Investigation of the growth and operational conditions for the enrichment of Chlorella vulgaris and its use in anaerobic digestate treatment

Subaşı, Irmak
Recently, microalgae have proved its prosperity in wastewater treatment technologies with high nutrient removal efficiency and robustness. Thus, the aim of this master thesis focused to investigate the optimum conditions for enrichment of Chlorella vulgaris under autotrophic and mixotrophic conditions and to research the treatment of anaerobic digestate with C. Vulgaris. In this thesis study, C. Vulgaris culture was first enriched under autotrophic conditions ammonium-N. The optimum illumination period of hourly frequencies (24h:0, 8h:8h:8h, 6h:6h:6h:6h, 12h:12h) were investigated in batch mode. This thesis is the first to investigate the effect of intermittent illumination in the literature with hourly illumination frequencies. The highest total ammonium nitrogen (TAN) (80%) and PO4-3-P (40%) removal efficiency and caratenoid production (800μg/mL) were obtained at 24h:0 (light:dark) illumination. Thereafter, the optimum N:P ratio (6,8,10) was investigated in semi-continuous photobioreactors (PBRs) with 8-day HRT. The highest TAN (almost 100%) and PO4-3-P (60%) removal efficiencies were obtained with N:P ratio of 8. C. Vulgaris culture was then enriched under mixotrophic conditions in batch PBRs. Then, the effect of 2-, 4- and 8- day HRT was investigated in semi-continuous PBRs. Accordingly, almost 100% TAN, 100% PO4-3- P and 50% sCOD removal efficiencies were obtained at 4-day HRT. Afterwards, the optimum Nitrogen Loading Rate (NLR) and Phosphorus Loading Rates (PLR) were investigated at constant HRT of 4 days and the almost 100% TAN, PO4 -3-P and 50% sCOD removal efficiencies were achieved, at NLR of 8 mg N/L.d, PLR of 1 mg P/L.d. and OLR of 100 mg/L.d sCOD Finally, mixotrophic C. Vulgaris culture enriched under optimum conditions defined above were used for the treatment of an anaerobic digestate containing chicken manure, poppy seeds, unpretreated and pretreated corncob. The microalgae-bacteria consortium exhibited almost 100% TAN, 80% PO4-3-P and 50% TOC removal efficiencies and an overall improvement in microalgal growth performance was observed. Results revealed that microalgal systems can be operated as complementary systems to anaerobic digesters to achieve further nutrient removal and create an opportunity of algal biomass for value-added products.


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Citation Formats
I. Subaşı, “Investigation of the growth and operational conditions for the enrichment of Chlorella vulgaris and its use in anaerobic digestate treatment,” M.S. - Master of Science, Middle East Technical University, 2022.