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Lookup NU author(s): Professor Adam Jarvis, Dr Catherine GandyORCiD
This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).
© 2026 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license. http://creativecommons.org/licenses/by/4.0/. The performance of an innovative compost-based passive bioreactor employing bacterial sulfate reduction to treat mine water containing modest metal concentrations in a short hydraulic residence time (15–20 h) was investigated. The full-scale experimental system comprised two parallel vertical flow ponds, each divided into four equal-area quadrants to enable detailed spatial assessment of treatment variability. Over 5.5 years of operation, mean filtered Zn removal efficiencies of 92.5% and 91.8% and mean volume-adjusted Zn removal rates of 1.59 g/m3/day and 1.75 g/m3/day were achieved in VFP1 and VFP2, respectively. Mean sulfate reduction rates of 71.0 mmol/m3/day and 74.6 mmol/m3/day were also recorded, despite a low influent sulfate concentration (mean 26.4 mg/L). To the authors' knowledge, this represents the first system worldwide to achieve effective metal removal via bacterial sulfate reduction at such low influent sulfate concentrations. Spatial variability in Zn removal and sulfate reduction was attributed to differences in hydraulic behaviour resulting from reduced substrate permeability and short circuiting, complicating prediction of overall system performance. Precise control of hydraulic and contaminant loading rates enabled system optimisation, with maximum Zn removal, and hence greatest benefit to the receiving watercourse, achieved at flow rates of 4–4.5 L/s. These results demonstrate that short hydraulic residence time compost bioreactors can effectively remove metals from mine waters with relatively low contaminant concentrations. The findings highlight their potential for the passive treatment of discharges from abandoned metal mines, particularly those typical of the UK, with modest metal concentrations and requiring small treatment system footprints.
Author(s): Jarvis AP, Cox NJ, Potter HAB, Gandy CJ
Publication type: Article
Publication status: Published
Journal: Ecological Engineering
Year: 2026
Volume: 229
Print publication date: 01/08/2026
Online publication date: 13/05/2026
Acceptance date: 05/05/2026
Date deposited: 26/05/2026
ISSN (print): 0925-8574
ISSN (electronic): 1872-6992
Publisher: Elsevier BV
URL: https://doi.org/10.1016/j.ecoleng.2026.108024
DOI: 10.1016/j.ecoleng.2026.108024
Data Access Statement: Data will be made available on request.
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