Phosphorus Movement in Soils: Theoretical Aspects
1975
The renovation of waste water by land application shows promise because of the potential to use certain waste water nutrients to fertilize agricultural crops and to recycle these nutrients as agricultural products. In order to locate, design, and manage land treatment processes, quantitative descriptions of critical processes are required. The adsorption of P by soils is a critical process which needs to be considered. This paper compares a new model for P movement in soils with existing adsorption-desorption models developed for chromatography and ion exchange processes. The effect of the model parameters on P movement in soils is also examined. From the new model considered here, it was found that under P adsorption, a P profile of fixed shape (shock layer) developed and moved through the soil at a speed which could be calculated from the P Langmuir adsorption isotherm, density of the soil, and the P rate of application to the soil. Model parameters have an effect on the shape of the P profile, but over the range of condition studied here, the S-shape P front (shock layer) was less than 4 cm in thickness. The range of conditions were chosen to cover a range of soils and operating conditions which might be considered during the selection and design of a waste water land treatment process. It should not be construed from this study, that a small shock layer exists for all adsorption cases, or for the case of desorption of P from soils during leaching.
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