Oxygen Relationships in Intermittent Sand Filtration

A model for processes in intermittent sand filtration is described and an expression for oxygen transfer is formulated. The model assumes that aerobic bacterial activity within the sand or soil matrix is limited by oxygen deficiency while the surface is ponded. Atmospheric oxygen reenters into the soil after infiltration ends. Aerobic activity is resumed, but oxygen penetration is limited and some depths may be always anaerobic. This condition leads to large variations in the concentration of certain contaminants in the percolate. Analyses of soil moisture in field studies and of effluent from laboratory sand columns substantiated the model. The oxygen content at sufficiently long times after addition of wastes can be described by a quasi steady-state diffusion equation including a term for an oxygen sink. Measurements of oxygen content during laboratory and field studies show that the oxygen profile changes only slightly up to two days after the quasi-steady state is attained. Results can be applied in operating existing facilities and in interpreting data from pilot-plant studies.