Abstract:
This study investigated the ammonia removal rate of nitrifying bacteria isolated from aquaculture ponds. Bacteria was collected from 4 sites i.e. (1) the shrimp culture pond at the Center of Excellence for Marine Biotechnology, Chulalongkorn University, (2) the marine aquarium filtration tank, Bangsaen Institute of Marine Science, Burapha University, (3) the outdoor shrimp pond in Chachoengsao Province, and (4) the outdoor spotted snail culture pond in Phetchaburi Province. The isolation was performed by immerging plastic biofilter media (R-190) in the pond for 45 days. The results showed that biofilter with bacterial seeding from the shrimp pond at Chulalongkorn University had the highest ammonia removal rate which was 47.20±1.86 mgNH₄-N/m²/d. This removal rate was significantly higher than those of other sources (P <0.05). In the second part, the effect of ammonia concentration on the ammonia removal rate of the acclimated nitrification biofilter was examined. The experiment was performed at different concentrations of ammonia i.e. 0, 0.5, 2 and 10 mg NH₄-N/L for 3-6 months. The results showed that the ammonia removal rate was in the range between 30-120 mgNH₄-N/L. Statistical analysis showed that there was an interaction between time and ammonia concentration during the biofilter acclimation period.
In the third part, the study investigated the efficiency of biofilter for ammonia removal in the simulated outdoor shrimp pond. The simulated shrimp pond consisted of two control and one treatment ponds. The first control had no biofilter and the other had un-acclimated biofilter. The treatment pond was supplied with active biofilter (pre-acclimated using nitrifying bacteria seeding from shrimp pond at Chulalongkorn University). All tanks were filled with 450 L of 30 PSU seawater with the alkalinity of 150 mg/L. White shrimp (Penaeus vannamei) was cultivated at the density 47 shrimp/m² without water exchange throughout the 90-day trial. The results showed that biofilter could maintain good water quality in treatment pond in which ammonia and nitrite concentrations were 0.25±0.45 mgNH₄-N/L and 0.80±1.32 mgNO₂-N/L, respectively. The active biofilter from the treatment pond had the maximum ammonia removal rate of 142.40±3.28 mgNH₄-N/L. Shrimp growth in the treatment pond was higher than that of control ponds. The last experiment investigated ammonia oxidizing bacterial (AOB) communities on biofilter. The results according to PCR-DGGE of 16S rDNA showed that AOB composition on the biofilter isolated from each sites was similar. Acclimation of nitrifying bacteria under laboratory condition resulted in the change of AOB composition on the biofilter. When pre-acclimated biofilter was applied to shrimp pond, AOB composition was then change to the natural AOB composition found in the water of shrimp pond.