Carbon dosing of denitrifying bioreactors to remove nitrate from agricultural drainage
type: CreativeWork
description: Several studies have demonstrated that denitrifying woodchips bioreactors effectively remove nitrate from a broad spectrum of wastewater. Even though bioreactors have a comparatively small spatial footprint and are straightforward to construct, the low long-term nitrate removal efficiency they provide compared to other mitigation options, such as constructed wetlands, may limit their utilization by catchment managers and landowners. This thesis investigated the use of external carbon dosing in bioreactors to improve nitrate removal and quantified some potential adverse effects of carbon dosing on bioreactors and downstream aquatic environments. Through observations ranging from field to mesocosm experiments, this thesis sought to (1) determine whether and to what extent external carbon dosing could improve nitrate removal in bioreactors and (2) assess the potential adverse effects of carbon dosing, such as reduced hydraulic performance and pollution swapping. The first component of the study evaluated the carbon dosing of a pilot-scale (58 m³) bioreactor treating drainage waters from a 0.65 ha paddock on a dairy farm. The effects of carbon dosing on the bioreactor's nitrate removal rates were assessed following a constant dosage of 8% (v/v) methanol solution at 10 mL min⁻¹ to the bioreactor's inlet distributor. Sulfate reduction and losses of added methanol from the bioreactor’s outlet were quantified as the potential adverse effects of external carbon dosing. Methanol dosing increased seasonal nitrate removal rates to 8 g N m⁻³ day⁻¹ in 2020 and 5 g N m⁻³ day⁻¹ in 2021 (with a halved dosing rate), compared to 1 g N m⁻³ day⁻¹ in the undosed bioreactor in 2018. Even under nitrate-limiting conditions, the added methanol was effectively removed in the bioreactor, with a mean removal rate of 106 g CH₃OH-C m⁻³ day⁻¹ . Methanol concentrations decreased by order of magnitude along the bioreactor (lengthwise) and never exceeded 50 mg CH₃OH-C L⁻¹ at the outflow. The added ca…
abstract: Several studies have demonstrated that denitrifying woodchips bioreactors effectively remove nitrate from a broad spectrum of wastewater. Even though bioreactors have a comparatively small spatial footprint and are straightforward to construct, the low long-term nitrate removal efficiency they provide compared to other mitigation options, such as constructed wetlands, may limit their utilization by catchment managers and landowners. This thesis investigated the use of external carbon dosing in bioreactors to improve nitrate removal and quantified some potential adverse effects of carbon dosing on bioreactors and downstream aquatic environments. Through observations ranging from field to mesocosm experiments, this thesis sought to (1) determine whether and to what extent external carbon dosing could improve nitrate removal in bioreactors and (2) assess the potential adverse effects of carbon dosing, such as reduced hydraulic performance and pollution swapping. The first component of the study evaluated the carbon dosing of a pilot-scale (58 m³) bioreactor treating drainage waters from a 0.65 ha paddock on a dairy farm. The effects of carbon dosing on the bioreactor's nitrate removal rates were assessed following a constant dosage of 8% (v/v) methanol solution at 10 mL min⁻¹ to the bioreactor's inlet distributor. Sulfate reduction and losses of added methanol from the bioreactor’s outlet were quantified as the potential adverse effects of external carbon dosing. Methanol dosing increased seasonal nitrate removal rates to 8 g N m⁻³ day⁻¹ in 2020 and 5 g N m⁻³ day⁻¹ in 2021 (with a halved dosing rate), compared to 1 g N m⁻³ day⁻¹ in the undosed bioreactor in 2018. Even under nitrate-limiting conditions, the added methanol was effectively removed in the bioreactor, with a mean removal rate of 106 g CH₃OH-C m⁻³ day⁻¹ . Methanol concentrations decreased by order of magnitude along the bioreactor (lengthwise) and never exceeded 50 mg CH₃OH-C L⁻¹ at the outflow. The added ca…
author: Moghaddam, Reza
keywords: Woodchip bioreactors, thesis with publication, Carbon dosing, Enhanced nitrate removal, Denitrification, Drainage waters
license: https://researchcommons.waikato.ac.nz/bitstreams/e01f4874-2b7f-4773-97f8-b65bd782dfae/download
date published: 2022
date modified: 2026-07-24T05:57:55Z
provider: University Waikato
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: The University of Waikato