Semicontinuous cultures of Scenedesmus obliquus in artificial wastewater were maintained with 30% and 40% daily dilutions and under a 14: 10 h light-dark cycle, with temperatures of 25.5 and 17 degreesC during light and dark hours. Under this regime, the production of organic biomass was 39.3 and 25.2 mg l(-1) d(-1) for the 30% and 40% dilutions, and 24.9 and 16.7 mg l(-1) d(-1) of single-cell proteins. Most of the nitrogen removal took place during the light hours, with daily totals of 9.27 and 8.45 mg l(-1) for the 30% and 40% dilutions. With the former, 43.7% of the nitrogen removed was recycled by the microalgae into proteins and other organic nitrogen cell contents, but this efficiency decreased to 26.4% when the dilutions were raised to 40%. (C) 2004 Elsevier Ltd. All rights reserved.