OPTIMAL SEWER REHABILITATION DECISION MAKING MODELS CONSIDERING INFLOW/INFILTRATION

摘要

Inflow/Infiltration (I/I), which occurs through sewer defects, is a main factor in lowering the carrying capacity of sewers and the treatment efficiency of waste treatment plants. An I/I survey in a drainage district is executed by sampling water quantity and quality while considering the constraints of time and cost. Also, sewer rehabilitation methods in a drainage district use a numerical weighting method, quantitative approach, to determine the priority order in selecting areas to rehabilitate by analyzing the results of the water quantity and quality samples and the severity/degree of defects in the sewer. This study develops two models, an I/I Calculation Model (IICM) and a Sewer optimal Rehabilitation decision-making System Model (SRSM). The IICM considers two groups of factors. One group is I/I influencing factors: sewer diameter, sewer length, sewer material, sewer installation year, road width, and sewer slope. The other group is sewer defects such as cracks, projecting segments, corrosion, waste oil contamination and so on. The SRSM is formulated by using Genetic Algorithm (GA). In conclusion, IICM can calculate and distribute the total I/I of a specific area of a drainage district to each pipe in the entire drainage district. The SRSM can logically determine the priority of rehabilitation so that an optimal budget plan for the rehabilitation can be obtained and the efficiency of wastewater treatment can be enhanced. As a result, a detailed and systematic sewer rehabilitation plan can be established by applying a combination of the two models developed in this study, thus resulting in a significant saving in time and cost in rehabilitation of sewer systems.