The photosynthetic performance of a helical tubular photobioreactor ("Biocoil"), incorporating the filamentous cyanobacterium Spirulina platensis, was investigated. The photobioreactor was constructed in a cylindrical shape (0.9 m high) with a 0.25-m(2) basal area and a photostage comprising 60 m of transparent PVC tubing of 1.6-cm inner diameter (volume = 12.1 L). The inner surface of the cylinder (area = 1.32 m(2)) was illuminated with cool white fluorescent lamps; the energy input of photosynthetically active radiation (PAR, 400 to 700 nm) into the photobioreactor was 2920 kJ per day. An air-lift system incorporating 4% CO2 was used to circulate the growth medium in the tubing. The maximum productivity achieved in batch culture was 7.18 g dry biomass per day [0.51 g.d biomass/L.day, or 5.44 g.d biomass/m(2) (inner surface of cylindrical shape)/day] which corresponded to a photosynthetic (PAR) efficiency of 5.45%. The CO2 was efficiently removed from the gaseous stream; monitoring the CO2 in the outlet and inlet gas streams showed a 70% removal of CO2 from the inlet gas over an 8-h period with almost maximum growth rate.