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Wednesday, 30 May 2007

Composted Green Waste


 Christopher N. Lowe, Kevin R. Butt and Thomas Ormerod

School of Natural Resource, University of Central Lancashire, Preston, PR1 2HE, UK

Large-scale green waste processing facilities are now common-place on landfill sites throughout the UK. The product, composted green waste (CGW), has commercial value as a soil conditioner, but surplus, lower quality material may also be used on site as additional daily cover. A more environmentally sensitive and cost effective use for the latter is incorporation into landfill cap to improve soil quality. A proven method of incorporating organic matter into soils is through the action of earthworms. The role of earthworms in the process of soil formation and maintenance of soil fertility is widely recognised and has led to their inoculation into degraded land to enhance soil restoration. However, development of sustainable populations is often limited by a deficit of organic matter. Therefore earthworm inoculation allied to CGW application may be considered as an effective route towards final restoration of a site.

This study was conducted at two landfill sites in the UK (Calvert and Clifton Marsh). At both sites, waste filled cells had been capped with (1-2 m) compacted clay (engineering cap). At Calvert this engineering cap was covered with a layer of less compacted clay but at Clifton Marsh a layer of soil / subsoil mixed with CGW was applied. At Calvert (1999), a range of surface application and mechanical incorporation treatments of CGW were established in 50 m2 plots where earthworms had been introduced 7 years earlier. Monitoring showed that surface application of CGW promoted earthworm numbers and biomass. In 2003, 3 species of earthworms (Apporectodea caliginosa, Apporectodea longa and Octolasion cyaneum) were inoculated into 400 m2 plots with a treatment of surface applied CGW versus control. Results indicated that addition of CGW increased earthworm survival and enhanced cap integrity. At Clifton Marsh (2005), earthworm populations were monitored from sites representing a chronosequence (1.5, 3.5 and 5.5 years after capping) and in undisturbed pasture (control) adjacent to the Landfill site. Natural colonisation was rapid with earthworm number and biomass in the 5.5 yr cap comparable with the control. Species number (4-6) was consistent across the 4 sites but community composition varied with location and was attributed to specific ecological requirements. Percentage of mature worms was inversely related to age of cap with 85, 52 and 23 % mature in the 1.5, 3.5 and 5.5 yr old sites respectively compared with 24 % in the control.

Results indicate that at sites lacking topsoil, surface application of CGW coupled with earthworm inoculation is an alternative and sustainable method of land restoration. In addition, incorporation of CGW into landfill capping material can promote the development of earthworm populations and increase site amelioration.


Last Updated ( Thursday, 31 May 2007 )
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