Temperature and flow velocity dependency of biological screen-slot clogging in injection wells

Abstract Biological clogging in injection wells for ground water heat pump (GWHP) systems presents a significant operational challenge. The initial stage of clogging involves bacterial fouling attaching to the screen slots of the well pipes. However, few studies have systematically investigated its proliferation under different coupled conditions of injection water temperatures and horizontal groundwater flows. This study conducted a tank experiment to measure fouling weights on inserted steel plates under various test conditions involving two factors. Untreated groundwater from the bottom was supplied, and groundwater with adjusted temperature and dissolved oxygen from the top was introduced. The mass increase of iron-oxidation biofouling on the slotted steel plates was measured under varying conditions of injection water temperature and flow velocity through the slots. Results showed that higher flow velocities and elevated injection water temperatures increased biofouling mass. Specifically, the mass increased by up to 1.6 times due to differences in flow velocity and by up to 2.7 times due to differences in injection temperature. These results indicate that iron-oxidizing bacteria are activated by rising injection temperatures, as corroborated by previous studies, and that faster flow velocities provide a greater supply of substrates in the groundwater. Finally, the relationship between biofouling mass and injection temperatures was analyzed using an Arrhenius plot. This analysis yielded apparent activation energy values of 62.6 kJ/mol at a flow velocity of 1 m/d and 54.5 kJ/mol at a flow velocity of 0.1 m/d, with respective determination coefficients of 0.94 and 0.95.