Browsing by Author "Merta, Elina"

Now showing 1 - 2 of 2

Carbon footprint of Finnish wastewater treatment plants
(2021-01-25) Awaitey, Alexis
Insinööritieteiden korkeakoulu | Master's thesis
Waste and wastewater treatment currently constitute approximately five percent of global greenhouse gas (GHG) emissions. Mitigating nation-wide GHG emissions requires collaboration between municipalities in reducing their carbon footprints. Since wastewater treatment plants (WWTPs) are essential municipal infrastructure, knowledge of their GHG emissions is important for assessing part of the total carbon footprint of municipalities. The aim of this thesis was to evaluate the carbon footprint of four WWTPs in Finland and provide recommendations for the sites in this study to reduce their GHG emissions. The processes included in the carbon footprint boundary were the treatment of wastewater, treatment of sludge and screenings, transport of chemicals, transport of screenings and sludge, as well as the energy and chemical consumption of the plant. The emissions from the wastewater network and disposal of sludge were excluded from the boundaries in this study. Carbon footprint results ranged from 45 – 82 kg CO2eq PE-1 year-1. Total emissions were dominated by fugitive emissions from wastewater and sludge treatment, with an average of 72 % of total carbon dioxide equivalent emissions (CO2eq). Energy consumption emissions were the second highest with an average of 19 %, followed by chemical consumption emissions with 7 % of total CO2eq emissions. Transport emissions constituted a minor share of 1 % of total CO2eq emissions. N2O emissions from wastewater treatment constituted an average of 59 % of total GHG emissions. Due to the high global warming potential of N2O, results showed high sensitivity of the carbon footprint to the N2O emission factor used. Based on the results, it was concluded that WWTPs with higher energy efficiencies or low indirect emissions would have higher shares and sensitivities to N2O emission factors. Due to the high share of direct emissions (particularly N2O), it is recommended that WWTPs in Finland evaluating their carbon footprint should invest in on-site measurement campaigns of fugitive N2O emissions of at least one year. This would reduce the under/overestimation of on-site emissions. In addition, it is also recommended that WWTPs monitor process-specific electricity consumptions which would help them identify energy-intensive processes on-site.
Comprehensive evaluation of the carbon footprint components of wastewater treatment plants located in the Baltic Sea region
(2022-02-01) Maktabifard, Mojtaba; Awaitey, Alexis; Merta, Elina; Haimi, Henri; Zaborowska, Ewa; Mikola, Anna; Mąkinia, Jacek
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Finland and Poland share similar environmental interests with regard to their wastewater effluents eventually being discharged to the Baltic Sea. However, differences in the influent wastewater characteristics, treatment processes, operational conditions, and carbon intensities of energy mixes in both countries make these two countries interesting for carbon footprint (CF) comparison. This study aimed at proposing a functional unit (FU) which enables a comprehensive comparison of wastewater treatment plants (WWTPs) in terms of their CF. Direct emissions had the highest contribution (70%) to the total CF. Energy consumption dominated the total indirect emissions in both countries by over 30%. Polish WWTPs benefitted more from energy self-sufficiency than Finnish plants as a result of higher electricity emission factors in Poland. The main difference between indirect emissions of both countries were attributed to higher chemical consumption of the Finnish WWTPs. Total pollution equivalent removed (TPErem) FU proposed enabled a better comparison of WWTPs located in different countries in terms of their total CF. High correlations of TPErem with other FUs were found since TPErem could balance out the differences in the removal efficiencies of various pollutants. Offsetting CF was found a proper strategy for the studied WWTPs to move towards low-carbon operation. The studied WWTPs could reduce their CF from up to 27% by different practices, such as selling biofuel, electricity and fertilizers. These findings are applicable widely since the selected WWTPs represent the typical treatment solutions in Poland, Finland and in the Baltic Sea region.