OPTIMIZATION OF ALGAL TURF SCRUBBERS FOR LARGE-SCALE SUPER-INTENSIVE AQUACULTURE

Algal turf scrubbers (ATS) are widely used for nitrogen and phosphorous removal from natural waterways. The system is typically arranged as a downward sloping flow-way onto which a mesh matrix is attached to assist in colonization by epiphytic algae.  As water flows over the developed algae mat, soluble nitrogen and phosphorus are assimilated by the algae and water quality is ameliorated.  This is of particular interest in the field of aquaculture as up to 50% of the protein in feeds is excreted as ammonia, which can be toxic to the organisms.  Removing ammonia comes at a cost to the producer and only increases as biomass density of production increases.  Unlike traditional nutrient removal methods, because ATS is solar-driven and does not need supplemental CO₂, once established it operates at low cost.  ATS systems have proven effective in treating agricultural runoff as well as effluent from bivalve aquaculture.  In order to effectively remove nutrients, a large amount of algal biomass must be produced which, among other variables, may be due to matrix material and shapes.  In addition, harvesting biomass is essential to stimulate further growth and increase nutrient removal.  

In this study, a twelve lane (1-foot wide, 40-foot length) ATS system was utilized to test the effectiveness of different matrices (n=3) control, 2-D, 3-D, and "advanced" 3-D, in yielding the highest amount of algal biomass (g AFDW/m²/day) and greatest ability to remove nutrients.  Once the most effective mesh material was determined, a subsequent experiment was conducted to determine the effect of different harvest schedules.  Four different harvest intervals (4, 7, 10, and 14 days) were chosen to examine their effectiveness in yielding the highest amount of biomass.  Water samples were taken daily to monitor nutrient removal.  Solar intensity, wind speed, and precipitation were also measured daily.  Twice a day (a.m. and p.m.), dissolved oxygen, salinity, temperature, and pH were measured with a portable meter and recorded for each ATS lane.  Biomass was harvested and analyzed for biochemical composition to determine its potential as an aquaculture feed ingredient or bioenergy source.  Based on this data, an optimal ATS size and design that would be appropriate for nutrient removal in common commercial super-intensive shrimp aquaculture may be modeled.