Kinetic study on clogging of a geothermal pumping well triggered by mixing-induced biogeochemical reactions

Environmental Science & Technology
By: , and 

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Abstract

The sustainability of ground-source geothermal systems can be severely impacted by microbially mediated clogging processes. Biofouling of water wells by hydrous ferric oxide is a widespread problem. Although the mechanisms and critical environmental factors associated with clogging development are widely recognized, effects of mixing processes within the wells and time scales for clogging processes are not well characterized. Here we report insights from a joint hydrological, geochemical, and metagenomics characterization of a geothermal doublet in which hydrous ferric oxide and hydrous manganese oxide deposits had formed as a consequence of mixing shallow groundwater containing dissolved oxygen and nitrate with deeper, anoxic groundwater containing dissolved iron (FeII) and manganese (MnII). Metagenomics identify distinct bacteria consortia in the pumping well oxic and anoxic zones, including autotrophic iron-oxidizing bacteria. Batch mixing experiments and geochemical kinetics modeling of the associated reactions indicate that FeII and MnII oxidation are slow compared to the residence time of water in the pumping well; however, adsorption of FeII and MnII by accumulated hydrous ferric oxide and hydrous manganese oxide in the well bore and pump riser provides “infinite” time for surface-catalyzed oxidation and a convenient source of energy for iron-oxidizing bacteria, which colonize the surfaces and also catalyze oxidation. Thus, rapid clogging is caused by mixing-induced redox reactions and is exacerbated by microbial activity on accumulated hydrous oxide surfaces.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Kinetic study on clogging of a geothermal pumping well triggered by mixing-induced biogeochemical reactions
Series title Environmental Science & Technology
DOI 10.1021/acs.est.9b00453
Volume 53
Issue 10
Year Published 2019
Language English
Publisher American Chemical Society Publications
Contributing office(s) Pennsylvania Water Science Center
Description 10 p.
First page 5848
Last page 5857
Country France
City Orleans