Combined purification and reuse of landfill leachate by constructed wetland and irrigation of grass and willows

Landfill leachate is an important pollution factor resulting from municipal landfill sites. Due to low biodegradability, high nitrogen content and other possible toxic components of the leachate, the co-treatment of leachate on conventional municipal wastewater (WW) treatment plants is undesirable. Low-cost on-site treatment methods as well as possibilities of leachate reuse as a fertiliser for the growth of energy crops would present a solution to this problem. This article presents a combination of leachate pre-treatment in constructed wetland (CW) and subsequent reuse for the irrigation of the closed and vegetated part of the landfill site. Pre-treatment of leachate in CW contributed to the reduction of nutrients and the retention of water peaks. Although the pre-treated leachate still contained high concentrations of several pollutants and nutrients, irrigation of vegetated landfill cover with high leachate input (400 m3 per month per hectare in average) did not result in excessive accumulation of salts, heavy metals, or nutrients, which could negatively affect soil properties and plant growth. Because of an additional input of water and nutrients from leachate, the growth of plants on the irrigated landfill cover was better compared to the surrounding vegetation; this indicates that the vegetated landfill cover contributed to an additional removal of excess leachate volume and leachate components from the system.

Pre-treatment of leachate in CW contributed to the reduction of nutrients and the retention of water peaks. Irrigation of vegetated landfill cover has so far not shown any excessive accumulation of salts, heavy metals or nutrients, which could negatively affect soil properties and plant growth in spite of irrigation with leachate containing high concentration of parameters. However, further regular monitoring of soil and plant material is carried on to prevent long-term soil quality degradation or plant damage. The cover vegetation grew rapidly and showed higher indices as compared to surrounding vegetation. The results showed that under controlled conditions (sufficient amount of precipitation – approximately 1000 mm per year, low heavy metal concentrations), leachate acts as a good fertiliser for landfill vegetative cover. Uptake of nutrients from leachate by plants (S. purpurea, grasses) probably presented a small portion of the leachate mass load during the observation period when part of the landfill site was still under the operation. To achieve higher nutrient uptake, a larger irrigated surface and tree species with higher biomass production, such as fast growing clones of Salix viminalis in short rotation ˇic coppices used as energy crops, would be needed. The final picture of the functioning of the whole system will be seen after the closure and revegetation of the entire landfill site.