Effects of Coagulant Treatments on Aquaculture Effluent Quality

Abstract

Coagulant treatments for improving the water quality of effluents from channel catfish ponds were evaluated at the Auburn University Fisheries Research Unit (FRU), Auburn, Alabama. Gypsum, alum with agricultural limestone, ferric chloride, and ferric chloride with non-ionic polymer (polyacrylamide) were utilized at application rates typically used in wastewater treatment. Samples were collected from each treatment vessel after 0, 1, 2, 4, 6, 12, 24, 48, and 72 hours and analyzed for turbidity, total suspended solids, inorganic suspended solids, particulate organic matter, total phosphorus, soluble reactive phosphorus, total nitrogen, total ammonia nitrogen, and 5-day biochemical oxygen demand. Most measured variables were greatly reduced within 1 hour after the alum with agricultural lime treatment. Alum with agricultural limestone treatment enhanced removal of turbidity, suspended solids, and phosphorus during sedimentation of pond effluents. This treatment was greatly superior to treatments with gypsum, ferric chloride, and ferric chloride with non-ionic polymer, and was selected for evaluation in a settling pond. In the field study, the greatest benefit from alum with agricultural limestone was expressed during sedimentation for 1 or 6 hour periods in the settling pond. Reductions in concentrations of potential pollutants in other treatments were mainly attributed to settling. Alum with agricultural limestone treatment application may remove high concentrations of organic and inorganic pollutants from pond effluent. In situations where settling basins have insufficient hydraulic retention time (< 1-hour), alum and agricultural limestone application can enhance the effectiveness of settling. However, benefits were much less for a 24-hour sedimentation period. If space is available for a sedimentation basin with a 24-hour hydraulic retention time, alum with agricultural limestone treatment probably would not be necessary.

Key Words:

• Coagulants
• pond treatment
• alum
• channel catfish
• pond effluent
• Ictalurus punctatus