Qualified environmental engineering companies are the ones who should be engaged in the designing of sewage treatment plants. Each sewage treatment plant requires different design based on type of usage and building type. Office, schools, colleges, resorts, communities, hospitals, industries and independent homes, each need specific design for the plant to work without problem. Most designers are unaware of difference of peak factor, peak load for equalisation tank design. There is a need to understand sludge volume index, MLSS, activated sludge, sludge age with respect to the plant type. There is something called oxygen transfer efficiency for the choice and design of aeration grid and choice of compressor, which is determined by the water working depth and flow. Although, not rocket science- it is better to work with technology companies that are expert in sewage treatment plant design to be sure that you get a performing plant.