Study of the Growth Parameters of the Nannochloropsis Oculata for the Nitrogen and Phosphorus Removal from Wastewater through Design of Experiment Approach

Microalgae are a promising renewable energy source because of their capability to produce a large amount of oil, which can be directly used as a fuel or converted into biodiesel through transesterification processes. Microalgae growth needs a certain amount of nutrients such as nitrogen and phosphorus and, with this regard, the wastewater arising from aquaculture and many others agro-industrial processes can be a suitable and cheap source of these elements. Moreover, nitrogen and phosphorus are responsible for the eutrophication of the waters basins, therefore microalgae can be proficiently used to remove these pollutants. In this work Nannochloropsis oculata was tested to verify the nitrogen removal capability from a synthetic wastewater. The medium was composed of marine water added with appropriate macro and micronutrients mixtures. The experiments were carried out by means of lab-scale, completely mixed bubble-columns, photo-bioreactors. A Design of Experiments (DoE) approach was here used in order to assess whether the input factors (i) light intensity, (ii) different nitrogen concentration sources and (iii) carbon dioxide have a statistically significant impact on the microalgae growth. It was demonstrated that the only factors statistically significant are the light intensity and its interaction with the nitrate concentration, at least for the parameter ranges here investigated. As a final remark, it was found that nitrate removal were completed from 3 to 5 days depending on the medium composition, whereas urea and phosphates needed more time.