The odour is indeed neutralised as it is within an enclosed system. However, from my understanding, there aren't 3 distinct layers of biofilms, but rather 1 layer of biofilm. From wikipedia, a biofilm is "any group of microorganisms in which cells stick to each other and often these cells adhere to a surface.
These adherent cells are frequently embedded within a self-produced matrix of extracellular polymeric substance (EPS)". In short, the biofilm grows as the microorganisms (protozoa and metazoa) in the water oxidises reduced nitrogen and carbon using oxygen (which is fed through the hollow fibre membrane) to both generate biomass (used for energy) and excrete EPS.
The secretion of EPS allows the microorganisms to aggregate together and form a floc which effectively increases the size of biofilm; this film grows bigger and bigger over time as carbon and nitrogen in the wastewater are being oxidised. When it gets too big, a part of this biofilm disperses/falls and moves on to the secondary clarifier along with the treated water.
The wastewater / treated water from the Emefcy MABR's will then be transferred into secondary clarifiers where solids sedimentation takes place. Solids in the form of volatile solids (organic carbon/nitrogen and microorganisms) and non-volatile solids (dirt, tiny rocks, etc) will sink over time due to a higher density (sedimentation) and this is what we call "activated sludge".
RAS = Return/Recycle Activated Sludge
WAS = Waste Activated Sludge
The purpose of RAS is to maintain a sufficient concentration of activated sludge in the MABR module so that the required degree of treatment can be obtained in the time interval desired. As previously mentioned, there is a loss of bacteria happening in the MABR module as the biofilm gets too big which is compensated by RAS. In addition, there could just be insufficient bacteria as the process is operating in its early stages. WAS stream is where the rest of the volatile and non-volatile solids go to.
The treated water (top part of the clarifier) is constantly fed to another stream where it enters tertiary filtration and some other purification step before being considered as an effluent.
(20min delay)