Energy Recovery from Sewage Sludge: The Case Study of Croatia

Dinko Đurđević, Paolo Blecich and Željko Jurić
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Dinko Đurđević: Energy Institute Hrvoje Požar, 10000 Zagreb, Croatia
Paolo Blecich: Faculty of Engineering, University of Rijeka, 51000 Rijeka, Croatia
Željko Jurić: Energy Institute Hrvoje Požar, 10000 Zagreb, Croatia

Energies, 2019, vol. 12, issue 10, 1-19

Abstract: Croatia produced 21,366 tonnes of dry matter (DM) sewage sludge (SS) in 2016, a quantity expected to surpass 100,000 tonnes DM by 2024. Annual production rates for future wastewater treatment plants (WWTP) in Croatia are estimated at 5.8–7.3 Nm 3 /people equivalent (PE) for biogas and 20–25 kg DM /PE of sewage sludge. Biogas can be converted into 12–16 kWh el /PE of electricity and 19–24 kWh th /PE of heat, which is sufficient for 30–40% of electrical and 80–100% of thermal autonomy. The WWTP autonomy can be increased using energy recovery from sewage sludge incineration by 60% for electricity and 100% of thermal energy (10–13 kWh el /PE and 30–38 kWh th /PE). However, energy for sewage sludge drying exceeds energy recovery, unless solar drying is performed. The annual solar drying potential is estimated between 450–750 kg DM /m 2 of solar drying surface. The lower heating value of dried sewage sludge is 2–3 kWh/kg DM and this energy can be used for assisting sludge drying or for energy generation and supply to WWTPs. Sewage sludge can be considered a renewable energy source and its incineration generates substantially lower greenhouse gases emissions than energy generation from fossil fuels. For the same amount of energy, sewage sludge emits 58% fewer emissions than natural gas and 80% less than hard coal and fuel oil. Moreover, this paper analysed the feasibility of sludge disposal practices by analysing three scenarios (landfilling, co-incineration, and mono-incineration). The analysis revealed that the most cost-effective sewage sludge disposal method is landfilling for 60% and co-incineration for 40% of the observed WWTPs in Croatia. The lowest CO 2 emissions are obtained with landfilling and mono-incineration in 53% and 38% of the cases, respectively.

Keywords: wastewater treatment; sewage sludge; solar drying; energy recovery; incineration (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: 2019
References: View references in EconPapers View complete reference list from CitEc
Citations: View citations in EconPapers (23)

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