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Co-Combustion of Municipal Sewage Sludge and Biomass in a Grate Fired Boiler for Phosphorus Recovery in Bottom Ash


  • Andreas Nordin

    (Swedish Centre for Resource Recovery, University of Borås, SE-501 90 Borås, Sweden)

  • Anna Strandberg

    (Department of Applied Physics and Electronics, Umeå University, SE-901 87 Umeå, Sweden)

  • Sana Elbashir

    (Swedish Centre for Resource Recovery, University of Borås, SE-501 90 Borås, Sweden)

  • Lars-Erik Åmand

    (Swedish Centre for Resource Recovery, University of Borås, SE-501 90 Borås, Sweden)

  • Nils Skoglund

    (Department of Applied Physics and Electronics, Umeå University, SE-901 87 Umeå, Sweden)

  • Anita Pettersson

    (Swedish Centre for Resource Recovery, University of Borås, SE-501 90 Borås, Sweden)


Phosphorus has been identified as a critical element by the European Union and recycling efforts are increasingly common. An important phosphorus-containing waste stream for recycling is municipal sewage sludge (MSS), which is used directly as fertilizer to farmland. However, it contains pollutants such as heavy metals, pharmaceutical residues, polychlorinated bi-phenyls (PCBs) and nano-plastics. The interest in combustion of MSS is continuously growing, as it both reduces the volume as well as destroys the organic materials and could separate certain heavy metals from the produced ashes. This results in ashes with a potential for either direct use as fertilizer or as a suitable feedstock for upgrading processes. The aim of this study was to investigate co-combustion of MSS and biomass to create a phosphorus-rich bottom ash with a low heavy metal content. A laboratory-scale fixed-bed reactor in addition to an 8 MWth grate-boiler was used for the experimental work. The concentration of phosphorus and selected heavy metals in the bottom ashes were compared to European Union regulation on fertilizers, ash application to Swedish forests and Swedish regulations on sewage sludge application to farmland. Element concentrations were determined by ICP-AES complemented by analysis of spatial distribution with SEM-EDS and XRD analysis to determine crystalline compounds. The results show that most of the phosphorus was retained in the bottom ash, corresponding to 9–16 wt.% P 2 O 5 , while the concentration of cadmium, mercury, lead and zinc was below the limits of the regulations. However, copper, chromium and nickel concentrations exceeded these standards.

Suggested Citation

  • Andreas Nordin & Anna Strandberg & Sana Elbashir & Lars-Erik Åmand & Nils Skoglund & Anita Pettersson, 2020. "Co-Combustion of Municipal Sewage Sludge and Biomass in a Grate Fired Boiler for Phosphorus Recovery in Bottom Ash," Energies, MDPI, vol. 13(7), pages 1-24, April.
  • Handle: RePEc:gam:jeners:v:13:y:2020:i:7:p:1708-:d:341274

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    References listed on IDEAS

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    Cited by:

    1. Marzena Smol & Christian Adam & Stefan Anton Kugler, 2020. "Thermochemical Treatment of Sewage Sludge Ash (SSA)—Potential and Perspective in Poland," Energies, MDPI, vol. 13(20), pages 1-17, October.
    2. Coskun, Can & Oktay, Zuhal & Koksal, Tunc & Birecikli, Bahadır, 2020. "Co-combustion of municipal dewatered sewage sludge and natural gas in an actual power plant," Energy, Elsevier, vol. 211(C).
    3. Naeimeh Vali & Lars-Erik Åmand & Aurélie Combres & Tobias Richards & Anita Pettersson, 2021. "Pyrolysis of Municipal Sewage Sludge to Investigate Char and Phosphorous Yield together with Heavy-Metal Removal—Experimental and by Thermodynamic Calculations," Energies, MDPI, vol. 14(5), pages 1-18, March.
    4. Izabella Maj & Sylwester Kalisz & Szymon Ciukaj, 2022. "Properties of Animal-Origin Ash—A Valuable Material for Circular Economy," Energies, MDPI, vol. 15(4), pages 1-15, February.

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