Title: Turbulence and nutrient interactions that control benthic algal production in an engineered cultivation raceway Authors
Submitted to: Algal Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 2, 2013
Publication Date: January 20, 2013
Repository URL: http://handle.nal.usda.gov/10113/56578
Citation: Blersch, D., Kangas, P., Mulbry III, W.W. 2013. Turbulence and nutrient interactions that control benthic algal production in an engineered cultivation raceway. Algal Research. 2:107-112. Interpretive Summary: Algal Turf Scrubbing (ATS) is an engineered system for growing attached, lawn-like, filamentous algae on sloping surfaces over which wastewaters of many types can be pulsed. Algae grow using the nutrients in the wastewater and are removed from the system by weekly harvesting. Compared to conventional municipal wastewater treatment processes, ATS systems have relatively low capital and operational costs, but do require large land areas and people on-site to harvest the algae. In most instances, they also require lots of water pumping. Although flow turbulence provided by wave action stimulates algal growth in ATS, relatively little is known about the relationship of flow turbulence, water nutrient concentrations and algal growth. The objective of this study was to investigate the interaction between flow turbulence and nutrient concentration on the growth rate of attached algae in laboratory scale algal turf scrubbers. Results showed that, as expected, the algal growth rate increased with increased nutrient concentrations. At the highest nutrient concentrations tested, algal growth rate was strongly influenced by water flow turbulence. These results are important for determining the most cost efficient means to grow algae for nutrient removal or biomass production for bioenergy.
Technical Abstract: Flow turbulence can be a controlling factor to the growth of benthic algae, but few studies have quantified this relationship in engineered cultivation systems. Experiments were performed to understand the limiting role of turbulence to algal productivity in an algal turf scrubber for benthic algal cultivation. Volumetric flow rate and wave surge frequency were independently manipulated, operating over a range of nitrogen loading rates, and the effects on algal biomass productivity were measured through periodic sacrificial harvest. Productivity followed a saturation relationship versus nitrogen loading rate for the range of turbulence conditions. When flow rate was held constant, a maximum productivity of 27g dry weight per square meter per day was observed at a tipping frequency of 17 per min. at high nitrogen loading rates, with lower productivities at higher and lower frequencies. The productivity was similar (26g dry weight per square meter per day) when the volumetric flow rate was increased while surge frequency was held constant. Productivity was seen to be influenced by wave surge power, itself strongly determined by wave amplitude as set by volumetric flow rate. These results contribute to the understanding of the limiting factor effects of flow turbulence on algal production that can inform the optimization of the benthic algal cultivation.