USE OF PHYTOCAPS IN REMEDIATION OF CLOSED LANDFILLS

Abstract The suitability of a phytocap as an alternate capping system in the management of closed landfills was investigated. A field trial involving a range of native trees, shrubs and grasses, irrigated with landfill leachate of varying strength was undertaken at the former Nudgee Landfill. Laboratory and field-testing evaluated the effect of leachate on soil physical and chemical properties, and on plant performance. Changes in key soil physical properties (aggregate stability, hydraulic conductivity and infiltration) resulted from the application of leachate. Leachate significantly affected the survival and growth rates of many of the plant species. This trial has provided important information on design of phytocaps, and the incorporation of leachate-tolerant plant species in landfill management. Additional Keywords: nitrogen, carbon, hydraulic properties, aggregation, landfill leachate, capping systems Introduction Leachate management continues to be one of the major issues facing regulatory authorities responsible for remediation of closed landfills. Various strategies for minimising leachate release into the environment can be engineered into landfill design such as drainage collection systems, cut-off walls, reactive permeable barriers, collection and recirculation systems, and the construction of low-permeability (engineered) surface caps. Engineered caps have been widely used as an effective method to minimise water entry into landfills, and consequently, the potential for leachate generation. Recently, less-costly capping designs that incorporate leachatetolerant plants have been investigated as an alternate capping system to engineered caps. These alternative designs involve planting trees and shrubs directly into the landfill cover material, or into a thin layer of topsoil (approx. 30 cm) above the landfill cover, and have been termed "phytoremediation caps (or phytocaps)". The phytocap principally involves the use of plants that are tolerant to highly saline, ammonium-rich leachate, and is closely related to the established remediation technology referred to as "phytoremediation"