Limitations for heavy metal release during thermo-chemical treatment of sewage sludge ash

Journal Article · Wed Jun 15 00:00:00 EDT 2011 · Waste Management

DOI:https://doi.org/10.1016/j.wasman.2011.01.029· OSTI ID:21550376

Nowak, Benedikt ^[1]; Perutka, Libor ^[1]; Aschenbrenner, Philipp ^[2]; Kraus, Petra ^[3]; Rechberger, Helmut ^[2]; Winter, Franz ^[1]

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1. Institute of Chemical Engineering, Vienna University of Technology, Getreidemarkt 9/166, A-1060 Vienna (Austria)
2. Institute for Water Quality, Resource and Waste Management, Vienna University of Technology, Karlsplatz 13/226, A-1040 Vienna (Austria)
3. ASH DEC Umwelt AG, Donaufelderstrasse 101/4/5, A-1210 Vienna (Austria)

Phosphate recycling from sewage sludge can be achieved by heavy metal removal from sewage sludge ash (SSA) producing a fertilizer product: mixing SSA with chloride and treating this mixture (eventually after granulation) in a rotary kiln at 1000 {+-} 100 deg. C leads to the formation of volatile heavy metal compounds that evaporate and to P-phases with high bio-availability. Due to economical and ecological reasons, it is necessary to reduce the energy consumption of this technology. Generally, fluidized bed reactors are characterized by high heat and mass transfer and thus promise the saving of energy. Therefore, a rotary reactor and a fluidized bed reactor (both laboratory-scale and operated in batch mode) are used for the treatment of granulates containing SSA and CaCl{sub 2}. Treatment temperature, residence time and - in case of the fluidized bed reactor - superficial velocity are varied between 800 and 900 deg. C, 10 and 30 min and 3.4 and 4.6 m s{sup -1}. Cd and Pb can be removed well (>95 %) in all experiments. Cu removal ranges from 25% to 84%, for Zn 75-90% are realized. The amount of heavy metals removed increases with increasing temperature and residence time which is most pronounced for Cu. In the pellet, three major reactions occur: formation of HCl and Cl{sub 2} from CaCl{sub 2}; diffusion and reaction of these gases with heavy metal compounds; side reactions from heavy metal compounds with matrix material. Although, heat and mass transfer are higher in the fluidized bed reactor, Pb and Zn removal is slightly better in the rotary reactor. This is due the accelerated migration of formed HCl and Cl{sub 2} out of the pellets into the reactor atmosphere. Cu is apparently limited by the diffusion of its chloride thus the removal is higher in the fluidized bed unit.

• OSTI ID: 21550376
• Journal Information: Waste Management, Vol. 31, Issue 6; Other Information: DOI: 10.1016/j.wasman.2011.01.029; PII: S0956-053X(11)00062-6; Copyright (c) 2011 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; ISSN 0956-053X
• Country of Publication: United States
• Language: English

Related Subjects

12 MANAGEMENT OF RADIOACTIVE WASTES, AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES
ASHES
BIOLOGICAL AVAILABILITY
CALCIUM CHLORIDES
DIFFUSION
ENERGY CONSUMPTION
FERTILIZERS
FLUIDIZED BED REACTORS
FLUIDIZED BEDS
GRANULATION
HEAT TRANSFER
HEAVY METALS
HYDROCHLORIC ACID
KILNS
MASS TRANSFER
MATRIX MATERIALS
PHOSPHATES
RECYCLING
SEWAGE SLUDGE
VOLATILITY
ALKALINE EARTH METAL COMPOUNDS
BIOLOGICAL MATERIALS
BIOLOGICAL WASTES
CALCIUM COMPOUNDS
CALCIUM HALIDES
CHLORIDES
CHLORINE COMPOUNDS
COMBUSTION PRODUCTS
ELEMENTS
ENERGY TRANSFER
FABRICATION
FUEL DISPERSION REACTORS
HALIDES
HALOGEN COMPOUNDS
HOMOGENEOUS REACTORS
HYDROGEN COMPOUNDS
INORGANIC ACIDS
INORGANIC COMPOUNDS
MATERIALS
METALS
OXYGEN COMPOUNDS
PHOSPHORUS COMPOUNDS
REACTORS
RESIDUES
SEWAGE
SLUDGES
WASTES