Nutrient transport and transformation beneath an infiltration basin

Abstract

Field experiments were conducted to examine nutrient transport and transformation beneath an infiltration basin used for the disposal of treated wastewater. Removal of nitrogen from infiltrating water by denitrification was negligible beneath the basin, probably because of subsurface aeration as a result of daily interruptions in basin loading. Retention of organic nitrogen in the upper 4.6 m of the unsaturated zone (water table depth of approximately 11 m) during basin loading resulted in concentrations of nitrate as much as 10 times that of the applied treated wastewater, following basin “rest” periods of several weeks, which allowed time for mineralization and nitrification. Approximately 90% of the phosphorus in treated wastewater was removed within the upper 4.6 m of the subsurface, primarily by adsorption reactions, with abundant iron and aluminum oxyhydroxides occurring as soil coatings. A reduction in the flow rate of infiltrating water arriving at the water table may explain the accumulation of relatively coarse (>0.45 μm), organic forms of nitrogen and phosphorus slightly below the water table. Mineralization and nitrification reactions at this second location of organic nitrogen accumulation contributed to concentrations of nitrate as much as three times that of the applied treated wastewater. Phosphorus, which accumulated below the water table, was immobilized by adsorption or precipitation reactions during basin rest periods.

Comparison of a modified and traditional rapid infiltration basin for treatment of nutrients in wastewater effluent

“…At these low concentrations (values below 1 mg/L), the ability to ascertain actual removal efficiencies was difficult as the values were at the threshold detection limit. The observed rise in NO x could be due to nitrification as was noted by Sumner and Bradner (), in their prior work. However, increased TKN values exiting the RIB as compared to input values suggest dissimilatory nitrate reduction to ammonia.…”

Assessing Potential Impacts of a Wastewater Rapid Infiltration Basin System on Groundwater Quality: A Delaware Case Study

“…Nitrogen and P loads from advanced sequenced batch reactor systems designed to discharge nitrifi ed effl uents with 10 mg L −1 of NO 3 − -N and 3 mg L −1 total P would be lower (1000-2000 and 600-200 kg ha −1 yr −1 for total N and P, respectively) but still far greater than typical nutrient loading rates to agricultural cropland in Delaware (100-250 kg N ha −1 yr −1 and 5-100 kg P ha −1 yr −1 , Sims and Gartley, 1996). With such loading rates and concentrations, it is not surprising that some studies have documented high concentrations of NH 4 + -N, NO 3 − -N, and P in groundwater directly under and hundreds to thousands of meters downgradient of RIBS (Koerner and Haws, 1979;LeBlanc, 1984;McCobb et al, 2002;Sumner and Bradner, 1996).…”

Weighing Lysimeters for Evapotranspiration Research in a Humid Environment

“…Additionally, Gregory et al (2006) reported that the infiltration rate is 225 mm/h for the pasture site where the lysimeters are located. For soil with a high infiltration rate, surface runoff into the lysimeters is minimal because the lateral flow movement is negligible compared to vertical flow (Sumner and Bradner, 1996). Furthermore, the lysimeters are located at a relatively higher land surface within the field.…”