J. Algal Biomass Utln. 2015, 6 (4): 1- 11 Growth of Arthrospira platensis in simple floating photobiorector ISSN: 2229 – 6905 1 1 The effect of different nitrogen sources on continuous growth of Arthrospira platensis in simple floating photobiorector design in outdoor conditions Norsalwani Muhamad Nor a , Mohamed Amar Naqqiuddin a , Nurshazreen Mashor a , Shahrizim Zulkifly a , Hishamuddin Omar a & Ahmad Ismail a* a Biology Department, Faculty of Science, University Putra Malaysia 43400, Serdang, Selangor. *Correspondent author, Email: aismail@upm.edu.my ___________________________________________________________________________________________________ Norsalwani Muhamad Nor, Mohamed Amar Naqqiuddin, Nurshazreen Mashor, Shahrizim Zulkifly, Hishamuddin Omar andAhmad Ismail. 2015. The effect of different nitrogen sources on continuous growth of Arthrospira platensis in simple floating photobiorector design in outdoor conditions. J. Algal Biomass Utiln., 6 (4): Keywords: Arthrospira platensis, variable weather, floating photobioreactor, fertilizer, nitrogen source Abstract Malaysia rests in the tropic region where cloud covers and rains make it less favorable for outdoor Arthrospira platensis (Spirulina) cultivation. That is the most likely reason why there is no commercial Spirulina cultivation in Malaysia. Therefore the aim of this study is to find out whether Spirulina can be cultured in simple photobioreactor floating in water body. A. platensis was cultivated in simple water based floating photobioreactor and land based tank using different composition of nitrogen sources (Urea and Ammonium Nitrate). Experiment was conducted in outdoor conditions to assess the respond of different nitrogen sources on the cell density, dry biomass and total chlorophyll of Spirulina gained in simple photobioreactors in actual variable culture conditions. Results showed significantly higher biomass dry weight (g L -1 ) with ammonium nitrate treated Spirulina under dry weather conditions for land based tank and water based photobioreactor at 3.026±0.058 and 4.687±0.154 respectively. Overall, productivity (g L -1 d -1 ) and specific growth rate (μ d -1 ) of Spirulina was highest with ammonium nitrate than urea for every cycles and photobioreactors under different weather patterns (wet, dry and mix). With current price of ammonium nitrate cheaper than urea suggesting that Spirulina can be cultured at lower cost in variable weather conditions such as Malaysia. Introduction Spirulina (Arthrospira platensis) has gained huge popularity for its benefits, having high protein contents, anti-oxidants, vitamins and other high nutritional values. With steady increase in human population, the demand for this unique cyanobacterium, Spirulina has been greater than before (Morist et al., 2001). However the price of Spirulina is still unaffordable for most people. In order to reduce the current market price of Spirulina, alternative nutrient sources were studied and investigated to replace expensive chemical fertilizers that have been used often in laboratory scale. Agricultural, industrial or domestic wastewaters have been proven beneficial for growing microalgae at commercial stage as these wastewaters have loads of essential nutrients that can be alternatively used as fertilizer sources. In addition to these implementations, removal or remediation of excess nutrient elements from wastewaters could also decrease impact to the environment (Metcalf, 2003). Efforts to reduce cultivation cost using cheap fertilizer composition have been reported by substituting ammonium phosphate (De et al., 1999), urea (Danesi et al., 2002), ammonium salts (Carvalho et al., 2004) and ammonium chloride (Bezerra et al., 2007) as appropriate nitrogen sources which resulted better growth of A. platensis. In Malaysia with frequent rain and