The filter system for tertiary treatment of sewage effluent by land application--its performance in a subtropical environment.

FILTER is an innovative, CSIRO developed system for treating effluent using high rate land application and subsequent effluent recapture via a closely spaced, subsurface drainage network. We report on the summer performance of a FILTER system established in a subtropical environment on a relatively impermeable swelling clay soil underlain by a deep regional water table. Using secondary treated sewage effluent, the FILTER system produced effluent of tertiary nutrient standards (< or = 5 mg/L TN; < or = 1 mg/L TP), with salinity levels suitable for subsequent irrigation reuse (EC < or = 2.5 dS/m). Removal of faecal coliforms was considerably less effective. The hydraulic loading rate achieved was about two and a half times large than conventional irrigation demand, but this was associated with high deep percolation losses (c 3 mm/day). Comparisons are made with the original FILTER system developed and tested by Jayawardane et al. in temperate Australia. Suggestions are made for modifications to, and further testing of FILTER in a subtropical environment.