Clinoptilolite removal of ammonia from simulated and natural catfish pond waters

The catfish-rearing industry has been a major contributor to a critical water table drawdown in the Mississippi Delta region, which is due to the ambitious pumping necessary to provide approximately 1.5 × 108 liters (40 × 106 gallons) of water per year per 0.08 km2 (20-acre) catfish pond. Furthermore, the market demand for catfish continues to grow rapidly. At present, the only way to meet this demand is to build more ponds and pump more water. Fish production might be increased by increasing fish density in existing ponds. Unfortunately, increasing fish density would aggravate problems of oxygen deficiency and toxic ammonia buildup. This study analyzed the use of a natural zeolite mineral to remove ammonia in a circulating system. After comparing a variety of zeolite, clinoptilolite from Death Valley Junction, California was selected for the model study because of having an ideal combination of NH4+ exchange capacity (218 mcq/100 g) and wet mechanical strength (slake-durability index of 98%). Packed column studies using the Death Valley Junction clinoptilolite produced flow rates from 50 to 300 bed volumes per hour using 1 mg/l ammonia per liter influent. Average effluent concentrations, using 1 mg/l ammonia influent, were achieved at less than 0.03 mg/l ammonia. When testing this system in simulated natural waters competing cations, particularly calcium and magnesium, reduced the zeolite's capacity for ammonia exchange. Capacity for ammonia exchange was further reduced when the system was operated in natural pond waters. Consequently, more frequent regeneration was required. This reduction in exchange capacity can probably be attributed to the organic, especially algal content of the natural pond water. Furthermore, frequent backflushing was required due to the constant fouling of the system by algac and other organics.