Leachate Management - Liquid Waste Treatment

Nitrification Roughing Filter and Gravel Beds

The leachate passes first through a roughing filter containing limestone then through a gravel filter bed containing inert media. The roughing filter adds additional alkalinity to the leachate and potentially removes further metals. Naturally occurring bacteria on the surface of the gravel bed filter further reduce ammonium levels and residual BOD.

RAPS (Reducing and Alkalinity Producing System)

Leachate from Stage 2 flows vertical through a bed of limestone chippings mixed with cow manure. Sulphates are removed by sulphate reducing bacteria and insoluble sulphides of heavy metals (Zinc, Nickel, Lead, Copper and Cadmium) are formed.

Leachate from the RAPS flows over aeration cascade steps use to re-oxygenate the leachate prior to the next stage of treatment.

Reed Beds

Following the anaerobic RAPS the leachate passes through a horizontal flow reed bed for polishing treatment. The reed bed volatises and nitrifies residual ammonium, denitrifies nitrates to nitrogen and raises the dissolved oxygen level in the leachate slightly. The reed bed also provides polishing treatment to remove residual BOD and metals by a combination of deposition/ filtering in the bed and uptake into the reed rhizomes and leaves of the reeds.

Wetlands

Following the reed beds the leachate quality is passed through a series of wetlands prior to being released to the Seal Sands Estuary. The wetlands will comprise of five lagoons in series, offering buffering of the leachate prior discharge to the environment. Some with shallow shelf edges are to be planted with natural wetland vegetation.