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

Andreas Nordin, Anna Strandberg, Sana Elbashir, Lars-Erik Åmand, Nils Skoglund and Anita Pettersson
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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

Energies, 2020, vol. 13, issue 7, 1-24

Abstract: 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.

Keywords: sewage sludge; grate boiler; heavy metals; phosphorus recovery; co-combustion (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2020
References: View references in EconPapers View complete reference list from CitEc
Citations: View citations in EconPapers (6)

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