The role of soils in the removal of total coliforms from domestic wastewater

The removal of microorganisms from domestic wastewater as it contacts the soil is an important consideration in land disposal systems. In this study, a field model was developed to investigate the removal efficiency of total coliforms from domestic wastewater by infiltration through porous media. The model consisted of an inlet chamber, a channel of 25 m long and an outlet chamber. The channel was sequencially filled with sand type I(d_eff:0.55 mm), sand type II(d_eff:3.25 mm) and with crushed stone (d_eff:10 mm). The coliform removal by infiltration through porous media was investigated with respect to service time and distance. The overall coliform removal achieved varied as 79%, 73% and 55.6% respectively for the three porous media of increasing effective grain sizes. Experimental data indicated that the removal efficiency depends basicly on the distance travelled and not on time. The reduction of coliform counts with distance was also defined by a first order reaction kinetics and the rate constants were determined by applying the least square technique. Slower rate constants were calculated for increasing effective grain sizes. In conclusion, it was observed that, even though the rapid infiltration is the least efficient system compared with the other land treatment systems, sufficient removal was observed considering the microbiological quality of the wastewater.