Infiltration of Wastewater in a Newly Started Pilot Sand‐Filter System: I. Reduction of Organic Matter and Phosphorus

The objective of the study was to monitor variables on P and organic matter reduction related to the wastewater purification process in a sand‐filter system constructed according to the directives issued by the National Swedish Environment Protection Board. Monitoring was conducted from start‐up until a steady state was reached. The system consists of a three‐chambered septic tank, a pilot sand‐filter, corresponding to the demand for one person, and eight sand‐filter columns. It was loaded with 67 L m−2 d−1 of an artificial wastewater. The effluent from the septic tank reached a steady state with respect to the chemical oxygen demand (COD) and P levels after 3 wk. By Day 78 the cumulative load of COD and P had been reduced by 37 and 48%, respectively. In the sand filter the reduction in COD started immediately and concentrations in the effluent remained low and steady from Day 18 until Day 78 when the last sampling was made. The total reduction in COD amounted to 91%. Effluent concentrations of P were initially low but increased as the experimental period progressed. The total decrease in P in the sand filter was 83%. The reduction in COD was highest in the upper 1.5 cm of the sand profile and was almost complete after 15 cm of infiltration; in contrast, P levels showed an overall decrease throughout the sand profile. The columns were less efficient at reducing COD but more efficient at decreasing P compared with the sand filter. The results from the columns suggest that anaerobic conditions had developed.