Field validation of a new low-cost method for determining occurrence and duration of combined sewer overflows

Combined sewer overflow (CSO) events produced in combined sewer systems (CSS) during wet weather conditions are a threat for the receiving water bodies. The large number of CSO structures normally present in a CSS makes that the monitoring of the complete CSO network in a simultaneous way would drastically increase the investment costs. In this paper, a new methodology is presented aiming to characterize the occurrence and duration of CSO events by means of low-cost temperature sensors. Hence, a large number of CSO structures can be simultaneously monitored and the system can be characterized as a whole. The method assumes temperature differences between the overflowing mix of wastewater and stormwater and the sewer gas phase, so the temperature shift produced during a rainfall episode is related to a CSO event occurrence. The method has been tested and validated in La Garriga CSS (Spain) where the temperature at 13 CSO weirs was monitored for a period of 1. year (57 rainfall episodes). For the whole set of CSO events, occurrence and duration were successfully determined in 80% of cases. Advantages, limitations and potential applications of the method are discussed at the end of the paperThe authors would like to thank Consorci per la Defensa de la Conca del Riu Besòs (CDCRB), the Spanish Ministry of Science and Innovation (ENDERUS) (CTM-2009-13018), Spanish National Project (CTM-2011-27163), Juan de la Cierva (jci-2009-05604, FPI BES-2010-039247), and European Union (FEDER-CTM2009-13018). In additionwould like to thank to the staff from Drenatges Urbans del Besòs for their constant support. Also the Marie Curie IRG within the 7th European Community Framework Programme, FP7-People-2010-IRG-277050 and a Marie Curie Career Integration Grant PCIG9-GA-2011-29353