Exploring the technical and economic feasibility of biological oxidation-filtration technology for treating South African groundwater with high concentrations of iron and manganese

Petrie, Daniel

Exploring the technical and economic feasibility of biological oxidation-filtration technology for treating South African groundwater with high concentrations of iron and manganese

Thesis / Dissertation

2026

Publisher

University of Cape Town

Department

Department of Civil Engineering

Faculty

Faculty of Engineering and the Built Environment

Abstract

Many water-stressed cities around the world are considering groundwater schemes as one way to secure drinking water supply to their residents. In South Africa, some of the most high-yielding groundwater sources contain elevated levels of dissolved minerals such as iron and manganese that need to be removed to meet the chronic health and aesthetic limits set by the national drinking water standard (SANS 241). For these schemes to be feasible, the proposed treatment plants need to be reliable and affordable. Historically, typical iron and manganese removal processes relied on aeration, dosing expensive oxidising chemicals and removing precipitated iron and manganese oxide particles by sedimentation and filtration at slow filtration rates (requiring many, or large, filters). These systems also generate precipitates that are difficult to dewater making residuals handling complicated and expensive. Over the past thirty years, interest in biological oxidation-filtration processes for removing iron and manganese has grown (driven by reported gains in process efficiency and affordability: needing smaller filters, fewer chemicals and producing residuals that are easier to dewater), but most applications globally have been for groundwater with more dilute concentrations than experienced in South Africa. There is also little agreement on appropriate design criteria (filtration rates, pH/OxidationReduction Potential conditions) for such biological processes. This research aimed to test the technical and economic feasibility of biological oxidation-filtration technology for removing high concentrations of iron (up to 7.5 mgFe/ℓ) and manganese (up to 2.5 mg/ℓ) from groundwater. It also aimed to test what operating parameters could be optimised during design and operation of municipal scale biofiltration plants. Experiments were conducted over 8 days at a live municipal-scale biofiltration plant (the newly commissioned Coegakop water treatment works in Gqeberha, Eastern Cape) to prove effective removal of iron and manganese and to measure removal efficiencies at different residence times/filtration rates, different influent concentrations, different pH-ORP conditions, and different temperatures. The experimental results confirmed that the minerals are oxidised in the filter bed (without addition of oxidising chemicals) and removed to within target limits, although at slower filtration rates than claimed by other case studies. These results also confirmed that Coegakop is currently one of the largest biological manganese removal plants in the world. An economic analysis showed that biological oxidation-filtration technology is more affordable (33% lower on 20-year NPV costs) than conventional chemical oxidation-sedimentation-filtration technology – driven mostly by savings on capital expenses (smaller filters) and chemical dosing costs (avoiding oxidising chemicals). A sensitivity analysis confirmed that this preference holds regardless of ±50% variation to most input assumptions. This study opens the door for biological oxidation-filtration technology to be justifiably considered for new groundwater schemes that need to treat high concentrations of iron and manganese, and gives useful insights into the key drivers for technical and economic feasibility.

Keywords

Water Quality Engineering

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