Because the SBR operates ...

Because the SBR operates under aerobic followed by anaerobic conditions, without full aeration produced by fine bubble aeration, oxygen will not be transferred effectively.  This will cause permanent anaerobic conditions in part of the tank. It appears that iron bacteria have also grown locally in the areas around the diffusers and these would form crystallised material.  The other issue I would expect would be foaming from such a plant due to the stress reaction of aerobic bacteria.  It does stress the importance of inspecting submerged aeration membranes on a regular basis.  These damage is most likely to be natural events caused by the aeration system rather than deliberate sabotage.