Twenty years of Italian outdoor investigations on closed photobioreactors are discussed in this review. Many
photobioreactor designs have been projected; some have been built, tested and patented. The Italian research approach
from tubular (single tube and traditional loop) to flat and column and again to tubular photobioreactors (coil and loops)
has improved microalgal yield. It increased from 25.0 gm-2d-1 in 1986 (using a traditional loop set down on the ground) to
47.7 gm-2d-1 in 2003, when results of a new tubular undulating row photobioreactor (TURP) were reported. This very high
TURP productivity was attributed to a light dilution growth-strategy using Arthrospira platensis; the photic ratio (Rf)
ranged from 3 to 6.