Heavy metal leaching and environmental risk from the use of compost-like output as an energy crop growth substrate

K Page,M.J Harbottle,P.J Cleall,T.R Hutchings

doi:10.1016/j.scitotenv.2014.04.021

K Page, M.J Harbottle + Show 2 more

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https://doi.org/10.1016/j.scitotenv.2014.04.021

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Abstract

Conversion of productive agricultural land towards growth of energy crops has become increasingly controversial. Closed landfill sites represent significant areas of brownfield land, which have potential for the establishment of energy crops. Increasingly composts are now being produced from the degradable fraction of mixed municipal solid waste (MSW) and are commonly referred to as Compost-Like-Output (CLO). However, leaching of heavy metal and other elements due to the use of CLO as soil amendment has the potential to pose a risk to the wider environment as a diffuse pollution source if not managed correctly. Salix viminalis and Eucalyptus nitens were grown at 5 different CLO application rates (equivalent to 250, 1000, 3000, 6000, 10000kgN/Ha) with weekly leachate analysis to assess the solubility of heavy metals and the potential release into the environment. The change in plant total dry mass suggested 3000kgN/Ha as the optimum application rate for both species. Weekly leachate analysis identified excess soluble ions within the first 4weeks, with heavy metals concentrations exceeding water quality limits at the higher application rates (>3000kgN/Ha). Heavy metal uptake and accumulation within each species was also investigated; S. viminalis accumulated greater levels of heavy metals than E. nitens with a general trend of metal accumulation in root>stem>leaf material. Heavy metal leaching from soils amended with CLO has the potential to occur at neutral and slightly alkaline pH levels as a result of the high buffering capacity of CLO. The use of CLO at application rates of greater than 250kgN/Ha may be limited to sites with leachate collection and containment systems, not solely for the heavy metal leaching but also excess nitrogen leaching. Alternatively lower application rates are required but will also limit biomass production.

Highlights

In the UK the amount of biodegradable waste reaching landfills must be reduced to 35% of the 1995 levels by 2020 under the EuropeanK
Salix viminalis and Eucalyptus nitens were grown at 5 different CLO application rates with weekly leachate analysis to assess the solubility of heavy metals and the potential release into the environment
This study investigates the effect of different application rates of CLO used for soil improvement on the leaching of soluble heavy metals and the risk to the wider environment when used as a nutrient source for two tree species Salix viminalis and Eucalyptus nitens

Summary

Introduction

In the UK the amount of biodegradable waste reaching landfills must be reduced to 35% of the 1995 levels by 2020 under the EuropeanK. The use of CLO is permitted on brownfield sites providing that an ecological benefit to the site can be demonstrated (Environment Agency, 2011). It has been suggested that CLO can be applied to landfill sites as a fertile soil amendment to aid the growth of Short Rotation Coppice (SRC) crops for use as a renewable biomass source (Bardos et al, 2007). Brownfield sites commonly have poor soil structure and low nutrient content which can be a significant barrier in the development of plant growth (Nixon et al, 2001). The addition of CLO to poor soils may improve the soil structure and provide sufficient nutrients for rapid growth of SRC species helping to alleviate potential nutrient limitations on crop yields (Forest Research, 2008). The effect on soil chemistry from the application of CLO and the impact on SRC biomass yields are largely unknown

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