The oxygen is injected into the aeration tanks via blowers. In small and medium-sized wastewater treatment plants, these are usually controlled by a timer – regardless of the actual contamination level in the wastewater influent. This approach also bypasses the dynamics of the biological processes in the aeration tank. The process usually operates on that assumption that “more is better”: better to aerate a little longer in order to ensure that the required limiting values are actually met. However, since the blowers require a great deal of power, this approach drives up the energy costs. Furthermore, an excess of oxygen impedes the stage following nitrification – denitrification – in which the nitrates that were generated are then reduced to molecular nitrogen. Therefore, the discharge values are not as low as they could be. The result is that plant operators often have to pay unnecessarily high wastewater charges.