Characterization of intensive shrimp pond effluent and preliminary studieson 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 east ern oyster Crassostrea virginica and a macroalga, Gracilaria tikvahiae, for biofiltering the effluent from a pond used for intensive culture of Pacifi c white shrimp Litopenaeus vannamei.(2) Effluent flow rates of 2.0, 1.1, an d 0.2% of pond volume/d were tested. Shrimp yield from the 0.5-ha pond afte r 129 d was 10,312 kg/ha; shrimp survival rate was 96.5%. Oyster biofiltrat ion accounted for most of the decrease of turbidity, chlorophyll a, total s uspended solids (TSS), and settleable solids. Following macroalgal biofiltr ation, decreases in ammonia, total nitrogen, and total phosphorus concentra tions 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, BO D, TSS, and phosphorus from the treated water. Successful implementation of this type of biofiltration system requires allocation of resources to mana ge the bivalves and the macroalgae under culture. Nevertheless, use of a si milar system, along with best management practices, offers opportunities fo r improvement of effluent water quality.