Reduction of waste generation in shrimp production under Biofloc Technology

The present master thesis addressed the need to improve the environmental sustainability of intensive Penaeus vannamei production in Europe by addressing one of the major limitations of the BFT system, the accumulation of nutrients, in particular nitrate and phosphate. The improve of the management of aerobic denitrification strategies could contribute to the development of more stable, water-efficient and environmentally sustainable shrimp farming systems adapted to European conditions. The effects of an aerobic denitrification system were evaluated on the reduction of nitrate and control of the water quality in a biofloc system, moreover the zootechnical parameters of the reared species Peneus vannamei were also analysed and confronted with the literature regarding other experiment with aerobic denitrification reactors and also anaerobic reactors. For this experiment three external bioreactors were used for a denitrification period of 48 h, for 4 times. The water samples were analysed to evaluate the evolution of the water quality parameters (ammonium, nitrite, nitrate, phosphate and alkalinity), and quantitative PCR were done to evaluate the different microbial community and their evolution during the denitrification period, different specific genes were selected to evaluate the presence of a determined enzyme. An organic carbon source, saccharose, was selected from different previous trials and used to accelerate and improve the microbial community grow. Inside the aerobic denitrification reactors nitrate removal efficiency was not complete but reached a percentage of 77,2%. Overall, thanks to the aeration system the aerobic bacteria were able to control and regulate the ammonium and nitrite levels under safe threshold and improving the water quality. Phosphate didn’t present any different between the control and the treatment group. Thanks to the molecular studies it was possible to determine the increase in abundance of bacteria simultaneously with the increase of Total Suspended Solids. The water quality parameters of the rearing tanks were very similar between the two treatments group through the experiment, only the nitrate presented a difference in the control group where it accumulated meanwhile in the denitrification group decreased till the end of the experiment. Regarding the zootechnical parameters they presented very similar results, only the final body weight exhibited a little difference in the denitrification group where it was slightly higher. Overall, the results of the present study show the high capacity of the denitrification system to remove the nitrate and while maintaining an optimal water quality, without impacting the health and growth of P. vannamei. In perspectives, longer periods should be tested to check long-term effects of the process.