Distribution of ash forming elements during pyrolysis of municipal wastewater sludge and sludge from milk processing factories

• In the long term, there is a need for alternative methods to recover energy and nutrients from increasing volumes of sludge generated from wastewater treatment plants. Pyrolysis can be an interesting option, which can reduce health and environmental risks, while providing an avenue for the recovery of energy and nutrients. One of the main concerns related to thermal conversion technologies is the release and fate of heavy metals and contaminants existing in the feedstock. Therefore, a detailed understanding of the transformation pathways of problematic compounds is necessary to assess the suitability of pyrolysis. In this study pyrolysis of dried dairy sludge and sewage sludge was carried out using a simple laboratory fixed bed reactor. Characterisation of the feedstock and pyrolysis products was performed through proximate and ultimate analysis and the content of major and minor ash forming elements were determined. The mass balance information obtained from the experimental tests was used for an indicative distribution of Al, Ca, Fe, K, Mg, Na, P, S, Si, As, Ba, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, Sb, Se, Ti, V and Zn between solid and liquid pyrolysis products. Results indicate that distribution of major elements between pyrolysis products was similar for dairy sludge and sewage sludge, with Ca, Mg, Fe, P, Si, Al, Na and K predominantly retained in pyrolysis chars (pyrogenic solids). However, substantial quantities of Al, K, Na and Si were detected in pyrolysis oil and in the aqueous fraction. The heavy metals and trace elements were mainly retained in the pyrolysis chars (pyrogenic solids) with the exception of As, Ba, Cd, Se, Sb and Pb, which were also detected in the liquid products.

Ämnesord

LANTBRUKSVETENSKAPER  -- Husdjursvetenskap -- Husdjursvetenskap (hsv//swe)

AGRICULTURAL SCIENCES  -- Animal and Dairy Sience -- Animal and Dairy Science. (hsv//eng)

TEKNIK OCH TEKNOLOGIER  -- Kemiteknik -- Kemiska processer (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Chemical Engineering -- Chemical Process Engineering (hsv//eng)

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