The untreated sewage disposed can cause pollution and diseases, which is why it is best to treat the sewage. The pollutants are removed by biological, physical and chemical processes. The commercial STP plant separates the water and sludge. The water can be re-used in certain areas and the sludge delivered is clean and environment friendly. The installation of STP plant requires connection to the mains sewers. This treatment plant must be installed only by professionals. Moreover, it requires annual professional maintenance.