There is food required for the bacteria to form and live in stable conditions. The air supplied in the aeration chamber should be adequate. In a classical continuously operated plant, the incoming water should be both adequate in flow and pollutant content (food for bacteria). During the start up period there is lower volume of flow into the aeration chamber, in other words the plant cannot be fed continuously. Therefore there will be either low levels of bacteria due to lower availability of food. In a SBR plant, this situation is overcome by sequencing the batches according to the incoming water volume. For example, during the start up period, the plant can run one batch in a day by reducing the aeration period in multiple on and off cycles. By this way, both the bacteria population and the water load is distributed by means of a program. When the occupancy and flow increases, the program can be adjusted to operate more number of cycles in a day.