Abstract
Decentralized treatment of stormwater runoff from heavily polluted surface can be a good solution for effective source control. Decentralized stormwater treatment systems (DS) and test procedures to monitor their performance, have been developed in recent years. At present in Germany, only lab-based tests are officially established to determine the removal efficiency of Total Suspended Solids (TSS), and in situ monitoring is still lacking. Furthermore, the fine fraction of TSS with particle sizes less than 63 µm (TSS63) have been established as a new design parameter in Germany, because of their substitute characteristics of adsorbing pollutant substances. For research and evaluation purposes continuous data of urban stormwater runoff quantity and quality at the in- and outflow of two different DS at two different sites were collected. Turbidity is used as a surrogate for TSS. Continuous turbidity data and time proportional sampling served to obtain (i) regression coefficients and (ii) to determine the TSS removal efficiency of DS. For a wide range of events the total removal efficiency of DS1 was 29% for TSS and 19% for TSS63 and for DS2 19% for TSS and 16% for TSS63. An event-based data analysis revealed a high variability of the efficiencies and its uncertainties. Moreover, outwash of still suspended or remobilization of already deposited material was observed at individual events. At both sites TSS63 dominates urban stormwater runoff as indicated by the mean ratios of TSS63 to TSS of 0.78 at the inflows and 0.89 at the outflows of both DS. A significant shift of TSS63 ratio from inflow to outflow demonstrates that TSS63 particles were removed less efficiently than coarser particles by DS1, for DS2 data was too heterogeny. It clarifies that common sedimentation methods can only contribute to a small extent to the reduction of solid emissions if the stormwater runoff contains mainly fine-particle solids. The findings suggest that treatment of urban stormwater runoff with high TSS63 pollution requires additional techniques such as a proper filtering to retain fine particles more effective.
Highlights
The water quality, ecology, and microbiology of receiving rivers are influenced by separate and combined sewer outlets, in addition to direct street runoff (e.g., [1,2,3])
The findings suggest that treatment of urban stormwater runoff with high TSS63 pollution requires additional techniques such as a proper filtering to retain fine particles more effective
Selection of samples with higher TSS63 ratio for regression of turbidity to Total Suspended Solids (TSS) can lead to a lower slope, whereas exclusion of high leverage samples can have an effect in both directions
Summary
The water quality, ecology, and microbiology of receiving rivers are influenced by separate and combined sewer outlets, in addition to direct street runoff (e.g., [1,2,3]). Urban runoff transports high loads of particles that act as main vector for particle-bound pollutants [4,5,6]. High concentrations and annual loads of heavy metals (Zn > Cu > Pb) have been detected in urban storm water which originated from vehicle brake emissions, tire wear, roof covering materials or atmospheric deposition [4,5,7,8,9,10]. The loads of heavy metals rise [11] and correlate significant to fine fraction of Total Suspended Solids (TSS63, with particles sizes of 0.45 μm < TSS63 < 63 μm) [12]. Based on studies of Hilliges et al (2017), Dierschke and Welker (2015), Zhao et al (2010) and Selbig (2015) that focus on distribution and pollution of particles in road runoff, TSS63 was implemented in 2020 as a new design parameter in German stormwater management regulation [12,13,14,15,16]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
