A new photobioreactor design (110 l) for the biological production of hydrogen with the microalga Chlamydomonas reinhardtii is presented. The photobioreactor (PBR) was made up of 64 tubes (i.d., 27.5 mm, length, 2 m) arranged on an 8 x 8 square pitch cell connected by 64 U-bends for a total length of 133 m. The PBR was contained in a rectangular parallelepiped tank (2.5 x 2 x 2 m) made with isotactic polypropylene, except for the opposite square faces which were made of transparent Plexiglas. The tubes were immersed in a thermostatic water bath and continuously illuminated with artificial light. The culture was circulated with a peristaltic pump. To attain a uniform distribution of light to the cells, we used a suspension of silica nanoparticles that scattered the light supplied by the light bulbs (2 x 2000 W) from the opposite square sides of the photobioreactor. Growth experiments carried out with C. reinhardtii CC124 strain, showed a 23% net increase in the final chlorophyll concentration when the nanoparticle suspension was used. Hydrogen production with the C. reinhardtii strain CC124 was investigated with the new photobioreactor design and carried out using a direct inoculum of sulfur-limited cultures having a residual sulfate concentration below 1 mg l(-1). The mean hydrogen output was 3121.5 +/- 178.9 ml. The reactor fluid dynamic was investigated, and a tri-dimensional light profile inside the PBR is reported. Copyright (c) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.