Nutrients recycle and the growth of <i>Scenedesmus obliquus</i> in synthetic wastewater under different sodium carbonate concentrations

Abstract

This study illustrated the growth of <i>Scenedesmus obliquus</i> and recycle of nutrients in wastewater combined with inorganic carbon under autotrophic conditions. <i>Scenedesmus obliquus</i> was cultivated under different conditions by adding sodium carbonate (Na₂CO₃) at 15-40 mg l^-1 separately in wastewater containing high nitrogen and phosphorus content. The growth characteristics of <i>S. obliquus</i>, pH and dissolved inorganic carbon (DIC) changes of microalgae liquid, the recycle rate of ammonia and phosphorus and lipid content were determined. The changes of pH and DIC showed that <i>S. obliquus</i> could use Na₂CO₃ to grow, with lipid contents of 18-25%. Among all Na₂CO₃ concentrations, 20 mg l^-1 was the optimum, of which <i>S. obliquus</i> had the highest NH₃-N recycle of 52% and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mtext>P</mml:mtext> <mml:msubsup><mml:mtext>O</mml:mtext> <mml:mn>4</mml:mn> <mml:mrow><mml:mn>3</mml:mn> <mml:mtext>-</mml:mtext></mml:mrow> </mml:msubsup> <mml:mtext>P</mml:mtext></mml:math> recycle of 67%. By the 14th day, its biomass production also reaches the maximum of 0.21 g l^-1. However, inorganic carbon fixation rate was inversely proportional to its concentration. Moreover, the biomass was in positive correlation with the Na₂CO₃ concentration except 20 mg l^-1, which provided a possibility that <i>S. obliquus</i> could be acclimatized to adjust to high concentrations of inorganic carbon to promote biomass accumulation and recycle of nutrients.