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 Nm3/people equivalent (PE) for biogas and 20–25 kgDM/PE of sewage sludge. Biogas can be converted into 12–16 kWhel/PE of electricity and 19–24 kWhth/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 kWhel/PE and 30–38 kWhth/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 kgDM/m2 of solar drying surface. The lower heating value of dried sewage sludge is 2–3 kWh/kgDM 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 CO2 emissions are obtained with landfilling and mono-incineration in 53% and 38% of the cases, respectively.
Making organizations aware of their carbon footprint (CF) and proposing measures to reduce it are important segments of climate change mitigation. As a part of this process, an enhanced Bilan Carbone model with incorporated country-specific greenhouse gas (GHG) emission factors was applied for CF calculations of three organizations (Agency, Faculty, and Institute). The model, fully in line with international CF calculation standards, can be applied to calculate the CF of any organization on the global level. The paper provides a comparative assessment of CFs of considered organizations and preconditions for a reliable comparison. The calculated CFs values for 2017 were 513.4 t CO2 e for the Agency, 4254.7 t CO2 e for the Faculty, and 477.0 t CO2 e for the Institute. Comparing specific CF, the Faculty had the highest value per employee (9.4 t CO2 e/employee) and the lowest value per heated area (131 kg CO2 e/m2), followed by the Institute (5.4 t CO2 e/employee and 222 kg CO2 e/m2) and the Agency (4.5 t CO2 e/employee and 294 kg CO2 e/m2). Using the enhanced Bilan Carbone model, adapted to national conditions, could lead to the harmonization of the organizations’ CF calculation and enable the identification of significant emission sources. This will facilitate the definition of GHG reduction targets and the identification of mitigation measures for achieving the targets, as presented in the example of the Institute.
The effects of climate change on Earth already exist in different forms -as an increase in global average temperatures, as a sea level rise or as extreme weather events, and it is necessary to take significant measures to mitigate and adapt to the climate change. One of the tools that can help in attempts to mitigate climate change is the use of carbon footprint concept, as a measure of the greenhouse gas emissions. Since there are different approaches, it is necessary and possible to establish a harmonised approach for calculating the organisations' carbon footprint, in order to obtain comparable results and benchmarks for different kinds of organisations. The Croatian version of the Bilan Carbone model, fully in accordance with appropriate international standards, with country-specific emission factors database, was tested on the case of the Energy Institute Hrvoje Požar for the period 2015-2017. The carbon footprint for 2017 was 650.6 tonnes or 7.31 tonnes per employee of carbon dioxide equivalent emissions, with dominant shares of people transport (59%) and energy sources (22%). This harmonised approach for carbon footprint calculation will lead to comparable results for the same kinds or groups of organisations and therewith, lighten the process of establishing the carbon footprint mitigation strategies.
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