GROUNDWATER RECHARGE OF SEWAGE EFFLUENT THROUGH AMENDED SAND

The performance of a groundwater recharge basin at the Kwinana Groundwater Recharge Site in Western Australia was monitored between 1983 and 1986. A primary aim of the monitoring programme was to study the improvement in the removal of faecal coliforms and nutrients (nitrogen and phosphorus) by amending the sand of the recharge basin with gypsum-neutralized red mud (fine bauxite refining residue). The study consisted of five operating stages. Stage 1 was a baseline study using unamended sand. Stages 2-5 were after sand amendment with red mud. Continuous flooding and flooding/drying regimes were studied with primary effluent or a mixture of primary and secondary effluents. Phosphorus removal was maintained at a high level (over 80%) in all of the stages after the sand amendment. Faecal coliform removal was generally excellent, except at the beginning of each stage when primary effluent was used, and only a thousand-fold reduction was achieved. Removal improved with time and most monitored bore samples contained no faecal coliforms/100 ml. With one exception the groundwater met water quality criteria for irrigation. Nitrogen removal of approx. 45% was obtained with primary effluent using a cycle of flooding and drying (stage 3). Continuous flooding with primary effluent (stage 5) did not improve denitrification. No nitrogen removal was observed with a mixture of two-thirds secondary effluent and one-third primary effluent.