Journal of Hazardous Materials 161 (2009) 1003–1009 Contents lists available at ScienceDirect Journal of Hazardous Materials journal homepage: www.elsevier.com/locate/jhazmat Electroremediation of straw and co-combustion ash under acidic conditions A.T. Lima a,∗ , L.M. Ottosen b , A.B. Ribeiro a a Department of Sciences and Environmental Engineering, Faculty of Sciences and Technology, New University of Lisbon, 2829-516 Caparica, Portugal b Department of Civil Engineering, Building 118, Technical University of Denmark, DK-2800 Lyngby, Denmark article info Article history: Received 28 June 2007 Received in revised form 17 February 2008 Accepted 14 April 2008 Available online 22 April 2008 Keywords: Electrodialysis Biomass Fly ash Cadmium Chromium abstract Biomass, such as wood and straw, is currently used in EU as a renewable energy source for energy production and this application is expected to rise in coming years. Combined heat and power instal- lations produce fly ash, which is considered hazardous waste. The fly ash management issue should be addressed before biomass combustion is considered a truly sustainable technology. The electrodialytic process is a remediation technique able to assist the management of fly ash. For this work, straw and co-combustion of wood ash are briefly characterized and their electrodialytic treatment is carried out under acidic conditions. Straw ashes presented high removal rates for Ca, Cu, Cr and particularly for Cd, which has been reduced to a level bellow the established by Danish regulations. Acidification also induced a high dissolution and a lower pH of the ash. Fly ash from co-combustion of wood presents similarities with wood ash alone. However, further characterization should be carried out before any comparison regarding applicable legislation. Under acidic conditions, the electrodialytic treatment was not effective for the co-combustion wood ash. The heavy metals appeared in the least soluble fraction of this ash and lowering the pH of such an alkaline material does not mean sustainability and may hinder its reuse. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Biomass, such as wood, straw and energy crops, is an impor- tant renewable and CO 2 neutral energy source in Europe. Biomass resources are closely linked to EU energy policy, where decreases in CO 2 emission are considered necessary and the use of renewable sources for the production of energy plays an important role. The White Paper on Renewable Energy sets the EU quantitative targets for renewable energy until 2010 in 12% of the total energy pro- duction. In 2005, according to the European Commission dossier on biomass [1], 4% of the energy outcome in EU was from wood (3%) and straw (1%) combustion. There is an overall pressure on renewable energy sources, where combustion of biomass repre- sents an important resource for the combined heat and power (CHP) production. CHP installations are high technology plants where incineration of biomass and fossil may be combined or combusted alone. As incinerators, the remaining fractions of the process pos- sess an intrinsic hazardousness, especially fly ash. According to the guidelines from the Danish Environmental Protection Agency [2], bottom ashes from straw and wood combustion will in most cases meet the demands for category H3 and T3, respectively. This ∗ Corresponding author. Tel.: +351 212948553; fax: +351 212948551. E-mail addresses: atlima@fct.unl.pt, lima.at@gmail.com (A.T. Lima). enables direct use of bottom ash from biomass combustion on agricultural fields [3]. Nevertheless, the fly ashes from biomass combustion usually present Cd concentrations that may exceed the top category, H1 and T1, which implicates ash deposition in landfill [4]. Therefore, limitations of deposition of fly ash have been established in 5 mg Cd kg -1 for straw ash and 15 mg Cd kg -1 for wood ash, both in the disposal of 500 kg of ash as fertilizer in the soil with the restriction of 5 years interval [2,4,5]. Besides their eventual hazardousness, these fly ashes have a fertilizing value relying on its K, Mg and P content [4,6], where removal of heavy metals could enable the (re)application of Danish regula- tions. Since bio ashes do not present the toxicity level of other fly ashes (e.g. resulting from municipal solid waste incineration) [7], reutilization could be a sustainable management option for these residues after the removal of heavy metals. The electrodialytic pro- cess (EDR) is a remediation technique first described for heavy metal contaminated soil [8]. The method combines an electric DC field as cleaning agent with the use of ion-exchange mem- branes, allowing the regulation of ion fluxes in a cell arrangement first developed at the Technical University of Denmark. Details can be found elsewhere, e.g. [9,10]. The EDR has been successfully applied for the removal of Cd in straw ash [5,6] and Peder- sen [4] and Pedersen et al. [11] studied its application to wood ash. 0304-3894/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2008.04.046