Chemical phosphorus removal from aquaculture pond water and effluent

A series of trials were conducted in earthen ponds in Auburn, Alabama to determine the effectiveness of several chemical amendments in the removal of phosphorus from channel catfish (Ictalurus punctatus) pond water. Gypsum (calcium sulfate) applied to catfish pond water to maintain total hardness above 200 mg/L resulted in lower mean concentrations (P < 0.05) of total phosphorus (TP), chemical oxygen demand (COD), and phytoplankton biomass (as measured by concentrations of chlorophyll a). Gypsum applied to maintain hardness in pond water above 100 mg/L resulted in fewer water quality improvements, although mean COD concentrations and phytoplankton abundance (organisms/mL) were lower (P < 0.05) than in the control. Repeated applications of alum (aluminum sulfate) at 15 mg/L or hydrated lime (calcium hydroxide) at 30 mg/L resulted in little long-term improvement in pond water quality.; Drying and tilling of pond bottoms before ponds were filled and stocked reduced (P < 0.05) mean concentrations of TP, COD and chlorophyll a in pond water by 47%, 65% and 31%, respectively, compared to the control. Addition of phosphorus inactivating chemical amendments alum (at 1,120 kg/ha) or calcium carbonate (at 4,480 kg/ha) to dried and tilled catfish pond bottoms did not improve water quality (P > 0.05).; Application of alum at 50 mg/L to water remaining in catfish ponds immediately after seining for harvest did not result in greater (P > 0.05) removal of nutrients and solids than did settling alone. Within four hours of seining in both alum treated and untreated ponds, there was removal of more than 85% of TSS, 72% of turbidity, and more than 40% of biochemical oxygen demand (BOD).