DEVELOPMENT OF COST FUNCTIONS AND COST INDICES FOR PREDICTING COST OF SEWAGE TREATMENT PLANTS

摘要

Cost functions (CFs) and cost indices (I_(STP)) are useful tools for predicting the costs of sewage treatment plants (STP) for the base year and for updating the costs to different years respectively. The paper presents the study on the development of CFs and I_(STP) for STPs based on Activated Sludge Process (ASP). Design and estimation (DEST) models have been developed in Microsoft Excel Spread Sheet for designing, estimating and deriving unit cost of STPs in the base year of 2014.A typical process flow sheet of STP based on ASP including sludge management has been adopted. Unit cost data derived from the DEST model have been used for the development of CFs by regression analysis for the base year of 2014. I_(STP) have been developed, with a basket of nine cost items and their weights derived from DEST model using Laspeyres formula. It was found that there is a correlation between I_(STP) and construction cost indices (CCI) published by Construction Industries Development Corporation with a fixation factor of 0.973. The accuracy of predictions of costs of STPs based on ASP with CFs and I_(STP) was found to be of very high accuracy for small and medium capacity groups of STPs and good accuracy for large capacity group STPs. Unit costs of STPs based on ASP for 78 cities have been derived and presented as a ready reckoner.