Pre-feasibility study on biomethane production from organic waste in the city of Tbilisi, Georgia

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Insinööritieteiden korkeakoulu | Master's thesis

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Date

2021-08-23

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Mcode

Degree programme

Nordic Master Programme in Innovative and Sustainable Energy Engineering (ISEE)

Language

en

Pages

95+7

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Abstract

Every day, the city of Tbilisi produces around 1000 tonnes of municipal solid waste. All of the waste is disposed of in the only landfill in the city, which is 14 km from the city. There is an increasing demand for natural gas for 200 natural gas buses purchased by the municipality in 2016. Anaerobic digestion could enable a biogas production that would add value to the waste and reduce the GHG emissions. In the country of Georgia, there are no anaerobic digestion plants, and the only way of dealing with the waste is through landfill disposal. There is a plan to implement a landfill gas capturing system in the landfill of Tbilisi. Anaerobic digestion (AD), compared with landfilling, presents many advantages, such as lower GHG emissions due to the high GWP of CH4 released into the atmosphere. AD also reduces the volume of waste and the land used. Furthermore, producing valuable products, anaerobic digestion has proven to be a viable investment. The main objective of this thesis is to evaluate the feasibility of a large-scale anaerobic digestion plant in the municipality of Tbilisi, considering the definition of large-scale, as often used referring to plants treating more than 3000 tonnes of substrate per year. The amount of organic fraction of MSW (OFMSW), animal sludge waste, waste from meat processing in Tbilisi and suitable for anaerobic digestion were fist evaluated. In the municipality of Tbilisi, the biomethane potential from the OFMSW residues showed that the it is the far most relevant of the substrates available, with a yearly biomethane potential 18.7-37.3 million Nm3. All the other substrates accounted for a yearly biomethane potential of 1.46 million Nm3. Hence, OFMSW has been assumed as the substrate and different digesters technology have been evaluated, pointing out the most effective for the characteristics of the OFMSW in Tbilisi. The effectiveness of the anaerobic digestion technologies available on the market were compared based on the specific biomethane yield per tonne of substrate. From the comparison the thermophilic, wet, one-stage and batch solution for a digester is the most economically feasible. Finally, an investment analysis was made based on the data of a budgetary quotation from an AD plant manufacturer. Following characteristics were evaluated: Discounted Pay Back Time (DPBT), Net Present Value (NPV) and Internal Rate of Return (IRR). The investment analysis was created based on a budgetary offer proposed by one of the biggest companies manufacturing large-scale anaerobic digestion plants. Keeping the values from the budgetary offer constant different scenarios were created, varying 3 parameters: the cost of digestate, cost of biomethane and taxes. Since the increase of price of CNG in Georgia increased between 2015 and 2018 of around 30%, it has been considered the scenario of 2021 and in 2024 assuming this increase in price being constant in the next years. The scenario which shows the best results is the one assumed to be in 2024, where the biomethane for vehicle cost is supposed at 0.93 €/kg, with NPV of the investment being 3.6-14 million euro. Even if we assumed that the growth in the price will increase constantly as it did between 2015 and 2018, to reach that price (lower than average price in Europe) it will need a few years.

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Supervisor

Järvinen, Mika

Thesis advisor

Khatiwada, Dilip

Keywords

large-scale anaerobic digestion plant, biomethane, investment analysis, Georgia

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https://urn.fi/URN:NBN:fi:aalto-202109209272

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[dipl] Insinööritieteiden korkeakoulu / ENG