This study investigated the photoperiodic effects on the biomass production and nutrient removal in the algal-bacterial wastewater treatment, under the following three conditions: (1) a natural 12 h: 12 h LD cycle, (2) a dark-elongated 12 h: 60 h LD cycle, and (3) a two-phase photoperiodic 12 h: 60 h LD, followed by 12 h: 12 h LD cycles. The two-phase photoperiodic operation showed the highest dry cell weight and lipid productivity (282.6 mg L (1) day (1), 71.4 mg L (1) day (1)) and most efficient nutrient removals (92.3% COD, 95.8% TN, 98.1% TP). The genetic markers and sequencing analyses indicated rapid increments of bacteria, subsequent growths of Scenedesmus, and stabilized population balances between algae and bacteria. In addition, the two-phase photoperiod provided a higher potential for the algal-bacterial consortia to utilize various organic carbon substrates. (C) 2015 Elsevier Ltd. All rights reserved.