Abstract
Wastewater treatment plants (WWTP) located in regions far from a high-pressure grid can produce renewable biomethane, which can partially substitute the natural gas locally consumed. However, the economic viability of implementing biomethane plants in WWTP has to be guaranteed. This paper uses the discount cash flow method to analyze the economic viability of producing biomethane in a WWTP located in Évora (Portugal). The results show that, under the current conditions, it is unprofitable to produce biomethane in this WWTP. Since selling the CO2 separated from biogas may result in an additional income, this option was also considered. In this case, a price of 46 EUR/t CO2 has to be paid to make the project viable. Finally, the impact of potential government incentives in the form of feed-in premia was investigated. Without selling CO2, the project would only be profitable for feed-in premia above 55.5 EUR/MWh. If all the CO2 produced was sold at 30 EUR/t CO2, a premium price of 20 EUR/MWh would make the project profitable. This study shows that the economic attractiveness of producing biomethane in small WWTP is only secured through sufficient financial incentives, which are vital for developing the biomethane market with all its associated advantages.
Highlights
The search for alternative energy sources is a present challenge for societies [1]
The indicators usually used to conclude if a project is profitable or not are the net present value (NPV), discounted payback time (DPBT), internal rate of return (IRR) and profitability index (PI)
Other parameters to highlight are the long DPBT obtained and a PI of −2.23
Summary
The need to find a replacement for fossil fuels emerged both because of the scarcity of known non-renewable fuel reserves and because of the environmental problems caused by greenhouse gas (GHG) emissions [2,3]. In this context, renewable energies have become important in the last decades mainly because of the sources from where they come [4,5]. Clear examples of such solutions involve the sludge produced in wastewater treatment plants (WWTP), which has a huge potential to be converted into energy or fuels [10], but in many cases still ends up in landfills [11,12]
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