This study explored the influence of azo dye concentration, salinity (with and without aeration) and nitrate concentration on bioelectricity generation and treatment performance in the up-flow constructed wetland-microbial fuel cell (UFCW-MFC) system. The decolourisation efficiencies were up to 91% for 500 mg/L of Acid Red 18 (AR18). However, the power density declined with the increment in azo dye concentration. The results suggest that the combination of salinity and aeration at an optimum level improved the power performance. The highest power density achieved was 8.67 mW/m(2). The increase of nitrate by 3-fold led to decrease in decolourisation and power density of the system. The findings revealed that the electron acceptors (AR18, nitrate and anode) competed at the anodic region for electrons and the electron transfer pathways would directly influence the treatment and power performance of UFCW-MFC. The planted UFCW-MFC significantly outweighed the plant-free control in power performance.