Grant Award Year: 2019
Principal Investigator:
Amy Mueller, Civil and Environmental Engineering, Northeastern University
Edward Beighley, Civil and Environmental Engineering, Northeastern University
Research Description:
The Charles River, which receives stormwater runoff from the City of Cambridge, is impaired by eutrophication. To meet Total Maximum Daily Load (TMDL) allocations for phosphorous, the City is executing its Long-Term Control Plan which includes separating sanitary and stormwater sewers, however structural and non-structural Best Management Practices are still needed to treat stormwater prior to its entering receiving water. To achieve this, flow controls are being considered to selectively direct (ideally high P) portions of stormwater to the Deer Island Wastewater Treatment Plant, but this raises two key questions: (i) which fraction(s) of stormwater flows should be diverted to the WWTP, given limits on how much additional flow the WWTP can handle, and (ii) how can a real-time control system be implemented to automatically manage this process? Previously best understanding indicated that P loads are maximum during a storm’s 'first flush' and associated with a specific particle size fraction, conditions which could be selected for by measuring velocity. However, preliminary high-resolution data collection conducted by this team in 2018 over a number of storm events has shown this is not universally true, geographically or temporally, and therefore a more complete understanding and control strategy is needed. In response, this project envisions a pathway to real-time estimation of P flux in storm waters through (1) installation of real-time sensing modalities for estimation of water chemistry at storm sewer diversion points and (2) using these data to calibrate both hydraulic and machine learning models to identify reliable real-time predictors of P flux. While an obvious next step, achieving these goals requires overcoming the lack of commercial real-time P sensors and difficulties/costs associated with data collection during storm events (major contributors to P exports), which prevents a traditional machine learning 'big data' approach.
Report
Project Type: Annual Base Grant
Project ID: 2019MA133B
Project Impact:
The primary achievements of this project were the evaluation of a range of physical parameters and sensors signals for accurate and/or real-time quantification of phosphorous fluxes in separated stormwater sewers in highly urbanized areas. Six wet weather events were studied in 2019-20 at 6 different sites in two cities. A range of parameters were measured in real-time by sensors (e.g., flow, level, conductivity, pH) while others were measured through lab analysis on collected samples ( TSS, orthophosphate, total phosphorous, and total phosphorous in subsamples filtered to four different size fractions). The main findings of this work are, contrary to the conclusions of prior studies which focused primarily on non-urban waters:
- the fraction of P in dissolved versus particulate form is highly variable, with dissolved fraction representing 0-40% of P flux, meaning online measurements need to characterize both orthophosphate and particles to be useful for the stated purpose, and
- the size of particles with which phosphorous is associated varies not only by site but also by wet weather event, i.e., particle loading and/or water velocity are not accurate proxies for phosphorous flux.
These insights directly informed the design of next -generation of online instrumentation for this study (constructed Fall 2020, being deployed 4/2021) including characterizing the dissolved phase constituents (7 ion selective electrodes for nutrients, as fluxes may be correlated with P fluxes, and metals, which may account for some non-P related particulate loading) as well as bulk properties related to dissolved and particulate phases (conductivity, DO, pH, turbidity).
Information Transfer:
This project directly led to recommended design for a high resolution stormwater monitoring station within the City of Boston (work funded through the Boston Water and Sewer Commission). This new system will go online in Q2 of 2021, collecting data online for a range of parameters, including both bulk characterization of water and nutrients. These data will contribute to improvement/validation of the City model for nutrient (primarily phosphorous) and other pollutant (nitrogen, TSS, zinc, copper) loading to the Charles River.
Products:
Khan. ST et al. "Dynamic stormwater management to mitigate phosphorous export." Science of the Total Environment. (In revision; resubmission due late March)
Students supported (Number of students, degree pursued, Major):
As that the funding from USGS was primarily an equipment grant, please note that the list of students supported indicates students who worked on this project (educational and mentorship support) but undertook this work as part of their education (e.g., research for credit), undertook this work as a volunteer, or were paid through other sources.
- Graduate students: 1 (PhD, Civil & Environmental Engineering)
- Undergraduate students: 5 (UG: 1 in Chemistry, 3 in Civil & Environmental Engineering, 1 in Environmental Geology & Chemistry)
Notable Achievement and Awards:
Preliminary results from this work resulted in award of a contract (<$250k) with the Boston Water and Sewer Commission (subaward via Kleinfelder as part of a larger project) for a high resolution study of Boston stormwaters during 2020-22.