Any sewage treatment plant receives waste water that has oil, suspended particles and settable particles. Apart from this there are sometimes other undesirable articles like condoms, sanitary pads, plastics comes in to the plant. These materials are removed by screening process in large sewage treatment plants by employing mechanical processes and operators. When it comes to small sewage treatment plants these particles cannot be removed on a daily basis and have to be accommodated in the collection for a longer period of time before removal. Also , a small sewage treatment plant is exposed shock loads and low loads more frequently than larger plants. Thus smaller the plant, the proportion of holding capacity would be larger to overcome uncertain conditions and to operate the plant without the need for operator. A compact small sewage treatment plant will always have more problems than liberally designed small sewage treatment plant.