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Sustainable Cultivation of Microalgae Using Diluted Anaerobic Digestate for Biofuels Production

Abu Hajar, Husam A.
http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1470932526

Abstract Details

2016, Doctor of Philosophy (PhD), Ohio University, Civil Engineering (Engineering and Technology).
Microalgae cultivation has gained considerable interest recently as a potential source for the production of biofuels. Nevertheless, many obstacles still face the industrial application of microalgal biofuels such as the high production costs due to nutrient requirements and the high energy input for cultivating and harvesting the microalgal biomass. In this study, the utilization of the anaerobic digestate as a nutrient medium for the cultivation of two microalgal species was investigated. The anaerobic digestate was initially characterized and several pretreatment methods such as hydrogen peroxide treatment, filtration using polyester filter bags, and supernatant extraction were applied to the digestate. It was found that the supernatant extraction was the simplest and most effective method in decreasing the turbidity and COD of the diluted anaerobic digestate while maintaining sufficient nutrients (particularly nitrogen) for microalgae cultivation. The microalga Neochloris oleoabundans was cultivated using the diluted anaerobic digestate supernatant on a bench-scale. It was found that 100 mg N/L dilution was sufficient to maximize the biomass concentration of this microalga. It was attempted to scale up the cultivation of the microalga N. oleoabundans to 100 L raceway ponds; however, the culture was contaminated with other algal species. The microalga Scenedesmus dimorphus was then cultivated using the anaerobic digestate supernatant on a bench-scale. The highest biomass concentration recorded was 654 mg/L. Furthermore, it was found that 50 – 100 mg N/L dilutions were sufficient to maximize the specific growth rate of this microalga while still producing relatively high biomass concentrations. As a result, the microalgae cultivation was scaled up to 100 L raceway ponds using 100 mg N/L dilution at 454 and 317 µmol/m2/s light intensities and 50 mg N/L dilution at 384 and 234 µmol/m2/s light intensities. The highest biomass concentration achieved was 432 mg/L in the 100 mg N/L – 454 µmol/m2/s culture. Nitrogen removal efficiencies were in the 65 – 72% range with complete ammonia removal. Phosphorus removal efficiencies were in the 63 – 100% range while COD removal efficiencies as a result of the bacteria presence in the unsterilized nutrient media were in the 78 – 82% range. The effect of mixing on the growth of the microalga S. dimorphus was evaluated by cultivating this microalga in a raceway pond at 0.1, 0.2, and 0.3 m/s water surface velocities. It was concluded that the biomass concentration and growth rate increased with an increase in the mixing velocity. However, by balancing the power required to operate the pond at different velocities with the potential energy yield from biodiesel synthesis, it was found that operating the pond at 0.1 m/s surface velocity was the only case with a positive net energy. Finally, two biomass growth models were developed and tested on the growth of the microalga S. dimorphus. It was found that the logistic model, which assumes a maximum bearing capacity of the culture, represented the biomass growth better than the exponential growth model, which assumes that the microalgae grow exponentially at specific growth rates equal to or less than the maximum specific growth rate depending on the culture conditions.
R. Guy Riefler (Advisor)
223 p.
Civil Engineering; Environmental Engineering
Microalgae; Anaerobic digestion; Sustainable housing; Modeling; Biofuels; Acid mine drainage

Recommended Citations

Citations

  • Abu Hajar, H. A. (2016). Sustainable Cultivation of Microalgae Using Diluted Anaerobic Digestate for Biofuels Production [Doctoral dissertation, Ohio University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1470932526

    APA Style (7th edition)

  • Abu Hajar, Husam. Sustainable Cultivation of Microalgae Using Diluted Anaerobic Digestate for Biofuels Production. 2016. Ohio University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1470932526.

    MLA Style (8th edition)

  • Abu Hajar, Husam. "Sustainable Cultivation of Microalgae Using Diluted Anaerobic Digestate for Biofuels Production." Doctoral dissertation, Ohio University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1470932526

    Chicago Manual of Style (17th edition)

ohiou1470932526
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© 2016, all rights reserved.
This open access ETD is published by Ohio University and OhioLINK.