Microplastic transport dynamics in surcharging and overflowing manholes

Ben Stride; Charlotte Dykes; Soroush Abolfathi; Modupe Jimoh; Gary D Bending; Jonathan Pearson

doi:10.1016/j.scitotenv.2023.165683

Microplastic transport dynamics in surcharging and overflowing manholes

Sci Total Environ. 2023 Nov 15:899:165683. doi: 10.1016/j.scitotenv.2023.165683. Epub 2023 Jul 20.

Authors

Ben Stride¹, Charlotte Dykes², Soroush Abolfathi³, Modupe Jimoh², Gary D Bending⁴, Jonathan Pearson²

Affiliations

¹ School of Engineering, University of Warwick, Coventry CV4 7AL, UK. Electronic address: ben.stride@warwick.ac.uk.
² School of Engineering, University of Warwick, Coventry CV4 7AL, UK.
³ School of Engineering, University of Warwick, Coventry CV4 7AL, UK. Electronic address: Soroush.Abolfathi@Warwick.ac.uk.
⁴ School of Life Sciences, University of Warwick, Coventry CV4 7AL, UK.

PMID: 37478932
DOI: 10.1016/j.scitotenv.2023.165683

Abstract

The transport of microplastics within urban water systems remains poorly understood, with little prior research on their behaviour within manhole configurations. This study represents the first to measure and model the transport dynamics of microplastics within circular and square manholes under different hydraulic scenarios. The transport and fate of polyethylene (PE) was quantified and compared to solutes (Rhodamine WT dye) using energy losses, residence time distributions (RTDs), and mixing models within surcharging and overflowing manholes. The bulk mass of solute and PE concentrations followed similar flow paths across all conditions except for 17.3 ± 7.9 % of PE mass that was immobilized in a dead zone above the inlet pipe for manholes with a surcharge to pipe diameter ratio ≥2. Consequently, these microplastics only exit after a significant change in hydraulic regime occurs, causing microplastics to be at risk of being contaminated over a prolonged duration. No significant mixing differences for PE and solutes were found between manhole geometries. The deconvolution method outperformed the ADZ model with goodness of fit (R_t²) values of 0.99 (0.60) and 1.00 (0.89) for PE and solute mixing, respectively. This establishes the deconvolution method as the most accurate and appropriate model to accurately predict microplastic mixing in manholes and urban drainage systems.

Keywords: Dead zone; Deconvolution; Mixing; Pollution transport; Polyethylene; RTD.