Heavy metal content in ash of energy crops growing in sewage-contaminated natural wetlands: Potential applications in agriculture and forestry?

One of the greatest current challenges is to find cost-effective and eco-friendly solutions to the ever increasingneeds of modern society. Some plant species are suitable for a multitude of biotechnological applications suchas bioenergy production and phytoremediation. A sustainable practice is to use energy crops to clean up pollutedlands or to treatwastewater in constructed wetlands without claiming further arable land for biofuel production.However, the disposal of combustion by-products may add significant costs to the whole process, especiallywhen it deals with toxic waste. This study aimed to investigate the possibility of recycling ash from energy biomassas a fertilizer for agriculture and forestry. In particular, the concentrations of Cd, Cr, Cu,Mn, Pb and Znwereanalyzed in the plant tissues and corresponding ash of the grasses Phragmites australis and Arundo donax, collectedin an urban stream affected by domestic sewage. Results showed that the metal concentration in ash is 1.5–3times as high as the values in plant tissues. However, metal enriched ash showed much lower element concentrationsthan the legal limits for ash reutilization in agriculture and forestry. This study found that biomass ashfrom constructed wetlands may be considered as a potential fertilizer rather than hazardous waste. Energy frombiomass can be a really sustainable and clean option not only through the reduction of greenhouse gas emissions,but also through ash recycling for beneficial purposes, thus minimizing the negative impacts of disposal.© 2013 Elsevier B.V. All rights reserved.