REP Bioenergy and Waste-to-Energy 3

Question 1

In anaerobic digestion, the acetogenesis stage converts volatile fatty acids into which compounds?

Accepted Answer

Acetic acid, hydrogen, and carbon dioxide

Answer

Acetogenesis converts propionate and butyrate into acetic acid, H2, and CO2, which methanogenic archaea then use to produce methane.

Question 2

What is the typical biogas methane content range produced from well-operated anaerobic digesters?

Accepted Answer

55–75%

Answer

Anaerobic digesters typically yield biogas with 55–75% methane, the remainder being mostly CO2 with trace H2S and water vapor.

Question 3

Which co-digestion feedstock is most commonly added to municipal sewage sludge to significantly boost biogas yields?

Accepted Answer

Food waste and fats, oils, and greases (FOG)

Answer

Food waste and FOG are carbon-rich substrates that enhance anaerobic digestion when co-digested with nitrogen-rich sewage sludge, increasing methane yields.

Question 4

The Boudouard reaction in gasification describes the equilibrium between carbon, CO2, and which product gas?

Accepted Answer

Carbon monoxide

Answer

The Boudouard reaction (C + CO2 ⇌ 2CO) is endothermic and produces carbon monoxide from char and CO2 at high temperatures.

Question 5

Which type of biomass combustion system is best suited for fuels with widely varying particle sizes and moisture content?

Accepted Answer

Stoker/grate-fired boiler

Answer

Stoker/grate-fired boilers can accommodate heterogeneous fuels with variable sizes and up to 60% moisture without extensive pre-processing.

(REP) Certified Renewable Energy Professional Practice Test

(REP) Certified Renewable Energy Professional Practice Test

REP Bioenergy and Waste-to-Energy 3