CO2-assisted removal of nutrients from municipal wastewater by microalgae Chlorella vulgaris and Scenedesmus obliquus

Axenic culture of microalgae Chlorella vulgaris ATCC((R)) 13482 and Scenedesmus obliquus FACHB 417 was used for phycoremediation of primary municipal wastewater. The main aim of this study was to measure the effects of normal air and CO2-augmented air on the removal efficacy of nutrients (ammonia N and phosphate P) from municipal wastewater by the two microalgae. Batch experiments were carried out in cylindrical glass bottles of 1L working volume at 25 degrees C and cool fluorescent light of 6500lux maintaining 14/10h of light/dark cycle with normal air supplied at 0.2Lmin(-1) per liter of the liquid for both algal strains for the experimental period. In the next set of experiments, the treatment process was enhanced by using 1, 2 and 5% CO2/air (vol./vol.) supply into microalgal cultures. The enrichment of inlet air with CO2 was found to be beneficial. The maximum removal of 76.3 and 76% COD, 94.2 and 92.6% ammonia, and 94.8 and 93.1% phosphate after a period of 10days was reported for C. vulgaris and S. obliquus, respectively, with 5% CO2/air supply. Comparing the two microalgae, maximum removal rates of ammonia and phosphate by C. vulgaris were 4.12 and 1.75mgL(-1)day(-1), respectively, at 5% CO2/air supply. From kinetic study data, it was found that the specific rates of phosphate utilization (q(phsophate)) by C. vulgaris and S. obliquus at 5% CO2/air supply were 1.98 and 2.11day(-1), respectively. Scale-up estimation of a reactor removing phosphate (the criteria pollutant) from 50 MLD wastewater influent was also done.