Removal of Organic micropollutants (OMPs) with Subsurface Iron Removal (SIR)

Abstract

This research explores the potential effect of Subsurface Iron removal (SIR) on the removal of organic micropollutants (OMPs). The presence of OMPs and their transformation products in the water environments globally, have raised concerns due to the potential environmental and human health risks they are posing. Recent technologies often fail to remove OMPs completely or require high energy levels and costs. Previous findings by Vitens water company have indicated that SIR application resulted in the attenuation of certain OMPs. Therefore, the effect of SIR as an alternative, cost-effective removal method of OMPs was investigated.

A continuous flow column experiment was conducted in order to simulate the processes which take place under oxic conditions at SIR for the removal of 5 targeted OMPs (bentazone, metformin, caffeine, carbamazepine and atrazine). Two columns were filled with iron oxides (FeOx) coated sand and manganese oxides (MnOx) coated sand respectively, in order to simulate the two precipitation zones created in the subsurface. The aim of the study was to investigate the removal efficiencies of the selected OMPs in both columns in order to understand if the SIR environment is favourable for the
removal of OMPs.

Results indicated that for most compounds there was removal observed after 65 pore volumes of continuous flow. Metformin was hardly removed (<10% removal rate) in both materials. A higher removal efficiency was observed at the FeOx column for bentazone (65%), caffeine (54%) and carbamazepine (29%), while atrazine was the only compound which had a greater affinity for MnOx, with a removal rate of 87%.

These findings suggest that SIR has a potential on the removal of certain OMPs. It is suggested that during SIR the OMPs existing in the subsurface, pass through the two precipitation zones and undergo removal processes within both zones. However, based on their respective affinities to each of these zones, their removal extents vary accordingly. Ultimately, the water extracted from the undergoing SIR exhibits a reduced concentration of OMPs, which is a result of the combined removal mechanisms operating within both precipitation zones.