Date

2017

Author

Çakırlar, Şükrü Burak

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Microalgae can remove nitrogen (N) and phosphorus (P) in domestic and industrial wastewaters, which cause eutrophication in rivers, lakes and seas. Microalgae have also been recognized as a promising alternative for carbon dioxide (CO2) sequestration from flue gas. However, it is necessary to design flexible and low-cost cultivation systems and, use suitable operating conditions to achieve enhanced biomass productivities and high CO2 fixation efficiencies. The aims of this study were: (i) to determine optimum hydraulic retention times (HRTs) for cultivation of microalgae in different types of wastewaters; (ii) to compare the microalgal productivities and nutrient removal rates at different N:P ratios (iii) to propose an integrated system for the utilization of wastewater and CO2 in flue gas for the production of microalgae. Within this context, a mixed microalgae culture collected from Araç Creek in Karabük Province in Turkey was grown under batch and semi-continuous operation modes. Two types of culture mediums were used in the experiments: (i) primary treated domestic wastewater from Ankara Tatlar WWTP and (ii) KARDEMIR Coke Plant wastewater diluted with supernatant of sludge thickener tanks of Ankara Tatlar WWTP. While ambient air (0.03% CO2) was supplied to the cultures grown with primary treated domestic wastewater, CO2 enriched air (4% CO2) was sparged into the cultures grown with diluted industrial wastewater. Light and mixing (aeration) conditions were the same in all set-ups. The optimum inoculum volume was determined as 10% (v/v) conducting a batch study and was used in all experiments. The optimum HRT was found to be 2 days for cultivation of microalgae in primary treated domestic wastewater. Mixed microalgae culture was able to remove 94.7% of Total Ammonia Nitrogen (TAN) and 93.8% of orthophosphate (PO4-P) from domestic wastewater at a HRT of 2 days. Although almost complete nutrient removal efficiencies were observed during steady conditions of the cultures with 4- and 8-day HRT, the steady-state conditions could not be maintained and cell washout was observed in the reactors due to nutrient limitation. The TAN/PO4-P (g/g) ratio of 6 resulted in the maximum nutrient removal efficiency when the diluted coke plant wastewater was used in the batch-mode operation. Results of the semi-continuous study conducted with diluted coke plant wastewater revealed that HRT should be kept 8 days at minimum in order to achieve efficient TAN and PO4-P removal (>98%) and high steady-state biomass concentrations (>2.4 mg TS/L). The CO2 removal rates were highest in the culture with 12 day-HRT and, it was obtained as 0.436 g CO2/h. The results demonstrated both effectiveness and potential application of the coupled system to remove nutrients from domestic and industrial wastewaters and simultaneous CO2 removal from a point source.  

Subject Keywords

Microalgae., Carbon dioxide., Sewage, Sewage

URI

http://etd.lib.metu.edu.tr/upload/12620946/index.pdf
https://hdl.handle.net/11511/26429

Collections

Graduate School of Natural and Applied Sciences, Thesis