Turbulence and nutrient interactions that control benthic algal production in an engineered cultivation raceway

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 (ATS) for benthic algal cultivation. Volumetric flow rate and wave surge frequency were independently manipulated in an ATS 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 26.8 g dW m(-2) d(-1) was observed at a wave surge frequency of 17 min(-1) at high nitrogen loading rates, with lower productivities at higher and lower frequencies. The productivity was similar (26.4 g dW m(-2) d(-1)) when the volumetric flow rate was increased with surge frequency held constant. Productivity was 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. (C) 2013 Elsevier B.V. All rights reserved.