The utilisation of a willow vegetation filter for the treatment of landfill leachate is an environmentally and economically appealing solution for landfill operators. Investigations into the design and efficacy of the system, the effects of landfill leachate irrigation on soil ecology, soil chemistry and willow growth were undertaken.
Two low cost, high density polyethylene-lined experimental willow plots (25x50 m2) were installed at Cranford landfill, Northamptonshire, UK, and irrigated with landfill leachate between June 2001 and October 2005. During the growing season, leachate volume was often reduced to zero. On other occasions, maximum removal efficiencies of between 33 % and 75 % for total Kjeldahl nitrogen, chemical oxygen demand and sodium, potassium and chloride ions were determined in landfill leachate effluent samples.
The addition of landfill leachate produced no negative effects on both soil and foliar macronutrients, which were found to be in the range for sufficient or optimum growth and where additional fertilisers would not bring about a further increase in yields. The effects of landfill leachate application on soil microbial communities were explored and were found to be significantly higher for dehydrogenase activity and ammonium oxidising bacteria in the plot receiving a higher rate of leachate application.
An economic analysis was carried out to demonstrate the financial viability of a willow vegetation filter as a treatment for landfill leachate. Willow vegetation filters could provide a desirable alternative to conventional treatment systems, such as sequencing batch reactors, as they incur lower capital expenses and potentially similar operational costs. This study also identified additional revenue benefits in the region of £94 per hectare for wood chip heat/energy production.
The results from the willow vegetation filter under investigation in this study demonstrated that this type of system can be effective, in terms of volume reduction and removal efficiency in landfill leachate, with no detrimental effect upon the trees or surrounding environment