Constructed wetland for landfill leachate treatment
Production of leachate, as result of infiltration and runoff taking place inside the landfill, has always represented one of the most important matters of environmental impact of landfills. This is primarily due to the extreme variability of substances present in the landfill, and therefore to the high heterogeneity of leachate's composition.
In most cases, leachate is treated externally of the landfill, convoying it to comunity wastewater treatment plant. However, in the last years had become greater the interest for in situ treatment plants, because of the possible advantages, like: elimination of costs and risks connected to the transport of the leachate; possibility of treating the percolate in a plant designed ad hoc for characteristics of the leachate, allowing also to close inside the landfill the cycle of stabilization and mineralization of trash; possibility of using biogas produced by the landfill for supplying energy to the leachate treatment plant.
In this way, constructed wetlands represent a viable choice, offering extremely positive characteristics for treatment of the landfill leachate, as: great efficiency in lowering organic matter due to the variety of microbic species normally present in these systems; good removal of heavy metals; great capacity of nitrifying-denitrifying, with consequent lowering of high concentrations of ammonia typical of landfill leachate; sensible reduction of the volume of the leachate, due to high evapotranspiration bring by plants, and consequently sensible reduction of the costs of an eventual further treatment of the leachate.
Moreover, the capacity of a phytodepuration system to create the natural habitat for animals and wildlife favours in a very significative way the environmental restoration of the area occupied by the landfill, both during its exercise and after its closing. All these aspects come together with typical advantages of constructed wetlands, like low costs of realization and management and very good removal efficiency.
The choice of these kinds of biotechnologies with low environmental impact is growing more and more at the international level; just for example, consider the international conference “Wetlands for treatment of landfill leachate” which took place in Michigan (USA) in 1997 and reported results of about 30 case studies of this plants (Constructed wetland for the treatment of landfill leachate – Lewis Publisher).
In the design constructed wetlands for the treatment of landfill leachate most utilized typologies of plant scheme are constituted of a storage basin (aerated ponds) in the head (with function of equalization of liquid flows, strongly connected to precipitations), submerged flow systems, often combination of horizontal and vertical flow systems, final finissage in free water surface systems (eventually in combination with horizontal submerged flow systems to enforce denitrifying). Treated wastewater is then stored and utilized for irrigation of green areas of the landfill or cultivated areas with plantation of highly evapotranspirative species, or is discharged in superficial water.