Gurpal S. Toor

δ15N and δ18O Reveal the Sources of Nitrate-Nitrogen in Urban Residential Stormwater Runoff

Nitrogen (N) sources are widely distributed in the complex urban environment. High-resolution data elucidating N sources in the residential catchments are not available. We used stable isotopes of N and oxygen (O) of nitrate (δ(18)O-NO3(-) and δ(15)N-NO3(-)) along with δ(18)O and hydrogen (δD) of water (H2O) to understand the sources and transformations of N in residential stormwater runoff. Stormwater runoff samples were collected over 25 stormwater events at 5 min intervals using an autosampler installed at the residential catchment outlet pipe that drained 31 low-density homes with a total drainage area of 0.11 km(2). Bayesian mixing model results indicated that atmospheric deposition (range 43-71%) and chemical N fertilizers (range <1-49%) were the dominant NO3-N sources in the stormwater runoff and that there was a continuum of source changes during the stormwater events. Further, the NO3-N transport in the stormwater runoff from the residential catchment was driven by mixing of multiple sources and biotic (i.e., nitrification) processes. This work suggests that a better understanding of N transport and sources is needed to reduce N export and improve water quality in urban water systems.

Dissolved organic nitrogen in urban streams: Biodegradability and molecular composition studies.

A portion of the dissolved organic nitrogen (DON) is biodegradable in water bodies, yet our knowledge of the molecular composition and controls on biological reactivity of DON is limited. Our objective was to investigate the biodegradability and molecular composition of DON in streams that drain a gradient of 19-83% urban land use. Weekly sampling over 21 weeks suggested no significant relationship between urban land use and DON concentration. We then selected two streams that drain 28% and 83% urban land use to determine the biodegradability and molecular composition of the DON by coupling 5-day bioassay experiments with high resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). Both urban streams contained a wide range of N-bearing biomolecular formulas and had >80% DON in lignin-like compounds, with only 5-7% labile DON. The labile DON consisted mostly of lipid-and protein-like structures with high H/C and low O/C values. Comparison of reactive formulas and formed counterparts during the bioassay experiments indicated a shift toward more oxygenated and less saturated N-bearing DON formulas due to the microbial degradation. Although there was a little net removal (5-7%) of organic-bound N over the 5-day bioassay, there was some change to the carbon skeleton of DON compounds. These results suggest that DON in urban streams contains a complex mixture of compounds such as lipids, proteins, and lignins of variable chemical structures and biodegradability.

Biodegradability and Molecular Composition of Dissolved Organic Nitrogen in Urban Stormwater Runoff and Outflow Water from a Stormwater Retention Pond

Dissolved organic nitrogen (DON) can be a significant part of the reactive N in aquatic ecosystems and can accelerate eutrophication and harmful algal blooms. A bioassay method was coupled with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) to determine the biodegradability and molecular composition of DON in the urban stormwater runoff and outflow water from an urban stormwater retention pond. The biodegradability of DON increased from 10% in the stormwater runoff to 40% in the pond outflow water and DON was less aromatic and had lower overall molecular weight in the pond outflow water than in the stormwater runoff. More than 1227 N-bearing organic formulas were identified with FT-ICR-MS in the stormwater runoff and pond outflow water, which were only 13% different in runoff and outflow water. These molecular formulas represented a wide range of biomolecules such as lipids, proteins, amino sugars, lignins, and tannins in DON from runoff and pond outflow water. This work implies that the urban infrastructure (i.e., stormwater retention ponds) has the potential to influence biogeochemical processes in downstream water bodies because retention ponds are often a junction between the natural and the built environment.

Septic systems as hot-spots of pollutants in the environment: Fate and mass balance of micropollutants in septic drainfields

Septic systems, a common type of onsite wastewater treatment systems, can be an important source of micropollutants in the environment. We investigated the fate and mass balance of 17 micropollutants, including wastewater markers, hormones, pharmaceuticals and personal care products (PPCPs) in the drainfield of a septic system. Drainfields were replicated in lysimeters (1.5m length, 0.9m width, 0.9m height) and managed similar to the field practice. In each lysimeter, a drip line dispersed 9L of septic tank effluent (STE) per day (equivalent to 32.29L/m(2) per day). Fourteen micropollutants in the STE and 12 in the leachate from drainfields were detected over eight months. Concentrations of most micropollutants in the leachate were low (<200ng/L) when compared to STE because >85% of the added micropollutants except for sucralose were attenuated in the drainfield. We discovered that sorption was the key mechanism for retention of carbamazepine and partially for sulfamethoxazole, whereas microbial degradation likely attenuated acetaminophen in the drainfield. This data suggests that sorption and microbial degradation limited transport of micropollutants from the drainfields. However, the leaching of small amounts of micropollutants indicate that septic systems are hot-spots of micropollutants in the environment and a better understanding of micropollutants in septic systems is needed to protect groundwater quality.

Micropollutants in groundwater from septic systems: Transformations, transport mechanisms, and human health risk assessment

Septic systems may contribute micropollutants to shallow groundwater and surface water. We constructed two in situ conventional drainfields (drip dispersal and gravel trench) and an advanced drainfield of septic systems to investigate the fate and transport of micropollutants to shallow groundwater. Unsaturated soil-water and groundwater samples were collected, over 32 sampling events (January 2013 to June 2014), from the drainfields (0.31-1.07xa0m deep) and piezometers (3.1-3.4xa0m deep). In addition to soil-water and groundwater, effluent samples collected from the septic tank were also analyzed for 20 selected micropollutants, including wastewater markers, hormones, pharmaceuticals and personal care products (PPCPs), a plasticizer, and their transformation products. The removal efficiencies of micropollutants from septic tank effluent to groundwater were similar among three septic systems and were 51-89% for sucralose and 53->99% for other micropollutants. Even with high removal rates within the drainfields, six PPCPs and sucralose with concentrations ranging from <0.3 to 154xa0ng/L and 121 to 32,000xa0ng/L reached shallow groundwater, respectively. The human health risk assessment showed that the risk to human health due to consumption of groundwater is negligible for the micropollutants monitored in the study. A better understanding of ecotoxicological effects of micropollutant mixtures from septic systems to ecosystem and human health is warranted for the long-term sustainability of septic systems.

High Removal of Effluent-borne Nitrogen with Multiple External Electron Donors in the Engineered Drainfield of an Advanced Septic System

Septic systems can be a major source of nitrogen (N) in shallow groundwater. We designed an in situ engineered drainfield with aerobic-anaerobic (sand-woodchips) and anaerobic (elemental sulfur-oyster shell) media to remove N in the vadose zone and reduce N transport to groundwater. Effluent was dispersed on top of the engineered drainfield (3.72 m infiltrative surface) and then infiltrated through the aerobic-anaerobic and anaerobic media before reaching natural soil. Water samples were collected over 64 sampling events (May 2012-December 2013) from three parts of the drainfield: (i) a suction cup lysimeter installed at the sand-woodchips interface, (ii) a pipe after effluent passed through the aerobic-anaerobic media, and (iii) a tank containing anaerobic media. In the effluent, most of the total N (66 mg L) was present as NH-N (88.8%), whereas at the sand-woodchips interface the dominant N form was NO-N (31 mg L; 85% of total N). As the effluent passed through the aerobic-anaerobic media in the drainfield, heterotrophic denitrification reduced NO-N to 5.4 mg L. In the tank containing anaerobic media, autotrophic denitrification, facilitated by elemental sulfur, further reduced NO-N to 1 mg L. Overall, 90% of total added N was removed as the effluent passed through the aerobic-anaerobic and anaerobic media within the engineered drainfield. We conclude that the use of multiple electron donors from external media (sand-woodchips and elemental sulfur-oyster shell) was effective at removing N in the engineered drainfield and will reduce the risk of groundwater N contamination from septic systems in areas with shallow groundwater.

Mass Balance of Water and Nitrogen in the Mounded Drainfield of a Drip-Dispersal Septic System.

Quantitative assessment of nitrogen (N) loading from septic systems is needed to protect groundwater contamination. We determined the mass balance of water and N in the mounded drainfield of a drip-dispersal septic system. Three lysimeters (152.4 cm long, 91.4 cm wide, 91.4 cm high, with 1:1 side slope) were constructed using pressure-treated wood to mimic mounded drainfields. Of total water inputs, septic tank effluent (STE) added 57% water and natural rainfall added 43% water from January 2013 to January 2014. Outputs included leached water (46%) from the lysimeters over 67 sampling events ( = 15 daily and = 52 weekly flow-weighted), potential evapotranspiration (28%), and water stored in the drainfields (26%). Over 13 mo, each drainfield received 227 g of total N (STE, 99%; rainfall, 1%), of which 33% leached, 23% accumulated in the drainfield, and 6% was taken up by grass, with the remainder (38%) estimated to be gaseous N loss. Using these data, the leaching of water from 2.5 million drip-dispersal drainfields in the state of Florida was estimated to be 2.29 × 10 L yr, which would transport 2.4 × 10 kg of total N yr from the drainfields to shallow groundwater. Further reduction of N below drainfields in the soil profile could be expected before STE reaches groundwater. Our results provide quantitative information on the water and N loading and can be used to optimize drainfield conditions to attenuate N and protect groundwater quality.

A review of the fate and transport of nitrogen, phosphorus, pathogens, and trace organic chemicals in septic systems

ABSTRACT A large population living in suburban and rural areas in the world uses septic systems, also called onsite wastewater treatment systems, to dispose of household wastewater. In a conventional septic system, the wastewater flows from a household to a septic tank, where solids settle and a clarified effluent is produced. This effluent is dispersed into the soil for further treatment and can be a potential source of various contaminants such as nutrients, pathogens, and a new class of compounds known as trace organic chemicals (TOrCs) in shallow groundwater and surface waters. We review the current state of the science on the fate and transport of three groups of contaminants—nutrients (nitrogen, phosphorus), pathogens, and TOrCs—and water quality impacts associated with these contaminants in conventional septic systems. We also discuss alternative technologies that may be employed when site conditions or environmental needs preclude the use of conventional septic systems.

Fate, mass balance, and transport of phosphorus in the septic system drainfields

Septic systems can be a potential source of phosphorus (P) in shallow groundwater. Our objective was to investigate the fate, mass balance, and transport of P in the drainfield of a drip-dispersal septic system. Drainfields were replicated in lysimeters (152.4xa0cm long, 91.4xa0cm wide, and 91.4xa0cm high). Leachate and effluent samples were collected over 67 events (nxa0=xa015 daily; nxa0=xa052 weekly flow-weighted) and analyzed for total P (TP), orthophosphate (PO4P), and other P (TP - PO4P). Mean TP was 15xa0mgxa0L(-1) (84% PO4P; 16% other P) in the effluent and 0.16xa0mgxa0L(-1) (47% PO4P, 53% other P) in the leachate. After one year, 46.8xa0g of TP was added with effluent and rainfall to each drainfield, of which, <1% leached, 3.8% was taken up by St. Augustine grass, leaving >95% in the drainfield. Effluent dispersal increased water extractable P (WEP) in the drainfield from <5 to >10xa0mgxa0kg(-1). Using the P sorption maxima of sand (118xa0mgxa0kg(-1)) and soil (260xa0mgxa0kg(-1)), we estimated that ∼18% of the drainfield P sorption capacity was saturated after one year of effluent dispersal. We conclude that despite the low leaching potential of P dispersed with effluent in the first year of drainfield operation, a growing WEP pool in the drainfield and low P sorption capacity of Floridas sandy soils may have the potential to transport P to shallow groundwater in long-running septic systems.

Managing urban runoff in residential neighborhoods: Nitrogen and phosphorus in lawn irrigation driven runoff

Sources and mechanisms of nutrient transport in lawn irrigation driven surface runoff are largely unknown. We investigated the transport of nitrogen (N) and phosphorus (P) in lawn irrigation driven surface runoff from a residential neighborhood (28 ha) of 56% impervious and 44% pervious areas. Pervious areas encompassing turfgrass (lawns) in the neighborhood were irrigated with the reclaimed water in common areas during the evening to late night and with the municipal water in homeowner’s lawns during the morning. The stormwater outlet pipe draining the residential neighborhood was instrumented with a flow meter and Hach autosampler. Water samples were collected every 1-h and triple composite samples were obtained at 3-h intervals during an intensive sampling period of 1-week. Mean concentrations, over 56 sampling events, of total N (TN) and total P (TP) in surface runoff at the outlet pipe were 10.9±6.34 and 1.3±1.03 mg L–1, respectively. Of TN, the proportion of nitrate–N was 58% and other–N was 42%, whereas of TP, orthophosphate–P was 75% and other–P was 25%. Flow and nutrient (N and P) concentrations were lowest from 6:00 a.m. to noon, which corresponded with the use of municipal water and highest from 6:00 p.m. to midnight, which corresponded with the use of reclaimed water. This data suggests that N and P originating in lawn irrigation driven surface runoff from residential catchments is an important contributor of nutrients in surface waters.