Kinetic study of nutrients removal from municipal wastewater by Chlorella vulgaris in photobioreactor supplied with CO₂-enriched air

The microalgae Chlorella vulgaris ATCC 13482 was used in the present study for municipal wastewater treatment. Batch experiments were performed in bubble column photobioreactors of 7 L working volume maintained at 25 ± 2°C and 14 h/10 h of photo and dark cycle. The treatment process was enhanced by using CO₂-augmented air (5% CO₂ v/v) supply into the microalgal culture in comparison to the use of normal air (0.03% CO₂ v/v). For a period of 7 days, C. vulgaris effected maximum removals of 74.4% soluble fraction of chemical oxygen demand, 72% ammonia (NH₄–N), 60% nitrate (NO₃–N) and 81.93% orthophosphate (PO₄–P) with use of normal air, whereas 84.6% sCOD, 88% NH₄–N, 72% NO₃–N and 92.8% PO₄–P removals, respectively, with use of 5% CO₂/air supply. Using kinetic study data, the specific rates of ammonia and phosphate uptake (q_ammonia and q_phosphate) by C. vulgaris at 5% CO₂/air supply were found to be 2.41 and 0.85 d⁻¹, respectively. Using the algal remediation technology, nitrogen–phosphorus–potassium recovery from sewage treatment plant of 37.5 million litres per day wastewater influent capacity was calculated to be ∼298.5, 55.4 and 83.7 kg d⁻¹, respectively.