This question is generally asked to test your basic knowledge about the operation of machinery as we all know that if onboard STP is of anaerobic type then the microorganism break down biodegradable material in the absence of oxygen, but if it is of aerobic type then definitely STP will not work because Aerobic digestion is a bacterial process occurring in the presence of oxygen. If, however, there is insufficient oxygen for these bacteria then alternative bacteria dominate. These Anaerobic Bacteria produce Hydrogen Sulphide, Methane and Ammonia. These gasses are either highly toxic or flammable or both. In particular, Hydrogen Sulphide is toxic to humans in concentrations down to 10ppm and its flammable vapours are heavier than air so may build up in lethal pockets in enclosed spaces. So, if the blower stops working the aerobic bacteria may die and it will take a longer time to regenerate.