Newcastle University

Graduate Student, School of Civil Engineering and Geosciences

Thesis Title: Biogeochemical processes in a reducing and alkalinity producing system, Bowden Close, UK

Supervisors: Dr A P Jarvis
Prof A C Aplin

About

The European Water Framework Directive requires the treatment of acid mine water in order to prevent unfavourable effects on surface and groundwaters as well as on aquatic biota.
The treatment can either be accomplished actively or by passive treatment system. The latter option decreases metal loads and net acidity by natural chemical and microbial attenuation processes.

One of these passive treatment systems is Bowden Close consisting of two sequential Reducing and Alkalinity Producing Systems (RAPS) followed by an aerobic reed wetland.
The PTS is located 12 km southwest of Durham in the Northeast of the United Kingdom and aims to diminish iron and aluminium concentrations and raise pH by addition of alkalinity in the mine water to allow the discharge into a local burn.
Bowden Close has been commissioned in 2003 after positive outcomes of a pilot scale treatment system. Besides an extensive monitoring of the water quality of influents and effluents of Bowden Close since 2003, so far few geochemical analyses have been undertaken to identify its efficiency and leading (bio)geochemical processes involved in the treatment. However, only by understanding these, remediation can be fully assessed and lessons learnt for future projects of similar nature.

For this reason, the present research study focuses in first instance on the mass balance of major contaminants (Fe, Al, Mn, Zn and SO4) of the PTS to identify their seasonal removal behaviour and therewith asses the treatment efficiency of the passive treatment system.
Secondly, an intensive testwork will follow on sediment cores of the RAPS to identify:

-the total concentrations of sulphur, carbon and iron and their main mineral and organic species along with their spatial  distribution throughout the RAPS
-identify the degree of sulphur stable isotope fractionation caused by the treatment process to evaluate the importance bacterial sulphate reduction has on the treatment process
-the processes involved in the generation of alkalinity within the RAPS and the contribution that the dissolution of limestone and the anaerobic decay of organic matter have on the increase of pH in the mine water by filtering through the reactive compost-limestone substrate

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