Characterization of intensive shrimp pond effluent and preliminary studies on biofiltration

Effluent from aquaculture ponds may add to receiving waters high levels of biochemical oxygen demand (BOD), inorganic and organic particulate matter, live algae, dissolved organic matter, ammonia, nitrite, nitrate, phosphate, and other potential contaminants. We evaluated a method that used the eastern oyster Crassostrea virginica and a macroalga, Gracilaria tikvahiae, for biofiltering the effluent from a pond used for intensive culture of Pacific white shrimp Litopenaeus vannamei.(2) Effluent flow rates of 2.0, 1.1, and 0.2% of pond volume/d were tested. Shrimp yield from the 0.5-ha pond after 129 d was 10,312 kg/ha; shrimp survival rate was 96.5%. Oyster biofiltration accounted for most of the decrease of turbidity, chlorophyll a, total suspended solids (TSS), and settleable solids. Following macroalgal biofiltration, decreases in ammonia, total nitrogen, and total phosphorus concentrations were observed. At a daily exchange rate of 7.5%, diversion of 1.1% of the pond volume to the treatment system removed 10-14% of the nitrogen, BOD, TSS, and phosphorus from the treated water. Successful implementation of this type of biofiltration system requires allocation of resources to manage the bivalves and the macroalgae under culture. Nevertheless, use of a similar system, along with best management practices, offers opportunities for improvement of effluent water quality.