A comparison of parallel and serial distribution of septic tank effluent

Parallel and serial distribution of septic tank effluent onto filter fields were compared during the period of September 1985 to August 1986. The study was performed to determine if any difference exists between the two wastewater distribution systems with respect to hydraulic transmission and renovation efficiency through a filter field. Soil columns were used to model filter fields loaded in either a parallel or serial fashion. A distribution system was constructed to load septic tank effluent onto the columns in a precise manner. Column drainage conditions were either freely drained or saturated, so as to simulate the extreme ranges encountered in an actual situation. Effluent from the filter field models was collected weekly and analyzed for the concentration of organics, phosphorus, and nitrogen as well as for fecal coliform populations and the volume of drainage. These parameters were investigated to determine if there were any differences between the distribution types. The investigation showed that parallel distribution is superior to serial for prevention of a high rate discharge episode under a freely drained treatment. Also, parallel distribution is superior in the removal of phosphorus and fecal coliforms for a freely drained condition. For a saturated condition parallel is superior to serial in the removal of nitrogen. For all the treatments investigated serial distribution was never superior to parallel distribution.