This study aimed at evaluating the potential use of carbonated bauxite residue (CBR) as filter substrate to upgrade phosphorus (P) removal in small wastewater treatment plants such as constructed wetlands. Comparative experiments of P removal were performed in two columns continuously fed with synthetic and real wastewater to investigate the behavior of CBR under aerobic (column A) and anoxic biotic conditions (column B). The effect of various parameters, including pH, temperature, addition of organic carbon, and dissolved oxygen concentration, was investigated. Also, a series of chemical extractions was performed to elucidate the main mechanisms of P removal achieved by CBR. Over 140 days of operation, columns A and B showed a total P removal performance of 98.5% and 91.6%, thus reaching a total P removal capacity of 0.63 mg P/g CBR and 0.61 mg P/g CBR, respectively. The results indicate that 2 aeration conditions and microbial activity can significantly affect the performance of CBR filters. Under aerobic conditions, precipitation of CaP complexes appears to be the main mechanism leading to P removal. Under anoxic biotic conditions, microbially driven mobilization of Fe from CBR may provide Fe ions for Fe-P precipitation, but also it may lead to Fe release from the filters. This study provides crucial information to evaluate the potential use of CBR at different steps of the wastewater treatment process. Overall, the results indicate that the use of CBR filters is particularly suitable as a tertiary treatment step to remove P from effluents with low organic load under aerobic conditions.