INTERACTIVE EFFECT OF AMMONIA AND NITRATE ON THE NITROGEN UPTAKE BY Nannochloropsis sp.

Microalgae are able to assimilate various types of nitrogen. The interaction of nitrogen on their removal by microalgae should be of great concern when microalgae are used as a biological treatment in waste water. This study aims to reveal the preference of nitrogenous compounds by Nannochloropsis sp. The microalgae were cultivated in 900 μM nitrate, 900 μM ammonium, and 900 μM nitrate plus 900 μM ammonium. Nannochloropsis sp. preferred ammonium rather than nitrate when both compounds were available to the microalgae. Nitrate was utilised in the absence of ammonium. The uptake rate of ammonium was significantly higher than nitrate (p = 0.004). There was significant difference in the growth rate of the microalgal with different nitrogen sources (p < 0.000). Nannochloropsis sp. grew faster in treatment containing ammonia. However, there were no significant difference in the maximum cell density produced by the cultures in different nitrogenous nutrients (p = 0.224). Nannochloropsis sp. can be used as a biological treatment for waste water. The microalgae will first remove ammonium and remediate ammonia toxicity to most fish. Once ammonium has been removed or brought down to a safer level, nitrate can be removed by the microalgae.