Integrated carbon dioxide mitigation and nutrient removal from municipal and industrial wastewater using microalgal systems

Thesis Type: Postgraduate

Institution Of The Thesis: Middle East Technical University, Faculty of Engineering, Department of Environmental Engineering, Turkey

Approval Date: 2017

Thesis Language: English


Principal Consultant (For Co-Consultant Theses): Tuba Hande Bayramoğlu

Co-Consultant: Sibel Uludağ Demirer


The aim of this master thesis study is to investigate the nutrient removal efficiency from different kinds of wastewaters and the carbon dioxide mitigation in photobioreactors with unialgal culture, Chlorella vulgaris. In the first part of the study, Chlorella vulgaris culture was cultivated in the Bold’s basal medium in batch reactors to increase the biomass content and to observe the growth phases of alga. Then, two parallel photobioreactors (PBRs) were run to cultivate Chlorella vulgaris culture semi-continuously to determine the minimum control requirements on the system to achieve steady-state. pH control at every feeding procedure and temperature regulation requirements became evident. Secondly, nutrient removal from municipal wastewater by Chlorella vulgaris was investigated. Three PBRs were operated at 2, 4 and 8 days of hydraulic retention time (HRT) in semi-continuous PBRs to determine the optimum HRT to achieve the highest nutrient removal. At the 4 day of HRT, 98-100% total ammonium nitrogen (TAN) and 85-98% ortho-phosphate (PO4-P) removal efficiencies were achieved, which was the highest removal among all other HRTs. Before and after the semi-continuous set of experiments, batch sets were run with unacclimated and acclimated algal culture. The highest biomass growth rates of the cultures were measured as 0.39 d-1 for unacclimated and 0.82 d-1 for acclimated culture showing that acclimation is important for system efficiency. At the final part, it was aimed to treat coke factory wastewater, which was mixed with supernatant of primary sludge thickener (thickener supernatant) to provide phosphorus and dilution to the system by supplying 4% carbon dioxide (CO2)-enriched air with Chlorella vulgaris. Mixing ratio of two wastewaters was determined by set of batch experiments to identify the optimum nitrogen: phosphorous (N/P) ratio for Chlorella vulgaris. After this ratio was determined as 6, semi-continuous set of experiments were done with mixed wastewater prepared accordingly. Among 3 HRTs studied (5, 8, and 12 days), 12 days of HRT provided the best removal rates as 97.5% TAN, 97% PO4-P, and 17.7 % CO2 removal. Outcomes of this thesis study can be further used for large scale experimental sets to treat that specific wastewaters with Chlorella vulgaris.