AbstractThis study was conducted to check the impact of plant roots on the treatment efficiency and hydraulic behavior of a vermifilter for synthetic dairy wastewater. Two horizontal subsurface flow (HSSF) vermifilters, one with plants (MAVF) and the other without plants (VF), were used for this study. The experiment was conducted with a hydraulic loading rate of 1.5 m3/m2·day using the Eisenia fetida earthworm and Canna indica wetland plant. The average COD removal from HSSF-MAVF and HSSF-VF was 75 ± 5.7% and 64 ± 3.83%, respectively. The average total nitrogen removal for HSSF-MAVF and HSSF-VF was 44 ± 4.4% and 35.5 ± 3%, respectively, whereas the average total phosphorus removal from HSSF-MAVF and HSSF-VF was 57 ± 3.4% and 51 ± 2.8%, respectively. The activity of plant roots in HSSF-MAVF was observed to considerably delay clogging in HSSF-VF. The overall bed media porosity reduction was more in HSSF-MAVF (33%) than in HSSF-VF (28%). However, the impact of plant roots on bed media clogging was comparatively very marginal, leading to only 5%–6% additional porosity reduction over HSSF-VF. The characteristics of clog matter (CM) were composed of both organic and inorganic matter. Organic components such as protein, polysaccharides, nucleic acids, and humic acids were observed in both the reactor beds.