Effect of organic fertilization on nitrification, production of solids and water use in BFT system
The biofloc system is characterized by the use of bacteria to remove nitrogenous compounds from water: heterotrophic and chemoautotrophic bacteria. In this way, different techniques can be used for the formation and maintenance of bioflocs. The first experiment aimed to analyze biofloc formation techniques and their effects on the use of water, on the production of solids and on the zootechnical performance of Litopenaeus vannamei. Three treatments were tested: without supplemental organic fertilization, fertilization according to the nominal ammonia reading (chemoautotrophic) and fertilization according to the estimated ammonia production (heterotrophic). The water quality parameters were affected by the treatments. There were significant differences in zootechnical parameters,with better values found in the mixed treatment. The total volume of water used showed lower values in the mixed treatment, while the solids removed were almost four times higher in the heterotrophic treatment compared to the others. These results showed the importance of adopting a mixed chemoautotrophic heterotrophic biofloc system to optimize the use of water and decrease the production of solids. However, it is known that the carbon/nitrogen ratio can influence the establishment of the nitrification process and influence the production of solids. A second experiment was carried out to verify the effect of the C/N ratio on the composition of heterotrophic and nitrifying bacteria and on the zootechnical performance L. vannamei. Four treatments (n = 3) were tested using the following C/N ratios: 7.5/1, 10/1,12.5/1 and 1/15. Water parameters were monitored. Water samples were collected to detect the population growth of bacteria by the fluorescent in situ hybridization (FISH) technique. Only ammonia differed between treatments. Nitrification was affected in the highest ratio, although there were no differences in bacterial composition. The total volumes of water used and the solids removed (estimated) showed lower values in treatments 10/1 and 12.5/1. The results showed the importance of reducing the amount of carbon to decrease the total suspended solids in the BFT system.