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

摘要

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 (152.4 cm long, 91.4 cm wide, and 91.4 cm high). Leachate and effluent samples were collected over 67 events (n = 15 daily; n = 52 weekly flow-weighted) and analyzed for total P (TP), orthophosphate (PO4-P), and other P (TP-PO4-P). Mean TP was 15 mg L-1 (84% PO4-P; 16% other P) in the effluent and 0.16 mg L-1 (47% PO4-P, 53% other P) in the leachate. After one year, 46.8 g 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 >10 mg kg(-1). Using the P sorption maxima of sand (118 mg kg(-1)) and soil (260 mg kg(-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 Florida's sandy soils may have the potential to transport P to shallow groundwater in long-running septic systems. (C) 2016 Elsevier Ltd. All rights reserved.