Extraneous water in sewer systems: A Comprehensive review on sewer infiltration and inflow quantification, localization and mitigation

• Review of infiltration/inflow (I/I) quantification, localization & mitigation. • Evaluate spatial-temporal validity of I/I quantifying methods with respect to I/I component. • Report emerging I/I localization methods, their status and future development. • Propose a data-driven evaluation of I/I mitigation effect with respect to sewer component. Sanitary sewer systems are designed to convey wastewater from households and industries to wastewater treatment plants (WWTPs); however, in most cases they also collect a considerable amount of additional water via infiltration and inflow (I/I). I/I not only increases the conveyance and treatment burden but also places threats on sewer overflow and ground collapse. The various sources of I/I and sewer components (i.e., sewer mains, sewer laterals and maintenance holes) and their interactions make the I/I detection, analysis and mitigation challenging in practice. Abundant research has addressed I/I quantification, I/I localization and sewer rehabilitation respectively, which provides substantial amount of knowledge and data for advising I/I mitigation. Nevertheless, there is a lack of a systemic overview of these research efforts and an integral analysis and synthesis of these research outcomes (including knowledge, tools, methods and data), which hinders the effective use of these researches for advising on I/I mitigation and advancing future research. To address this gap, a systematic review was conducted. The study synthesized the suitability and limitations of various quantification methods, assessed the applicability of I/I localizaiton methods across different contexts, and developed a data-driven model to estimate I/I reduction effectiveness based on the rehabilitation degree of sewer-network components, including sewer mains, sewer laterals, and maintenance holes to support planning of future I/I mitigation and sewer rehabilitation. To this end, correlating the extent of sewer-component-specific rehabilitation and the I/I reduction rate may be a potential data-driven approach to support I/I mitigation, as briefly demonstrated in this study.