Constructed wetlands as an appropriate treatment of landfill leachate.
Bricken, Elizabeth Colomb.
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One of the main environmental problems associated with the disposal of waste on land is the release of liquid emissions from the site. This wastewater, known as leachate, is a product of the biodecomposition of the waste and filtrates from the landfill once the moisture saturation of the fill has been reached. The chemical composition of leachate is variable over time and between sites. Regardless of these variables, the main pollutants of concern in the leachate are ammonia and organics, both of which can cause environmental degradation in relatively low concentrations. Worldwide and in South Africa, leachate has either been directly released into the environment or into the local domestic sewage system. As more has been learned about the human and environmental health risks associated with these disposal methods, there has been a new focus in waste management toward treating the leachate at the source as part of the broader focus of sustainable landfilling. One of the treatment options being used is constructed wetlands (CW) due to the physical and chemical transformation mechanisms in these biological systems. This treatment process has been demonstrated to be effective as a final polishing treatment for leachate, and it is considered a technology appropriate in the South African context. Therefore the aim of dissertation is to ascertain the use of constructed wetlands as an appropriate treatment option for untreated methanogenic landfill leachate by determining the efficiency of ammonia and organic removal in a pilot-scale vegetated submerged bed (VSB) constructed wetland (CW) planted with Phragmites australis. During the 22-week treatability trial the VSB achieved an ammonia concentration removal efficiency of 91% and mass removal efficiency of 87%. Despite this substantial reduction of ammonia, the VSB was unable to achieve the required discharge standard. There were erratic fluctuations in both the treatment efficiencies for COD and BOO, and the results show no evidence of constant reduction of organics during the treatability trials. This is due to the refractory nature and the low biodegradability of the organics that remain in methanogenic leachate as suggested by the low BOO to COD ratio. Due to the low biodegradability of the organics, a biological treatment system, such as a VSB, will not be able to reliably meet the required discharge standards. Other passive treatment options or a combination of systems need to be explored in order to both satisfy legislative requirements and be appropriate in the South African context.