Matching Items (4)
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- All Subjects: Microalgae
- Creators: Torres, César I
Description
The application of microalgal biofilms in wastewater treatment has great advantages such as abolishing the need for energy intensive aerators and recovering nutrients as energy, thus reducing the energy requirement of wastewater treatment several-fold. A 162 cm2 algal biofilm reactor with good wastewater treatment performance and a regular harvesting procedure was studied at lab scale to gain an understanding of effectual parameters such as hydraulic retention time (HRT; 2.6 and 1.3 hrs), liquid level (LL; 0.5 and 1.0 cm), and solids retention time (SRT; 3 and 1.5 wks). A revised synthetic wastewater “Syntho 3.7” was used as a surrogate of domestic primary effluent for nutrient concentration consistency in the feed lines. In the base case (2.6 hr HRT, 0.5 cm LL, and 3 wk SRT), percent removals of 69 ± 2 for total nitrogen (TN), 54 ± 21 for total phosphorous (TP), and 60 ± 7 for chemical oxygen demand (COD) were achieved and 4.0 ± 1.6 g/m2/d dry biomass was produced. A diffusion limitation was encountered when increasing the liquid level, while the potential to further decrease the HRT remains. Nonlinear growth kinetics was observed in comparing SRT variations, and promoting autotrophic growth seems possible. Future work will look towards producing a mathematical model and further testing the aptness of this system for large-scale implementation.
ContributorsHalloum, Ibrahim (Author) / Torres, César I (Thesis advisor) / Popat, Sudeep C (Committee member) / Rittmann, Bruce E. (Committee member) / Arizona State University (Publisher)
Created2016
Description
The aims of this project are to demonstrate the design and implementation of separations modalities for 1) in situ product recovery and 2) upstream pretreatment of toxic feedstocks. Many value-added bioproducts such as alcohols (ethanol and butanol) developed for the transportation sector are known to be integral to a sustainable future. Likewise, bioproduced aromatic building blocks for sustainable manufacturing such as phenol will be equally important. The production of these compounds is often limited by product toxicity at 2- 20 g/L, whereas it may desirable to produce 20-200 g/L for economically feasible scale up. While low-cost feedstocks are desirable for economical production, they contain highly cytotoxic value-added byproducts such as furfural. It is therefore desirable to design facile detoxification methods for lignocellulose-derived feedstocks to isolate and recover furfural preceding ethanol fermentation by Escherichia coli. Correspondingly it is desirable to design efficient facile in situ recovery modalities for bioalcohols and phenolic bioproducts. Accordingly, in-situ removal modalities were designed for simultaneous acetone, butanol, and ethanol recovery. Additionally, a furfural removal modality from lignocellulosic hydrolysates was designed for upstream pretreatment. Solid-liquid adsorption was found to serve well each of the recovery modalities characterized here. More hydrophobic compounds such as butanol and furfural are readily recovered from aqueous solutions via adsorption. The primary operational drawback to adsorption is adsorbent recovery and subsequent desorption of the product. Novel magnetically separable mesoporous carbon powders (MMCPs) were characterized and found to be rapidly separable from solutions at 91% recovery by mass. Thermal desorption of value added products was found efficient for recovery of butanol and furfural. Fufural was desorbed from the MMCPs up to 57% by mass with repeated adsorption/thermal desorption cycles. Butanol was recovered from MMCPs up to an average 93% by mass via thermal desorption. As another valuable renewable fermentation product, phenol was also collected via in-situ adsorption onto Dowex Optipore L-493 resin. Phenol recovery from the resins was efficiently accomplished with tert-butyl methyl ether up to 77% after 3 washes.
ContributorsStaggs, Kyle William (Author) / Nielsen, David R (Thesis advisor) / Lin, Jerry S (Committee member) / Torres, César I (Committee member) / Lind, Mary Laura (Committee member) / Wang, Xuan (Committee member) / Arizona State University (Publisher)
Created2017
Description
One solution to mitigating global climate change is using cyanobacteria or single-celled algae (collectively microalgae) to replace petroleum-based fuels and products, thereby reducing the net release of carbon dioxide. This work develops and evaluates a mechanistic kinetic model for light-dependent microalgal growth. Light interacts with microalgae in a variety of positive and negative ways that are captured by the model: light intensity (LI) attenuates through a microalgal culture, light absorption provides the energy and electron flows that drive photosynthesis, microalgae pool absorbed light energy, microalgae acclimate to different LI conditions, too-high LI causes damage to the cells’ photosystems, and sharp increases in light cause severe photoinhibition that inhibits growth. The model accounts for all these phenomena by using a set of state variables that represent the pooled light energy, photoacclimation, PSII photo-damage, PSII repair inhibition and PSI photodamage. Sets of experiments were conducted with the cyanobacterium Synechocystis sp. PCC 6803 during step-changes in light intensity and flashing light. The model was able to represent and explain all phenomena observed in the experiments. This included the spike and depression in growth rate following an increasing light step, the temporary depression in growth rate following a decreasing light step, the shape of the steady-state growth-irradiance curve, and the “blending” of light and dark periods under rapid flashes of light. The LI model is a marked improvement over previous light-dependent growth models, and can be used to design and interpret future experiments and practical systems for generating renewable feedstock to replace petroleum.
ContributorsStraka, Levi (Author) / Rittmann, Bruce E. (Thesis advisor) / Fox, Peter (Committee member) / Torres, César I (Committee member) / Arizona State University (Publisher)
Created2017
Description
Electro-Selective Fermentation (ESF) combines Selective Fermentation (SF) and a Microbial Electrolysis Cell (MEC) to selectively degrade carbohydrate and protein in lipid-rich microalgae biomass, enhancing lipid wet-extraction. In addition, saturated long-chain fatty acids (LCFAs) are produced via β-oxidation. This dissertation builds understanding of the biochemical phenomena and microbial interactions occurring among fermenters, lipid biohydrogenaters, and anode respiring bacteria (ARB) in ESF. The work begins by proving that ESF is effective in enhancing lipid wet-extraction from Scenedesmus acutus biomass, while also achieving “biohydrogenation” to produce saturated LCFAs. Increasing anode respiration effectively scavenges short chain fatty acids (SCFAs) generated by fermentation, reducing electron loss. However, the effectiveness of ESF depends on biochemical characteristics of the feeding biomass (FB). Four different FB batches yield different lipid-extraction performances, based on the composition of FB’s cellular structure. Finally, starting an ESF reactor with a long solid retention time (SRT), but then switching it to a short SRT provides high lipid extractability and volumetric production with low lipid los. Lipid fermenters can be flushed out with short a SRT, but starting with a short SRT fails achieve good results because fermenters needed to degrading algal protective layers also are flushed out and fail to recover when a long SRT is imposed. These results point to a potentially useful technology to harvest lipid from microalgae, as well as insight about how this technology can be best managed.
ContributorsLiu, Yuanzhen (Author) / Rittmann, Bruce E. (Thesis advisor) / Torres, César I (Committee member) / Krajmalnik-Brown, Rosa (Committee member) / Arizona State University (Publisher)
Created2019