultimately releasing reactive N back to the environment through various mechanisms, including wastewater treatment. The continued growth of the human population will lead to further increases in excess reactive N, increasing the need for N remediation (Galloway et al., 2003). In recent years, remediation has focused on upgrading centralized wastewater treatment plants (WWTPs) to include biological nitrogen removal (BNR). Since one in five US homes are serviced by conventional onsite wastewater treatment systems (OWTS) (USEPA, 2013) they can also be large sources of N (Zhu et al., 2008;USEPA, 2015). The use of OWTS can be advantageous relative to centralized WWTPs, as they recharge groundwater supplies, require less infrastructure, and have lower energy costs (USEPA, 2013). To ameliorate N inputs to the environment, conventional OWTS are also being upgraded to advanced OWTS that include BNR.Although BNR systems at WWTPs and OWTS vary in design, all employ nitrifying (conversion of ammonium to nitrate) and denitrifying (convers...