Life cycle assessment of a biogas plant treating sewage sludge
Tran, Duy Anh (2024)
2024
Master's Programme in Environmental Engineering
Tekniikan ja luonnontieteiden tiedekunta - Faculty of Engineering and Natural Sciences
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Hyväksymispäivämäärä
2024-04-09
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tuni-202403293206
https://urn.fi/URN:NBN:fi:tuni-202403293206
Tiivistelmä
Sewage sludge treatment is a crucial part of keeping the city and environment clean, however, the process itself is also a significant contributor of environmental impact to every compartment of nature. As technology advances, it is necessary to adapt and change to enhance treatment efficiency and lower the impact.
This study quantified and compared the two operation layouts of a biogas plant in Finland, to see how the transition from old to new technology affect the performance in environmental aspect. The research was done through simulation with input based on the mass flow of the biogas plant.
The life cycle assessment model was built to compare the environmental footprints of the two layouts. It was found out that the more modern technology produced more emission equivalent by 1 to 8%, due to the chosen boundary, lack of proper input data, and efficiency value. Carbon dioxide equivalent was 3.89 x 10^6 for the original layout, and 4 x 10^6 for the newer layout. On the other hand, when product utilization was included, it resulted in (mostly) favored with the implementation of new technology. For example, when liquefied biogas (LBG) was utilized, carbon dioxide equivalent was -1.62 x 10^7 the original layout and -1.66 x 10^7 for the newer layout.
The process with most net influence on total impact of the biogas plant was the liquefication of biogas from anaerobic digestion (between 31 and 38%), followed by the heat treatment process (between 31 to 48%) within each layout (if gross impacts were considered), depended on the impact. It is noted that the impact came mostly from energy input as the process was assumed to have no leak to environment.
The model also assessed the performance when end products were to be utilized for benefit of the biogas plant. Utilization of end products was proven to bring benefits in term of reducing emissions, ranging from 0.68 to 1.52% for fertilizer spreading, or entirely negated by at least once, up to almost four times if CHP of final products was applied. The incorporation of hydrothermal carbonization (HTC) into the plant resulted in an increase by 65 tons of LBG, leading to more environmental impact negation when LBG was utilized, specifically 2.3 to 3.3% based on the categories. In the fertilizing scenario, HTC layout had more impact (0.7 to 5.3%) due to larger quantity of ammonia water needed to be transported. In the CHP scenario, the impact of HTC layout was much larger (up to 58%) compared to original layout. For the simulation with using LBG as fuel for a vehicle, it had 100 to 200 times less environmental impact compared to the same vehicle with petrol.
A sensitivity analysis also revealed there could be improvement potential if the choice of energy was altered toward “greener” option, with a decrease of 12-fold.
As a request for future research, it is recommended to focus on finding specific emission impact of unit processes to provide a more precise result in simulation.
This study quantified and compared the two operation layouts of a biogas plant in Finland, to see how the transition from old to new technology affect the performance in environmental aspect. The research was done through simulation with input based on the mass flow of the biogas plant.
The life cycle assessment model was built to compare the environmental footprints of the two layouts. It was found out that the more modern technology produced more emission equivalent by 1 to 8%, due to the chosen boundary, lack of proper input data, and efficiency value. Carbon dioxide equivalent was 3.89 x 10^6 for the original layout, and 4 x 10^6 for the newer layout. On the other hand, when product utilization was included, it resulted in (mostly) favored with the implementation of new technology. For example, when liquefied biogas (LBG) was utilized, carbon dioxide equivalent was -1.62 x 10^7 the original layout and -1.66 x 10^7 for the newer layout.
The process with most net influence on total impact of the biogas plant was the liquefication of biogas from anaerobic digestion (between 31 and 38%), followed by the heat treatment process (between 31 to 48%) within each layout (if gross impacts were considered), depended on the impact. It is noted that the impact came mostly from energy input as the process was assumed to have no leak to environment.
The model also assessed the performance when end products were to be utilized for benefit of the biogas plant. Utilization of end products was proven to bring benefits in term of reducing emissions, ranging from 0.68 to 1.52% for fertilizer spreading, or entirely negated by at least once, up to almost four times if CHP of final products was applied. The incorporation of hydrothermal carbonization (HTC) into the plant resulted in an increase by 65 tons of LBG, leading to more environmental impact negation when LBG was utilized, specifically 2.3 to 3.3% based on the categories. In the fertilizing scenario, HTC layout had more impact (0.7 to 5.3%) due to larger quantity of ammonia water needed to be transported. In the CHP scenario, the impact of HTC layout was much larger (up to 58%) compared to original layout. For the simulation with using LBG as fuel for a vehicle, it had 100 to 200 times less environmental impact compared to the same vehicle with petrol.
A sensitivity analysis also revealed there could be improvement potential if the choice of energy was altered toward “greener” option, with a decrease of 12-fold.
As a request for future research, it is recommended to focus on finding specific emission impact of unit processes to provide a more precise result in simulation.