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- All Subjects: Algal biofuels
- Creators: Rittmann, Bruce E.
Description
Carbon dioxide (CO2) levels in the atmosphere have reached unprecedented levels due to increasing anthropogenic emissions and increasing energy demand. CO2 capture and utilization can aid in stabilizing atmospheric CO2 levels and producing carbon-neutral fuels. Utilizing hollow fiber membranes (HFMs) for microalgal cultivation accomplishes that via bubbleless gas-transfer, preventing CO2 loss to the atmosphere. Various lengths and geometries of HFMs were used to deliver CO2 to a sodium carbonate solution. A model was developed to calculate CO2 flux, mass-transfer coefficient (KL), and volumetric mass-transfer coefficient (KLa) based on carbonate equilibrium and the alkalinity of the solution. The model was also applied to a sparging system, whose performance was compared with that of the HFMs. Typically, HFMs are operated in closed-end mode or open-end mode. The former is characterized by a high transfer efficiency, while the latter provides the advantage of a high transfer rate. HFMs were evaluated for both modes of operation and a varying inlet CO2 concentration to determine the effect of inert gas and water vapor accumulation on transfer rates. For pure CO2, a closed-end module operated as efficiently as an open-end module. Closed-end modules perform significantly worse when CO2-enriched air was supplied. This was shown by the KLa values calculated using the model. Finally, a mass-balance model was constructed for the lumen of the membranes in order to provide insight into the gas-concentration profiles inside the fiber lumen. For dilute CO2 inlet streams, accumulation of inert gases -- nitrogen (N2), oxygen (O2), and water vapor (H2O) -- significantly affected module performance by reducing the average CO2 partial pressure in the membrane and diminishing the amount of interfacial mass-transfer area available for CO2 transfer.
ContributorsShesh, Tarun (Author) / Rittmann, Bruce E. (Thesis advisor) / Green, Matthew (Committee member) / Torres, Cesar (Committee member) / Arizona State University (Publisher)
Created2018
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