Environmental impacts of landfill covering by use of industrial by-products

Since the introduction of an EC-directive on stronger demands on covering and lining oflandfills, the Swedish Parliament has adopted new legislation on waste deposition.Within a near future, a large number of landfills in Sweden have to be closed down due tothese stronger demands. Covering of landfills has traditionally been carried out with tillas covering material. The use of till causes depletion of a natural resource and in addition,high costs for transportation might arise. Alternative materials have thus been sought for.Two potential materials are sludge and ash. Their behaviour with regard to leaching is notvery well known and the focus of this work is to further investigate this issue. A pilotscale area on a closed-down part of the Gryta landfill site in Viistenis, Sweden; was partlycovered with composted sewage sludge mixed with mineral soil, partly with ash. The aimwas to find out whether the leachate from the covered areas had to be subject for furthertreatment before being discharged into the recipient. The leachate was analysed fornitrogen and phosphorus. The results from the first three months of the experimentshowed high concentrations of both nitrogen and phosphorus in the leachate, probablydue to a washing effect. It is expected that the nutrient concentrations will decrease in thefuture when the content of nutrients in the covering materials have been washed out andwhen vegetation has been established. Further investigations of the leachate will confirmthis. Based on these findings and the fact that the materials fulfil other requirements forcovering materials, it was concluded that both sludges and ashes could be regarded assuitable materials for a sustainable landfill covering. Further investigations on the subjectare however suggested.