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Energy analysis of sewage sludge energy conversion processes for Turkey—investigation of existing drying and combustion plants


Thermal energy content of sewage sludge offers opportunities in terms of energy production. Incineration is extensively used for energy conversion of sludge. Dewatered sludge needs to be dried prior to incineration or supplementary fuel should be supplied to the incinerator. Energy production rate is exaggerated when dryer energy is neglected. Net energy production rate depends on dryer energy consumption. The effect of the dryer energy consumption on the net energy production is not emphasized. Energy consumption data of the sludge management process is collected from wastewater management utilities. Thermal and electrical energy conversion of sludge is studied within a scenario analysis. Energy consumption of the examining drying plants (11000–3900 kJ/kg water) is higher than literature (4320–3000 kJ/kg water) data. In order for the dewatered sludge to be burned and dried with its own energy (90% solid), the ratio of its lower calorific value to the specific energy consumption of drying should be 2.8. Net energy production with fully dried sludge is only possible in Plant 4. In the case of auto-thermal combustion, with partially dried (50% solid) sludge, net energy production is possible in 3 of the 4 plants examined. Twenty-five to seventy-five percent of the energy consumption of the wastewater treatment plant can be met by electricity generated using biogas and sludge.

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Data availability

Not Applicable.



Dry matter


Electrical energy

Hevap :

Latent heat of water evaporation


Lower heating value


Municipal solid waste


Natural gas


Thermal energy


Specific energy consumption


Supplementary fuel


Sewage sludge


Volumetric flow rate


Wastewater treatment plant


Mass flow rate of sludge


Wet base

X in,DM :

Humidity of dewatered sludge

X out,DM :

Humidity of dried sludge

η conversion :

Electrical conversion efficiency

η thermal :

Thermal efficiency of incineration plant


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The authors would like to warmly thank the Water and Sewage Administration of Antalya (ASAT), Bursa (BUSKİ), İstanbul (İSKİ), and Kocaeli (İSU) Metropolitan Municipalities for their helpful cooperation and for providing the sludge treatment data.

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All authors contributed to the conceptualization of the research and writing the manuscript. All authors read and approved the final manuscript.

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Correspondence to Süleyman Sapmaz.

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Sapmaz, S., Kılıçaslan, İ. Energy analysis of sewage sludge energy conversion processes for Turkey—investigation of existing drying and combustion plants. Biomass Conv. Bioref. (2022).

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  • Combustion
  • Electricity generation
  • Energy efficiency
  • Industrial dryer
  • Sewage sludge