title: Modeling Nitrogen Losses in Conventional and Advanced Soil-Based Onsite Wastewater Treatment Systems under Current and Changing Climate Conditions.
abstract: Most of the non-point source nitrogen (N) load in rural areas is attributed to onsite wastewater treatment systems (OWTS). Nitrogen compounds cause eutrophication, depleting the oxygen in marine ecosystems. OWTS rely on physical, chemical and biological soil processes to treat wastewater and these processes may be affected by climate change. We simulated the fate and transport of N in different types of OWTS drainfields, or soil treatment areas (STA) under current and changing climate scenarios, using 2D/3D HYDRUS software. Experimental data from a mesocosm-scale study, including soil moisture content, and total N, ammonium (NH4+) and nitrate (NO3-) concentrations, were used to calibrate the model. A water content-dependent function was used to compute the nitrification and denitrification rates. Three types of drainfields were simulated: (1) a pipe-and-stone (P&S), (2) advanced soil drainfields, pressurized shallow narrow drainfield (PSND) and (3) Geomat (GEO), a variation of SND. The model was calibrated with acceptable goodness-of-fit between the observed and measured values. Average root mean square error (RSME) ranged from 0.18 and 2.88 mg L-1 for NH4+ and 4.45 mg L-1 to 9.65 mg L-1 for NO3- in all drainfield types. The calibrated model was used to estimate N fluxes for both conventional and advanced STAs under current and changing climate conditions, i.e. increased soil temperature and higher water table. The model computed N losses from nitrification and denitrification differed little from measured losses in all STAs. The modeled N losses occurred mostly as NO3- in water outputs, accounting for more than 82% of N inputs in all drainfields. Losses as N2 were estimated to be 10.4% and 9.7% of total N input concentration for SND and Geo, respectively. The highest N2 losses, 17.6%, were estimated for P&S. Losses as N2 increased to 22%, 37% and 21% under changing climate conditions for Geo, PSND and P&S, respectively. These findings can provide practitioners with guidelines to estimate N removal efficiencies for traditional and advanced OWTS, and predict N loads and spatial distribution for identifying non-point sources. Our results show that N losses on OWTS can be modeled successfully using HYDRUS. Furthermore, the results suggest that climate change may increase the removal of N as N2 in the drainfield, with the magnitude of the effect depending on a drainfield type.
authors.affiliation: Department of Civil and Environmental Engineering, University of Rhode Island, Kingston, Rhode Island, United States of America.
authors.forename: Ivan
authors.initials: I
authors.lastname: Morales
authors.affiliation: Laboratory of Soil Ecology and Microbiology, University of Rhode Island, Kingston, Rhode Island, United States of America.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Cooper
authors.affiliation: Laboratory of Soil Ecology and Microbiology, University of Rhode Island, Kingston, Rhode Island, United States of America.
authors.forename: José A
authors.initials: JA
authors.lastname: Amador
authors.affiliation: Department of Civil and Environmental Engineering, University of Rhode Island, Kingston, Rhode Island, United States of America.|Department of Geosciences, University of Rhode Island, Kingston, Rhode Island, United States of America.
authors.forename: Thomas B
authors.initials: TB
authors.lastname: Boving
mesh_terms: D064751:Ammonium Compounds / Q000737:chemistry; D002138:Calibration; D002980:Climate; D057231:Climate Change; D003198:Computer Simulation; D058440:Denitrification; D004553:Electric Conductivity; D004784:Environmental Monitoring; D005068:Eutrophication; D060587:Groundwater / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D009566:Nitrates / Q000737:chemistry; D009584:Nitrogen / Q000032:analysis* / Q000737:chemistry; D010100:Oxygen / Q000737:chemistry; D012984:Software; D012987:Soil / Q000737:chemistry*; D014865:Waste Disposal, Fluid / Q000379:methods; D062065:Wastewater / Q000032:analysis*; D014874:Water Pollutants, Chemical / Q000032:analysis; D018508:Water Purification / Q000379:methods*
chemical_list: D064751:Ammonium Compounds; D009566:Nitrates; D009584:Nitrogen; D010100:Oxygen; D012987:Soil; D062065:Wastewater; D014874:Water Pollutants, Chemical