Abstract—The highest extractable concentration in the artificial sweat fluid was observed for Ba (120mg/kg; d.w.). The highest extractable concentration in the artificial gastric fluid was observed for Al (9030mg/kg; d.w.). Furthermore, the extractable concentrations of Ba (550mg/kg; d.w.) and Zn (400mg/kg: d.w.) in the bottom ash using artificial gastric fluid were elevated. The extractable concentrations of all heavy metals in the artificial gastric fluid were higher than those in the artificial sweat fluid. These results are reasonable in the light of the fact that the pH of the artificial gastric fluid was extremely acidic both before (pH 1.54) and after (pH 1.94) extraction, whereas the pH of the artificial sweat fluid was slightly alkaline before (pH 6.50) and after extraction (pH 8.51). Keywords—Ash, artificial fluid, heavy metals, in vitro, waste. I. INTRODUCTION OMBUSTION via a bubbling fluidized bed (BFB) boiler is a widely used technology for energy recovery in the modern pulp and paper industry worldwide. The BFB boiler is especially suitable for inhomogeneous fuels. Fluidized bed combustion technology enables the co-combustion of various fuels even fuels with high moisture contents. Although the incineration of pulp and paper mill residues using fluidized bed combustion is rapidly becoming the ultimate solution for the final disposal of organic wastes, one disadvantage of energy generation from biomass is that it produces a considerable amount of ash residue. Ash residue fractions such as bottom ash, which accumulates at the bottom of the fluidized bed boiler, and fly ash, which is collected from the flue gas by methods such as electrostatic precipitation, wet scrubbing, fabric filters, or a mechanical device such as a multicyclone or a baghouse, constitute a major fraction of the solid residues produced by the power plants of pulp and paper mills. In vitro extraction tests [1] involving synthetic sweat, synthetic gastric/gastrointestinal and synthetic saliva fluids, are widely used for testing of metal release from consumer products such as textile [2] and artificial (polyethylene) turf Risto Pöykiö (PhD) is with the city of Kemi, FI-94100 Kemi, Finland (corresponding author; phone: +358-16-259 673; fax: +358-16-259 481; e- mail: risto.poykio@kemi.fi). Olli Dahl (Prof.) is with the Aalto University, School of Chemical Technology, Department of Forest Products Technology, P.O.Box 16300, Aalto FI-00076, Finland (e-mail: olli.dahl@aalto.fi). Hannu Nurmesniemi (PhD) is with the Stora Enso Oyj Veitsiluoto Mill, FI-94800 Kemi, Finland (e-mail: hannu.nurmesniemi@storaenso.com). [3] materials, and from items used in an every-day life such as coins or jewellery [4]. Furthermore, synthetic urine-like liquors are applied for studying the solubility of urinary calculi formation in clinic studies [5]. Synthetic human body fluids such as sweat and gastric/gastrointestinal and saliva fluids are also used as extractants to predict the availability of metals for human absorption in a range of industrial wastes such as coal fly ash [6], contaminated soil around old mining area [7] and of municipal solid waste such as compost [8]. Compared to the real human body fluids, which are in vivo tests, synthetic fluids are both rapid and inexpensive, requiring only a day to conduct and costing only a small fraction of what in vivo tests would cost. Although in vitro test by synthetic fluids have reported to have limitations, e.g. due to the fact that they cannot contain all the constituents of human fluids (e.g. proteins, enzymes, etc.), they provide an appropriate mean to determine the bioaccessibility of heavy metals in various materials. Although the real human body fluids have also been applied to study the solubility of heavy metals [9], [10], the application of synthetic body fluids promotes also the fact that real human body fluids may be unhygienic. Furthermore, the real human body fluids have reported to have an unstable nature [11], [12], and in the European Union (EU), their use is strictly regulated by the rules of national ethical committees. II. EXPERIMENTAL A. Bottom Ash Sampling Procedure The bottom ash investigated in this study originated from a large-sized (115 MW) bubbling fluidized bed (BFB) boiler at the power plant of a pulp and board mill complex located in Finland [13]. Sampling of a bottom ash was carried out over a period of three days, and individual sub-samples (1kg per sampling day) were collected and combined to give one composite sample with a weight of 3kg for the bottom ash. The sampling period represented normal process operating conditions for the combustion plant e.g. in terms of O 2 content and temperature. The incineration temperature in a bubbling fluidized bed boiler is ca. 800°C. During the sampling period when bottom ash was sampled from the outlet of the boiler, approximately 97% of energy produced by the BFB boiler originated from the incineration of clean forest residues (i.e. bark, woodchips, and sawdust), and 3% from the incineration of sludge from the primary clarifier of a wastewater treatment Extractable Heavy Metal Concentrations in Bottom Ash from Incineration of Wood-Based Residues in a BFB Boiler Using Artificial Sweat and Gastric Fluids Risto Pöykiö, Olli Dahl, Hannu Nurmesniemi C World Academy of Science, Engineering and Technology International Journal of Biomedical and Biological Engineering Vol:6, No:7, 2012 354 International Scholarly and Scientific Research & Innovation 6(7) 2012 scholar.waset.org/1307-6892/16913 International Science Index, Biomedical and Biological Engineering Vol:6, No:7, 2012 waset.org/Publication/16913