USE OF UNDISTURBED SOIL COLUMNS TO EVALUATE SOIL CAPABILITY TO RENOVATE ON-SITE SEWAGE TREATMENT SYSTEM EFFLUENT

The objective of this study was to assess soil capability for the renovation of effluent from on-site sewage treatment systems for a number of different soil types commonly present in Queensland, Australia. Undisturbed soil cores from 12 different sites were collected by a hollow hydraulic auger to a depth of approximately 1400mm. Primary treated sewage effluent with the following characteristics; 8.2 mg/L as NO3-N, 0.79 mg/L as PO43-, pH 7.89, EC 0.9 ds/m and COD 185 mg/L was applied to the soil columns. Due to the heterogeneity of the soil structure and its chemical characteristics, the soil capability for removing effluent contaminants varied widely. The results for the sandy soil types reported an 80 % removal in the nitrate, phosphorus and salt content after 240mL flow; then the concentration of nutrients started to increase significantly in effluent samples collected from the lower section of the sandy soil columns. The wash-off of the accumulated salts and ammonia fixation resulting from the high organic matter content in this region of the columns. The soils with heavy clay content and a high cation exchange capacity provided 95 % nitrate and total phosphorus removal and 50 % salt reduction in the first few centimetres of the columns. Also, some soils were relatively impermeable due to the amount an