**3. Conclusion**

Production of microalgal at large scale is needs high giant investment and operational prices. The use of open ponds, like raceway ones, may be cheaper to create and operate than other methods, but need giant land area. On the other hand, the restrictions condition for operation of open ponds, such as high condition for temperature limitations, and light intensity, it's value lead to accentuate the efforts in developing outside PBRs. Many research has been done to develop PBRs for protects cultures from contamination, enhance PBRs technologies and enhance mass production. Also, from the economical PBRs view point, the major concerns developing new design of PBRs model have clear and high illumination surface, thus use low energy input and utilizing maximal solar energy. The good PBR models, should be possess high mass transfer rates and high biomass yields within short time of incubation. Other factors like sort of strain, the target product, geographical location, and cost of production are required.
