Abstract
Wastewater is a major source of nitrogen (N) to groundwater and coastal waterbodies, threatening both environmental and public health. Advanced N-removal onsite wastewater treatment systems (OWTS) are used to reduce effluent N concentration through biological N removal (BNR). Despite the important role that these systems play in treating nutrient- and pathogen-rich wastewater, few studies have targeted the mechanisms involved in N removal, their capacity to produce effluent to meet regulatory standards, or their impact on the atmosphere. I evaluated effluent total N (TN) concentration, the structure and composition of N-removing microbial communities, and greenhouse gas fluxes of advanced N-removal OWTS in the town of Charlestown, Rhode Island, USA. To assess N outputs from advanced OWTS and compliance with the 19 mg N/L state regulatory standard for advanced-treated effluent, in Manuscript 1 I quantified TN concentration of effluent from 50 advanced N-removal OWTS between March 2017 and December 2019, and evaluated differences as a function of N-removal technology, home occupancy pattern (systems used seasonally vs. those used year-round), and various wastewater properties. Four N-removal OWTS technologies were included in this study: (i) Orenco Advantex® AX20 (n = 33), (ii) Orenco Advantex® RX30 (n = 9), (iii) BioMicrobics MicroFAST® (n = 3), and Norweco Singulair® (models TNT, 960, and DN; n = 5). RX30 systems produced the lowest median TN concentration (mg N/L) (13.2), followed by FAST (13.4), AX20 (14.9) and Norweco (33.8). Compliance with the state standard varied among technologies, with compliance rates of 78%, 73%, 67%, and 0% for RX30, AX20, FAST, and Norweco systems, respectively. Effluent TN concentration did not vary as a function of occupancy pattern. Ammonium and nitrate were identified as predictors for effluent TN in all technologies; temperature and pH were also part of best-fit models for FAST and Norweco systems, respectively. Systems used year-round produced a significantly higher median daily (5.3 g N/d) and annual (2.3 kg N/yr) N load than did seasonally-used systems (3.7 g N/d and 0.41 kg N/yr), likely due to differences in home usage patterns, demographics, and associated differences in system flow. Assessment of treatment capabilities of advanced N-removal OWTS requires fast, accurate methods of monitoring performance. Regular monitoring of OWTS using in situ rapid tests can provide an inexpensive option for assessing treatment performance. In Manuscript 2 I assessed the ability of a portable photometer to accurately measure ammonium and nitrate concentrations in final effluent from 46 advanced N-removal OWTS
Highlights
Effluent from onsite wastewater treatment systems (OWTS) is an important source of nitrogen to coastal watersheds (Valiela et al, 2010)
Values for AX20 and FAST systems are comparable to those reported by Lancellotti et al (2017), who evaluated the effectiveness of 42 advanced N-removal OWTS in six Rhode Island towns within the Greater Narragansett Bay watershed between March 2015 and August 2016
RX30 systems produced effluent with the lowest median total N (TN) concentration (13.2), followed by FAST (13.4), AX20 (14.9), and Norweco systems (33.8)
Summary
Effluent from onsite wastewater treatment systems (OWTS) is an important source of nitrogen to coastal watersheds (Valiela et al, 2010). Advanced N-removal OWTS aim to reduce N levels in wastewater by cycling it through an advanced treatment train that promotes successive nitrification (the conversion of ammonium to nitrate) and denitrification (the conversion of nitrate to nitrous oxide and/or dinitrogen gas), resulting in N being removed from the wastewater and emitted into the atmosphere (Fig. 2.1; Oakley et al 2010). Advanced onsite wastewater treatment systems (OWTS) – designed to remove N from wastewater – are often required in areas vulnerable to excess N inputs (Amador et al, 2018) These technologies vary in their design, but they all have an oxic zone to facilitate nitrification and an anoxic/hypoxic zone for denitrification. Decentralized, advanced N-removal onsite wastewater treatment systems (OWTS) are used to mitigate the impact of excess N from wastewater on receiving waters, which includes eutrophication, fish and shellfish kills, and threats to public health (Carpenter et al, 1998; Sohail & Adeloju, 2016; Ward et al, 2005). Recent studies have shown that non-biogenic CO2 emissions from various C-containing household and personal care products can significantly contribute to GHG emissions from WTPs, and should be included in emissions analysis (Griffith, et al, 2009; Law et al, 2013; Tseng et al, 2016)
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