3RD INTERNATIONAL CONGRESS ON TECHNOLOGY - ENGINEERING & SCIENCE - Kuala Lumpur - Malaysia (2017-02-09)

Development Of Single Stage Nitrification-denitrification System For Aquaculture Effluent Treatment
For the treatment of aquaculture effluent, ammonia is the most considerable pollutant because of its toxicity for aquaculture. The most of aquaculture farm and aquarium applied dilution method and conventional nitrification-denitrification process for the effluent treatment. However, dilution method requires large amount of water such as 10 – 20% of aquarium volume. Conventional nitrification-denitrification process requires high operating costs such as aeration, dosing of alkaline agent for nitrification and carbon source for denitrification. On the other hand, down-flow hanging sponge (DHS) reactor, which is one of trickling filter type reactor equipped sponge as media, has high performance of nitrification with less amount of aeration by its high gas-liquid efficiency and high retention capacity of microbe. Furthermore, the sponge of DHS has both aerobic and anoxic zones at the surface of the sponge and inside the sponge, respectively. Therefore, DHS reactor has applicability for single-stage nitrification-denitrification process. In addition, both ammonia and nitrate can be utilized by plant as nutrients. In this study, the laboratory-scale experiment for aquaculture effluent treatment was conducted by using combined system of DHS reactor and hydroponic cultivation. The system consists of an aquarium with a volume of 120 L (water volume of 80 L), a hydroponic cultivation bed with a volume of 9 L and a DHS reactor with a volume of 1.4 L. Sodium acetate solution was added to the aquarium as a carbon source for denitrification. In addition, dipotassium hydrogenphosphate solution was added as source of potassium and phosphate, which are essential nutrients for plants, to balance the optimum ratio of nitrogen, phosphate and potassium. As a model of aquaculture and hydroponic plant, Cyprinus carpio and Cupsicum frutescens were selected respectively. At the beginning of the experiment, concentration of ammonia and nitrite kept below 0.5 mgN/L and 0.3 mgN/L, respectively. On the other hand, nitrate concentration increased to 40 mgN/L and pH was dropped to 5.6. On this occasion, ammonia concentration increased to 1.9 mgN/L. After addition of sodium acetate solution to the aquarium, pH recovered to 7.4 and ammonia concentration decreased to 0.6 mgN/L. Furthermore, proportion of accumulated nitrate to total inlet nitrogen decreased from 49% to 31%. These results indicate that addition of carbon source to the aquarium has a beneficial effect on not only denitrification, but also nitrification by increasing of the pH. In addition, approximately 25% of total inlet nitrogen was utilized by C. frutescens. Therefore, the proposed system had advantages over the dilution method and the conventional nitrification-denitrification process for treatment of aquaculture effluent.
Daisuke TANIKAWA, Yuka NAKAMURA, Takuya Fujihira, Takashi YAMAGUCHI