Detection of extraneous water ingress into the sewer system using tandem methods - a case study in Trondheim city.

M Beheshti,S Sægrov

doi:10.2166/wst.2019.057

Abstract

Infiltration and inflow (I/I) of extraneous water in separate sewer systems are serious concerns in urban water management for their environmental, social and economic consequences. Effective reduction of I/I requires knowing where excess water ingress and illicit connections are located. The present study focuses on I/I detection in the foul sewer network of a catchment in Trondheim, Norway, during a period without snowmelt or groundwater infiltration. Fiber-optic distributed temperature sensing (DTS) was used for the first time in Norway to detect I/I sources in tandem with closed-circuit television inspection (CCTV) and smoke testing. DTS was an accurate and feasible method for I/I detection, though it cannot identify exact types of failure and sources of I/I. Therefore, other complementary methods must be used, e.g. CCTV or smoke testing. However, CCTV was not completely useful in confirming the DTS results. This study provides practical insights for the rehabilitation and repair of sewer networks that suffer from the undesirable I/I of extraneous water.

Highlights

Separate sewer networks efficiently and reliably convey foul sewage to wastewater treatment plants
This study demonstrated that distributed temperature sensing (DTS) in combination with supplemental methods is effective at locating individual infiltration and inflow (I/I) sources in sewer pipelines
The performance of the foul sewer system of Lykkjbekken catchment in Trondheim was assessed for detection of rainfall-derived I/I sources and illicit connections by various methods

Summary

Introduction

Separate sewer networks efficiently and reliably convey foul sewage to wastewater treatment plants. I/I from extraneous water and illicit connections can overload the sewer system, cause sanitary sewers to overflow, threaten public health, and increase energy and chemical consumption during treatment while decreasing overall treatment efficiency (Beheshti & Sægrov a). This specific concern threatens sustainable asset management of sewer infrastructure in the long term and reduces environmental, social and economic sustainability (Beheshti et al ; Beheshti & Sægrov a).

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Conclusion