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Development of Multiple Processes to Cultivate Phagotrophic Algae with Wastewater Organics and Waste Activated Sludge

Li, Cong
http://rave.ohiolink.edu/etdc/view?acc_num=akron1435586707

Abstract Details

2015, Doctor of Philosophy, University of Akron, Chemical Engineering.
Sustainable and economical feedstock supply is critical to biofuel production. Currently, oil crops are the main source of biofuel feedstock. The situation has aroused sustainability concern because the use of oil crops for biofuel competes with food production for arable land use or, in some cases, encourages deforestation. Cultivation of photosynthetic algae for lipids has been pursued as popular alternative. While requiring little arable land, this approach is facing serious obstacles, particularly the limited depth of light penetration owing to the self-shading effect of algae cells themselves. The primary purpose of this research work is to develop sustainable, economical and environmentally friendly processes of cultivating phagotrophic algae with wastewater organics and waste activated sludge as biofuel feedstock. Firstly, a two-stage batch process was developed to cultivate phagotrophic algae with wastewater organics. In this two-stage batch process, wastewater was first treated with bacteria to deprive one or several essential nutrient(s) and convert partial wastewater organics into bacterial biomass. Then the grown bacteria together with the essential nutrient(s)-depleted wastewater were fed to phagotrophic algae for growth. The results demonstrate that phagotrophic algae can be successfully cultivated with wastewater organics through this process. About 22.1% of the wastewater organics were converted into algal biomass. The lipid content of the produced biomass was about 33.8% by weight. Then, a two-stage continuous process was developed to cultivate phagotrophic algae with wastewater organics. Compared to batch processes, continuous processes are more favorable in wastewater treatment plant owing to the higher efficiency and stability. In this continuous process, the wastewater was first pumped into a Bacteria Tank, where small bacteria grew by utilizing the wastewater organics and consumed out one or several essential nutrient(s). Then the grown bacteria together with the essential nutrient(s)-deficient wastewater were fed to phagotrophic algae. Phagotrophic algae can grow by obtaining the essential nutrient(s) from bacteria, whereas other microorganisms were severely inhibited for lacking of the essential nutrient(s). The feasibility of cultivating phagotrophic algae through this continuous process was investigated and the operation conditions such as dilution rate, pH, and DO were optimized. The results show that phagotrophic algae can be established as the dominant population by the built-in selection pressure of this continuous process without costly chemical/physical sterilization, which make this approach economically feasible. About 23% and 7% of the wastewater organics were converted into algal biomass and lipids respectively. The fatty acid methyl ester (major biodiesel components) yield from the produced lipids was about 33%. Next, a batch process of cultivating phagotrophic algae with waste activated sludge (WAS) was developed. WAS is the byproduct of current sewage wastewater treatment process. By feeding WAS directly to phagotrophic algae, the phagotrophic microalgae cultivation process can be readily incorporated into current wastewater treatment process without changing the facilities and operation of current wastewater plant. The batch process consists of two stages: short anaerobic digestion followed by algae-enhanced aerobic digestion. In the first stage, short anaerobic digestion was utilized to loosen WAS flocs and release organics out of flocs. In the second stage, phagotrophic algae consumed both the dissolved and small ingestible solid organics in the anaerobically pretreated WAS. The results showed that 36% of WAS suspended volatile-solids reduction and 28% of WAS total volatile-solids reduction were achieved in 96 h, with 72 h anaerobic digestion and 24 h algal-enhanced aerobic digestion. About 41% of the reduced WAS total volatile-solids were converted into algal biomass and the lipid content of the produced algal biomass was around 49% by weight. Lastly, strong alkali (NaOH) was utilized to treat WAS before feeding WAS to phagotrophic algae. Compared to short time anaerobic digestion, strong alkali is more effective and faster in loosening WAS flocs and releasing organics out of flocs. Firstly, alkali treatment at different pH and treatment time was evaluated and optimized (at pH 10 for 6 h) to release microbial cells and other organics from the WAS flocs. Then the alkali-treated WAS was fed to phagotrophic algae. In later experiments, the addition of small amounts of readily consumable organics, such as waste ketchup (WK), was found to enhance the percentage reduction of WAS organics and algae yield. With WK addition at 0.118:1 (w/w) WK-to-WAS organics, 46-49% of the WAS organic matter was digested within 16 h. The lipid content was 20.8% in the treated biosolids, increased from 6.8% in the original WAS. After the alkali treatment and algal growth, WAS can be processed into Class B biosolids by aerobic digestion within one day, much faster than the WAS without any algal treatment (about 7 days). With the fast WAS organics reduction rate and high lipid production ability, this process shows strong potential in both WAS digestion and biofuel production. In summation, multiple processes have been developed to cultivate phagotrophic algae with waste organics. All these processes demonstrate benefits in algae cultivation and waste treatment. The produced algal cells, which are rich in lipids, are good sources for biofuel production. By converting waste organics into algal biomass, the waste treatment becomes environment-friendly and sustainable in material recycling. Furthermore, with the costs shared by dual function for biofuel production and waste treatment, these processes are expected to have very favorable overall economics.
Lu-Kwang Ju, Dr. (Advisor)
Christopher M Miller, Dr. (Committee Member)
John M. Senko, Dr. (Committee Member)
Gang Cheng, Dr. (Committee Member)
Lingyun Liu, Dr. (Committee Member)
181 p.
Chemical Engineering

Recommended Citations

Citations

  • Li, C. (2015). Development of Multiple Processes to Cultivate Phagotrophic Algae with Wastewater Organics and Waste Activated Sludge [Doctoral dissertation, University of Akron]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=akron1435586707

    APA Style (7th edition)

  • Li, Cong. Development of Multiple Processes to Cultivate Phagotrophic Algae with Wastewater Organics and Waste Activated Sludge. 2015. University of Akron, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=akron1435586707.

    MLA Style (8th edition)

  • Li, Cong. "Development of Multiple Processes to Cultivate Phagotrophic Algae with Wastewater Organics and Waste Activated Sludge." Doctoral dissertation, University of Akron, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=akron1435586707

    Chicago Manual of Style (17th edition)

akron1435586707
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© 2015, some rights reserved.Creative Commons License Development of Multiple Processes to Cultivate Phagotrophic Algae with Wastewater Organics and Waste Activated Sludge by Cong Li is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License. Based on a work at etd.ohiolink.edu.
This open access ETD is published by University of Akron and OhioLINK.