Evaluation of Combined Sewer System Operation Strategies Based on Highly Resolved Online Data

Abstract

Operational and structural interventions in the field of stormwater management are usually planned based on long-term simulations using rainfall-runoff models. The simulation results are often highly uncertain due to imperfections of the model structure and inevitable uncertainties of input data. The trend towards monitoring of combined sewer overflows (CSO) structures produces more and more data which can be used to replace parts of the models and reduce uncertainty. In this study we use highly resolved online flow and quality monitoring data to optimize static outflow settings of CSO tanks. In a second step, the additional benefit of real time control (RTC) strategies is assessed. In both cases the aim is the reduction of CSO emissions. The methodology is developed on a conceptual drainage system with two CSO tanks and then applied to a case study area in Southern Germany with six tanks. A measured time series of six months is sufficient for reliable optimization results in the conceptual catchment as well as in the case study area system. In the investigated system the choice of the optimization objective (minimum overflow volume or total suspended solids (TSS) load) had no significant influence on the result. The presented method is particularly suitable for areas in which reliable monitoring data are available, but hydrological parameters of the catchment areas are uncertain. One strength of the proposed approach lies in the accurate representation of the distribution of emissions between the individual CSO structures over an entire system. This way emissions can be fitted to the sensitivity of the receiving water body at the specific outlets.

Towards the long term implementation of real time control of combined sewer systems: a review of performance and influencing factors

“…Extrapolation methods from smaller data sets have been proposed (Meneses et al 2018), but their underlying assumption of linearity between increased rainfall depth with CSO volume is one that does not hold (Vezarro 2021). For the design of optimal RTC, on the other hand, convergence to an optimum can happen faster, within 10 events for the catchment studied by Bachmann-Machnik et al (2021). However, the size of the catchment and lack of uncertainty analysis contribute to this relatively fast convergence.…”

“…Considering the cases of Dresden, Germany and Vienna, Austria, more modest yet significant theoretical reductions of 37.5 and 13.4% of CSO volume could be reached (Fuchs et al 1999;Fuchs & Beeneken 2005). On the other hand, several studies report low efficacies of RTC, some with a CSO volume reduction as low as 0.3% (Bachmann-Machnik et al 2021), despite indications that RTC might be a useful optimisation tool given the catchment characteristics as outlined in PASST. These discrepancies are a factor that might limit the uptake of RTC in practice, as the significant upfront costs to find out if there is potential for RTC might deter operators from exploring the potential.…”

Combined sewer overflows: relating event duration monitoring data to wastewater systems' capacity in England

“…38 However, just knowing Environmental Science: Water Research & Technology Paper how often and for how long individual CSOs operate, not much can be said about the reasons of their increased frequency and duration, nor about their pollution load. Instead, the impacts from CSO discharges depend on the volume discharged, their pollutant load which varies from community to community depending on the size of the wastewater system and the relative amounts of domestic, commercial, and industrial wastewater components collected by the sewers for treatment, [39][40][41] as well as the dilution factor and other characteristics of the waterbody they discharge into (i.e., sensitivity and value). 42,43 While it may be obvious that CSOs discharge more frequently when the systems they are connected to have less capacity, in this work, by estimating the capacity of these systems uniformly for the first time, we are able to investigate the extent to which increases in the frequency and duration of CSO spills are down to the lack of capacity of wastewater systems in the country.…”

“…38 However, just knowing how often and for how long individual CSOs operate, not much can be said about the reasons of their increased frequency and duration, nor about their pollution load. Instead, the impacts from CSO discharges depend on the volume discharged, their pollutant load which varies from community to community depending on the size of the wastewater system and the relative amounts of domestic, commercial, and industrial wastewater components collected by the sewers for treatment, 39–41 as well as the dilution factor and other characteristics of the waterbody they discharge into ( i.e. , sensitivity and value).…”

Efficient job list creation for long-term statistical modelling of combined sewer overflows

“…Some studies have focused on how to reduce the computational burden when analyzing urban drainage systems; either by exploring the link between rainfall properties and overflow phenomena in the sewer systems (Jean et al 2018;McGrath et al 2019), by utilizing machine learning techniques to avoid physics based models for flooding (Löwe et al 2021;Vorobevskii et al 2020) or by introducing model predictive or real time control into the system (Rathnayake and Faisal Anwar 2019;Bachmann-Machnik et al 2021;El Ghazouli et al 2021). Common for all studies is a recognition of the complexity involved in determining the performance of urban drainage systems, and a goal of minimizing the efforts involved in designing, analyzing and operating these systems.…”