Large Sewage treatment plants are the municipal plants which are connected to sewer networks. Wastewater flows many kilometres before reaching the treatment plant. There is reduction of load during the flow and also losses due to evaporation, infiltration, etc. Moreover, the flow into the plant on a hourly/ daily basis would remain the same due to long distance sewer lines. On the other hand small sewage treatment plants are localized to communities and it takes only minutes for the wastewater to flow into the sewage treatment plant. Also there is no losses in water as most pipelines are plastic and there is no loss of load that is expected in a large sewage treatment plant. The collection and equalisation should be a key factor in designing these small sewage treatment plants for proper performance. Also there are varying loads depending on the building type. Schools and offices are closed on weekends, for which intelligent control systems and designs are necessary in small sewage treatmen plants, which are not so important in larger muncipal plants.