Modeling and Experimental Study of an Open Channel Raceway System to Improve the Performance of Nannochloropsis salina Cultivation
Year: 2014
Type: article
Abstract: Lipid-rich microalgae are a potentially favorable alternative source of liquid fuels, and the use of open channel raceways has been proposed as a potential method for their mass cultivation.Studies on energy return on investment (EROI) show that open pond raceways are not feasible enough to be commercialized, but can be considered as a future commodity if energy can be recovered from both lipids and biomass residue.Analyses also show that the energy input in the form of CO 2 , nutrients, and mixing account for approximately 85% of the total energy consumption for algal biofuel production.Therefore, the conceptual framework of this study was mainly focused on the improvement of the open pond cultivation of the photosynthetic microalgae, Nannochloropsis salina, to increase the EROI of the process.The preexisting open pond cultivation process was hypothesized to be procedurally improved through modifications such as the conversion of algae biomass residue (ABR) via anaerobic digestion (AD) and the addition of phase-change material (PCM) to the open pond surface.A numerical approach was also employed by modeling the demonstration-scale cultivation systems using computational fluid dynamics (CFD) integrated with a kinetic model.The growth kinetics of N. salina was integrated into a 3-dimensional CFD model.Validation in a 120-m 3 open channel raceway showed a good fit for the change in iii biomass, CO 2 , and nitrogen concentrations.The model also showed the characteristics of dead zones that tail off the bends and increase in biomass concentration.The light attenuation, which is dependent on pond depth and cell concentration, was also observed to drastically increase in the system as the biomass concentration increased.Sensitivity analysis showed that the model was particularly sensitive to the several species-specific parameters.In an attempt to improve the low biomass productivity in the open channel raceways, supposedly caused by excessive water evaporation, susceptibility to contamination, and sensitivity to ambient influences, hexadecane was introduced as a phase change material (PCM) to cover the pond surface.The existing model was modified to accommodate an immiscible secondary phase that flowed in conjunction with the pond medium.Simulated results were compared with the 150-d data acquisition of light intensity, temperature, nutrient concentration, and algal biomass acquired from a demonstration scale raceway pond constructed for the growth of N. salina and were observed to be in good agreement with one another.Additional energy can be generated from ABR by means of anaerobic digestion (AD), but is inhibited by the byproducts of excessive protein degradation.Fat, oil, and grease waste (FOG) from a local municipal waste receiving facility was co-digested with ABR to evaluate the effects on methane yield and degradation of carbohydrates, lipids, and proteins.Co-digestion of ABR and FOG allowed for an increased loading rate while increasing methane yield.Lipids were the key contributor to methane yields.ix
Author: Stephen Y. Park
Institution: The Ohio State University
Language: English
Field: Energy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2616715772