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

Abstract

Since the introduction of an EC-directive on stronger demands on covering and lining of
landfills, 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 to
these stronger demands. Covering of landfills has traditionally been carried out with till
as 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 not
very 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 partly
covered with composted sewage sludge mixed with mineral soil, partly with ash. The aim
was to find out whether the leachate from the covered areas had to be subject for further
treatment before being discharged into the recipient. The leachate was analysed for
nitrogen and phosphorus. The results from the first three months of the experiment
showed high concentrations of both nitrogen and phosphorus in the leachate, probably
due to a washing effect. It is expected that the nutrient concentrations will decrease in the
future when the content of nutrients in the covering materials have been washed out and
when vegetation has been established. Further investigations of the leachate will confirm
this. Based on these findings and the fact that the materials fulfil other requirements for
covering materials, it was concluded that both sludges and ashes could be regarded as
suitable materials for a sustainable landfill covering. Further investigations on the subject
are however suggested.