Journal of Hazardous Materials 330 (2017) 29–35 Contents lists available at ScienceDirect Journal of Hazardous Materials journal homepage: www.elsevier.com/locate/jhazmat Multi-approach characterization of organic sediment produced by an anaerobic digestion plant fed with pig slurry and stored for a long term in a lagoon Anna Ricci a , Luisa Massaccesi b , Daniela Pezzolla a , Giuseppe Corti c , Alberto Agnelli b , Giovanni Gigliotti a,∗ a Department of Civil and Environmental Engineering, University of Perugia, Borgo XX Giugno, 74, 06124, Perugia, Italy b Department of Agricultural, Food and Environmental Sciences, University of Perugia, Borgo XX Giugno, 74, 06124, Perugia, Italy c Department of Agricultural, Food and Environmental Sciences, Polytechnic University of Marche, Via Brecce Bianche 10, 60131, Ancona, Italy h i g h l i g h t s • The aged organic sediment derived from pig slurry digestate is characterised by chemical and spectroscopic methods. • High concentrations of Cu, Zn, K and Na elements are found in the sediment. • Sediment is mainly made by recalcitrant organic matter as cellulose. • By spectroscopy speciation, the two main Zn forms are Zn phosphate and Zn sulfide. • In the sediment, most of the Zn and Cu are in very stable forms. a r t i c l e i n f o Article history: Received 19 July 2016 Received in revised form 2 February 2017 Accepted 4 February 2017 Available online 5 February 2017 Keywords: Anaerobic digestate XANES/XES spectroscopy Sequential extraction Zinc Copper a b s t r a c t This study combined different approaches to characterize organic sediments produced by an anaerobic digestion plant feed with pig slurry, and accumulated for many years in a lagoon. The results of all analyses identified a certain homogeneity of the sediments. As a consequence of the pig diet, the sediment contained an high concentration of Zn (about 4 g kg −1 ) and Cu (about 1.2 g kg −1 ), which were mostly associated to the particles with a size ranging from 2 to 53 m. The sediment was made of large amount of organic matter, mostly cellulose and recalcitrant molecules, and 30–40% mineral fraction. XANES and XES spectroscopies indicated the presence of zinc phosphate (38%), zinc sulfide (32%), zinc carbonate (19%), and zinc oxide (11%). The presence in the sediment of forms characterized by a very scarce solubility, as also confirmed by the Zn and Cu chemical speciation, indicated a low bioavailability of these metals. However, although their low mobility, the high concentrations of Zn and Cu allowed to consider the sediment not suitable to use as a fertiliser due to the potential risk of metal interaction with the food chain. © 2017 Elsevier B.V. All rights reserved. 1. Introduction The EU eco-sustainable policies and growing demand for energy have determined an interest to new forms of energy production, which can contribute to the replacing of fossil fuel. One of these forms is the biogas production from anaerobic digestion (AD) of ∗ Corresponding author. E-mail addresses: annaricci83@libero.it (A. Ricci), luisa.massaccesi@unipg.it (L. Massaccesi), daniela.pezzolla@unipg.it (D. Pezzolla), g.corti@univpm.it (G. Corti), alberto.agnelli@unipg.it (A. Agnelli), giovanni.gigliotti@unipg.it (G. Gigliotti). different feedstocks in plants, which differ for types and sizes. In 2014, 1681 biogas plants operated in Italy, defined the third EU country for the energy produced from biogas, after Germany and United Kingdom [1]. After the AD process, the organic matter (OM) of the digestate withstands some important modifications, mostly related to the increasing of low degradable organic compounds [2]. However, as metal concentration of the organic wastes feeding the plant is generally conserved at the end of the digestion process, so the addition of matrices like pig slurries, which are usually char- acterized by a high content of Zn and Cu, can contribute to the total amount of heavy metals in the digestate. Therefore, the agro- nomic use of pig slurries or their digestate [3,4] is paying attention http://dx.doi.org/10.1016/j.jhazmat.2017.02.003 0304-3894/© 2017 Elsevier B.V. All rights reserved.