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KEB-23606 Biogas Technology for Material Flow Management and Energy Production
Exam 15.12.2017 Names of Examiners: Prof. Jukka Rintala, Dr. Pritha Chatterjee

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1. Discuss how to select feedstock(s) for a biogas system. Consider the process operation and digestate
utilization. What are the important feedstock characteristics and how they impact? (12 pts)

2. Discuss how to decide the reactor/process type for your biogas plant. Which factors are important?
Why to select dry, wet, thermophilic, plug flow etc. process (12 pts)

3. Biogas plant is treating 20 000 t of food industry biowaste. The VS is 20%, methane potential 500
M/tVS, and nitrogen content 2 % of VS.
a) What is the reactor volume if design load is 3 kgVS/md (4 pts)

b) How much vehicle fuel (biomethane) can annually be produced and how many cars could
annually be operated by that amount? Assume: the conversion efficiency in biomethane
production is 97%, methane consumption is 5 m methane/ 100 km, annually is driven 20 000
km/car. (4 pts)

c) For how many hectares the digestate could be spread ? Assume, that the annual fertilizing
amount is on 110 kgN/ha, the specific weight of digestate is one, and no nitrogen is lost during
the biogas process (4 pts)