The diagram shows an overview of the Henriksdal wastewater treatment process in Stockholm, Sweden. 
[Source: Stockholm Water Company and Dr Daniel Hellstrom: adapted from D Hellström, et al., (2009), BIOGASMAX - Integrated Project No 019795, Optimisation Activities at Stockholm Site Status of Biogas Production at Henriksdal plant 2000-2005, page 10]
State a group of organisms that will be active in the fermenter labelled X.
bacteria OR archaeans OR methanogens ✔
Deduce, with a reason, whether X is a continuous fermenter or a batch fermenter.
continuous because there is a constant input of raw materials ✔
Probes are used to monitor significant variables within the fermenter. List three significant variables that should be monitored in the fermenter.
a. pH/acidity/alkalinity ✔ b. foam ✔ c. metabolites ✔ d. substrate ✔ e. oxygen ✔ f. carbon dioxide ✔ g. temperature ✔ h. pressure ✔
Accept other valid condition
State the main component of biogas.
