Enhanced removal of organic micropollutants in earthworm-assisted sludge treatment reed beds

This study examines organic micropollutants (OMPs) behavior in sludge treatment reed beds (STRBs), focusing on the first evaluation of Eisenia fetida and Arundo donax in OMP retention and reduction. A pilot-scale STRB with different treatments was operated for one year, reporting the occurrence of 66 OMPs in sludge and drained water, 8 of which were found in both solid and liquid phases. Significant seasonal dynamics in OMP were observed, with higher levels in the dry season. Among OMPs, citalopram exhibited the highest concentration (67 µg/g_DS) during the dry season, whereas BAC-C12 reached 22 µg/g_DS during the wet season in the feeding sludge. Earthworms and Arundo donax were associated with significant reductions in OMPs in the residual sludge, with the average decrease of 53 % (particularly in the top sludge layers). In the presence of earthworms, the concentrations of citalopram and amisulpride in the drained water were 74 % and 90 % lower compared to the control units, respectively. The final resting phase further enhanced the stabilization of the OMPs in the residual sludge in the top layers, with significant reductions observed for compounds like caffeine (66 %) and losartan (99 %). However, compounds such as amisulpride and citalopram showed minimal reduction in the resting phase. A risk quotient (RQ) assessment for selected terrestrial organisms indicated consistently low environmental risks (RQ<1) across all treatments in the case of sludge reuse. Overall, the STRB assisted with earthworms and Arundo donax retained and reduced OMPs, although some persisted, highlighting STRB technology as a sustainable, nature-based solution for sludge reuse.