Applied Engineering in Agriculture Vol. 31(3): 365-375 2015 American Society of Agricultural and Biological Engineers ISSN 0883-8542 DOI 10.13031/aea.31.10209 365 ENERGY PRODUCTIVITY OF THE HIGH VELOCITY ALGAE RACEWAY INTEGRATED DESIGN (ARID-HV) S. Attalah, P. M. Waller, G. Khawam, R. D. Ryan, M. H. Huesemann ABSTRACT. The original Algae Raceway Integrated Design (ARID) raceway was an effective method to increase algae culture temperature in open raceways. However, the energy input was high and flow mixing was poor. Thus, the High Velocity Algae Raceway Integrated Design (ARID-HV) raceway was developed to reduce energy input requirements and improve flow mixing in a serpentine flow path. A prototype ARID-HV system was installed in Tucson, Arizona. Based on algae growth simulation and hydraulic analysis, an optimal ARID-HV raceway was designed, and the electrical energy input requirement (kWh ha -1 d -1 ) was calculated. An algae growth model was used to compare the productivity of ARID- HV and conventional raceways. The model uses a pond surface energy balance to calculate water temperature as a function of environmental parameters. Algae growth and biomass loss are calculated based on rate constants during day and night, respectively. A 10 year simulation of DOE strain 1412 (Chlorella sorokiniana) showed that the ARID-HV raceway had significantly higher production than a conventional raceway for all months of the year in Tucson, Arizona. It should be noted that this difference is species and climate specific and is not observed in other climates and with other algae species. The algae growth model results and electrical energy input evaluation were used to compare the energy productivity (algae production rate/energy input) of the ARID-HV and conventional raceways for Chlorella sorokiniana in Tucson, Arizona. The energy productivity of the ARID-HV raceway was significantly greater than the energy productivity of a conventional raceway for all months of the year. Keywords. ARID, ARID-HV, Algae, Chlorella, Energy, Pumps, Raceway, Simulation. n this research, we constructed a prototype ARID-HV (High Velocity Algae Raceway Integrated Design) and we compared the energy productivity (kg algae / kWh) of the ARID-HV and conventional raceways by simulating algae growth and quantifying energy inputs. Algae raceways have high light exposure and are less expensive than bioreactors. However, cold water temperature during cold seasons can dramatically decrease algae production rate. In order to increase water temperature during cold periods, the original ARID (Algae Raceway Integrated Design) raceway was invented (Ryan et al., 2010; Crowe et al., 2012; Waller et al., 2012). Temperature was regulated by varying the water surface area between day and night. Removing the water from the shallow basins at night reduced longwave radiation to the night sky, convective heat loss, and evaporation (latent heat of vaporization). Although effective at raising temperature, the electrical energy input was high and flow mixing was poor; thus, the ARID-HV was developed in this research in order to minimize electrical energy input and improve mixing by creating a turbulent high velocity flow regime in a serpentine flow path. Algae growth rate, μ (d -1 ), is a function of temperature, light, and other variables. Figure 1 shows the growth rate response surface versus temperature and light intensity for Chlorella sorokiniana (DOE 1412). The peak growth rate occurs at 36°C (Huesemann et al., 2013). Thus, daytime algae culture temperature should be as close to 36°C as possible in order to optimize growth rate of this species. On the other hand, cold temperature at night reduces dark respiration rate and biomass loss for Chlorella sorokiniana. Thus, there is an advantage to lowering the temperature at night. A surface energy balance model was used to simulate hourly raceway temperatures in the ARID-HV and conventional raceways in Tucson, Arizona over a 10-year period. The temperature output from the energy balance model was used as the input for the algae growth model. The overall objective of the present research was to design, construct, and evaluate the ARID-HV prototype raceway and to compare with the energy productivity of the conventional raceway. There were four specific objectives: Submitted for review in April 2013 as manuscript number MS 10209; approved for publication by the Machinery Systems Community of ASABE in January 2015. Presented at the 2012 ASABE Annual Meeting as Paper No. 121338040. Mention of company or trade names is for description only and does not imply endorsement by the USDA. The USDA is an equal opportunity provider and employer. The authors are Said Attalah, MS Student, Agricultural and Biosystems Engineering Department, University of Arizona, Tucson, Arizona; Peter Waller, ASABE Member, Associate Professor, Agricultural and Biosystems Engineering Department, University of Arizona, Tucson, Arizona; George Khawam, ASABE Member, MS Student, Agricultural and Biosystems Engineering Department, University of Arizona, Tucson, Arizona; Randy Ryan, Assistant Director, Arizona Agricultural Experiment Station, College of Agriculture, University of Arizona, Tucson, Arizona; and Michael Huesemann, Staff Research Engineer, Marine Sciences Laboratory, Coastal Biogeochemistry Group, Pacific Northwest National Laboratory, Sequim, Washington. Corresponding author: Said Attalah, University of Arizona, Agricultural and Biosystems Engineering Dept., 1177 E. 4 th St. Shantz 403, Tucson, AZ, 85721; phone: 520-223-5053; e-mail: sattalah@email.arizona.edu. I