Design of Sewerage System for Rural Human Settlement: A Case Study

Abstract

In the present study for rural human settlement, a sewerage system in Kanech village near Ludhiana has been designed. Being a village with human population of 3422 and cattle population of 767, for keeping the sewer depth within limits and for having four smaller STP at the four village ponds, simplified sewerage system has been opted. Based on surface drainage patterns, village was divided into four zones. For each zone a separate simplified sewerage system and sewage treatment plant integrating the village pond was planned. For each of the village zones, sewer map was divided and sewer stretches and manholes needed were finalized. For each of sewer stretch through survey and population forecasting both present and design peak flow were worked out. Design peak flow were worked out through assuming increase of population at 1.22 percentage per year (The value affirmed by Punjab state water supply and sanitation board) and through identifying new areas of development and assessing their population densities when fully developed. A typical water consumption rate of 135 lpcd has been considered for the designing purpose. A peaking factor of 2.4 was assumed for this designing purpose. Cattle tanks were planned to handle the dung of the village. For ensuring selfcleansing velocity through the sewers from the beginning in order to have some sufficient minimum flow automatic siphoned system were planned into the sewerage system. Two size of siphon system one to serve upto 15 people and the other to serve up to 50 people have been provided. These siphons are to deliver a maximum of 8lps of sewage when running. This 8lps has been taken as the minimum peak flow for the sewerage system design. Instead of 0.4m, as per the advice of PSWSSB, a minimum cover of 0.9m was assumed for the sewer. The design approach of Bakalian and modified by Duncan Mara was followed in the sewer design. Using the present peak flow, minimum slope was worked out on the basis of ensuring minimum tractive tension of 1.5Pascals. Diameter of the sewer was then decided on the basis of design peak flow while ensuring d/D ı 0.8. Depending on the need three types of manholes, simplified manholes, junction manholes and drop manholes were provided. Simplified manholes were used only in those stretches where sewer depth was ı 1.65m. For sewer depth ı1.65m, rectangular and circular manholes of conventional sewerage system were used as per IS: 4111(part1)-1986. For comparison and appreciation of the merits of simplified sewerage system for one of the four zones, even conventional and small bore sewerage system were designed. In case of small bore system intercepting tank were provided at household level .The automatic siphon systems have been considered even for the conventional sewerage system. All design detail of both the small bore and conventional sewerage system has been including in the detailed project.