Author(s)

I. Vogeler, R. Cichota & F. Witing

Abstract

Worldwide, large quantities of wastewater are produced, including municipal effluent, dairy-shed effluent, and wastewater from factories. Most wastewater is treated to remove solids and contaminants. But even treated wastewater may still contain organic matter and high levels of nutrients, such as nitrogen and phosphorus (P). To assess the feasibility of effluent disposal to land with respect to P leaching to groundwater and build up at the soil surface leaching experiments were performed in the laboratory and in the field. The soil used for the study was the Kawhatau stony silt loam from New Zealand. In the laboratory undisturbed soil columns were leached under steady unsaturated flow conditions using either wastewater, or solutions containing 6 or 60 ppm of phosphorus. In the field drainage lysimeters were irrigated with wastewater or a solution containing 60 ppm at a rate of 30 mm/day. Results from the leaching study in the laboratory show that after an infiltration equivalent to about 1 year of application, the P concentration in the in drainage water was below 0.4 ppm, regardless of the input concentration. Thus under the unsaturated, steady state flow conditions, the silt loam adsorbed all the applied P. In the field P concentrations in the drainage water after 2500 mm of wastewater application were below 0.3 ppm in all lysimeters, except one, where preferential flow occurred and P concentrations reached 2 ppm. A model, based on the convection dispersion equation, simply linked with the Freundlich adsorption isotherm could not be used successfully to describe the build up and movement of P in the soil. Keywords: P leaching , CDE dispersion equation, Freundlich isotherm.

Keywords

P leaching , CDE dispersion equation, Freundlich isotherm