Abstract
Combining hydroponics and aquaculture into aquaponic systems requires reconciling water quality parameters for the survival and growth of plants, fish, and nitrifying bacteria. The plants and fish are grown as cash crops while bacteria are expected to oxidize ammonia (fish by-product) into nitrite and finally nitrate which may be used by plants. The objectives of this project were to determine nitrification activity response to pH between 5.5 and 8.5 in recirculating trickling biofilters containing perlite medium. Total ammonia nitrogen concentration decreased from 5 to 0 mg L [sup-] in 12 (pH 8.5), 20 (pH 7.5), and 20-24 (pH 6.5) days after introduction of nitrifying bacteria to the perlite biofilters. Nitrite became measurable in the biofilter water at 8 (pH 8.5), 16 (pH 7.5), and 20-24 (pH 6.5) days after introduction of nitrifying bacteria. No nitrification occurred in the biofilters maintained at a pH of 5.5. These results indicate that ammonia conversion to nitrate in a perlite medium trickling biofilter startup cycle was significantly faster at pH 8.5 than at pH 7.5 and 6.5. The recommended pH for aquaculture systems is from 6.5 to 8.5 and for hydroponic systems is from 5.5 to 6.5. Results indicate the optimum pH for nitrification in this system is 8.5, however, the reconciling pH for aquaponics would likely be between 6.5 and 7.0 to optimize the production of the fish and plant cash crops.
