Effectiveness of Advanced Nitrogen-Removal Onsite Wastewater Treatment Systems in a New England Coastal Community

Bianca N. Ross,Kevin P. Hoyt,George W. Loomis,Jose A. Amador

doi:10.1007/s11270-020-04911-5

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; however, few studies have assessed their effectiveness. We evaluated the total N (TN) concentration of effluent from 50 advanced N-removal OWTS in Charlestown, Rhode Island, USA for 3 years. We quantified differences in effectiveness as a function of N-removal technology and home occupancy pattern (seasonal vs. year-round use), and examined the relationship between wastewater properties and TN concentration. 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’s regulatory standard for effluent TN concentration (19 mg N/L) was highest for RX30 systems (78%), followed by AX20 (73%), FAST (67%), and Norweco (0%). Occupancy pattern did not affect effluent TN concentration. Variation in TN concentration was driven by ammonium and nitrate for all technologies, and also by temperature for FAST and pH for Norweco. Median daily (g N/day) and annual (kg N/yr) N loads were significantly higher for year-round (5.3 and 2.3) than for seasonal (3.7 and 0.41) systems, likely due to differences in volume of wastewater treated. Our results suggest that advanced N-removal OWTS vary in their compliance with the state regulatory standard for effluent TN and can withstand long periods of non-use without compromising effectiveness. Nevertheless, systems used year-round do produce a higher daily and annual N load than seasonally-used systems.

Highlights

Effluent from onsite wastewater treatment systems (OWTS) is an important source of nitrogen (N) to coastal watersheds (Valiela et al, 2010)
We worked with the Rhode Island Department of Environmental Management (RIDEM) and the Town of Charlestown Onsite Wastewater Management department to identify sites that rely on well water for potable water and use a pressurized pump to discharge effluent to the soil treatment area (STA)
When values for all sampling events and both occupancy patterns are considered, 78% of RX30 systems produced effluent with a median total N (TN) concentration of ≤ 19 mg N/L, followed by AX20 (73%), FAST (67%), and Norweco (0%) (Fig. 2)

Summary

Introduction

Effluent from onsite wastewater treatment systems (OWTS) is an important source of nitrogen (N) to coastal watersheds (Valiela et al, 2010). Because N is a limiting nutrient in coastal ecosystems, increased inputs of N to groundwater and poorly flushed coastal systems promote eutrophication, which results in anoxia that kills fish and shellfish. Compromising the health of coastal waterbodies threatens environmental and public health as well as the economy, through mandated beach closures and financial losses in the fish and shellfish trade (Gan, 2002). Residential wastewater can contaminate groundwater with nitrate and pathogens (Ward et al, 2005; Lancellotti et al, 2017)

Methods

Results

Conclusion