Modelling of sanitary sewer systems integrating rainfall-derived infiltration and inflow

Abstract

Wastewater utilities often have management difficulties when excessive wet-weather flow leads to serious impacts in public health and environment as well as disturbing operational conditions in wastewater treatment plants (WWTP). This phenomenon, resulting from rainfall-derived infiltration and inflow (RDII), occurs mainly due to defects in pipes and manholes (infiltration) and to illicit connections from downspouts, foundation drains or cross-connections with storm sewers (inflow), contributing to sanitary sewer overflows (SSOs). These difficulties related to SSOs negatively affect: (i) the capacity and operation of sanitary sewer collection; (ii) the performance and treatment efficiency of WWTP; (iii) the risk of a public health hazards and environmental contamination. This well-known wastewater managerial problem is very difficult to locate and quantify in practice since the needed adequate measurement equipment often entails unsustainable costs for utilities. Wastewater flow mathematical modelling integrating a digital cadastral database using Geographic Information Systems (GIS) constitutes a sound methodology in predicting sanitary sewer systems performance which is a critical issue within SSOs reduction and remediation programs. This paper presents the implementation of a methodology based on hydroinformatic tools to determine the contribution of RDII in complex municipal sewer systems in order to establish adequate urban wastewater management policies that will effectively mitigate SSOs. USEPA SWMM, and digital cadastral database with field verification were applied in a simulation study of the small scale sanitary sewer network of Espinho (Braga, Portugal) whose results will be used in a larger scale to create a city-wide model for wastewater systems management.