Effect of the C: N ratio on Daphnia magna (Straus, 1820) production using tilapia farming wastewater / Efeito da relação C: N na produção de Daphnia magna (Straus, 1820) utilizando efluente do cultivo de tilapia

The purpose of this study was to produce Daphnia magna in wastewater from Tilapia farmed in a biofloc system, to evaluate three different carbohydrate:nitrogen ratios. The experiment was conducted for 30 days following a completely randomized experimental design, with the three treatments: C:N 10:1, C:N 15:1 and C:N 20:1, all fed with Chlorella vulgaris. The physical-chemical variables of the water analyzed were: temperature, dissolved oxygen (DO), pH, TAN, NO2, hardness and alkalinity. The following growth variables of the Daphnia were also evaluated: Maximum average density (MAD), Maximum density day (MDD), Specific growth rate (SGR), Doubling time (DT) and yield (Y). The water quality variables remained in the range of ideal conditions for the species, presenting significant differences (p <0.05) among the treatments for: pH, DO, hardness and alkalinity. Regarding the growth variables, significant differences (p <0.05) were observed, with higher MAD, Y and SGR values for the 10:1 treatment (3,433 ± 267 ind L-1, 245 ± 19 ind L-1 day- 1 and 45.3 ± 0.6% day-1, respectively) and lower for the 20:1 (1,011 ± 283 ind L-1, 55 ± 15 ind L-1 day-1 and 28.3 ± 1.6% day-1, respectively). The MDD occurred on day 12 for the 10:1 treatment and on day 18 for the 15:1 and 20:1 treatments. Alkalinity and hardness had stronger influence on the growth variables, which was also indicated by the simple linear regression. The principal component analysis (PCA), with 80% of explanation, identified high values of SGR, density and Y for the 10:1 and high values of alkalinity, hardness, DT and NO2 for the 20:1. Thus, the use of effluent from Tilapia farming in a biofloc system with a C:N ratio of 10:1 provided better production results for D. magna, demonstrating that it is an option for the production of live feed for aquaculture.

O presente trabalho teve como objetivo produzir Daphnia magna em água residual do cultivo de Tilápia em sistema de bioflocos, avaliando relações carboidrato:nitrogênio. O experimento teve duração de 30 dias seguindo delineamento experimental inteiramente casualizado, sendo os tratamentos: C:N 10:1, C:N 15:1 e C:N 20:1, todos com oferta de Chlorella vulgaris na dieta. Foram analisadas as variáveis físico-químicas: temperatura, OD, pH, TAN, NO2, dureza e alcalinidade; e as variáveis de crescimento: Densidade média máxima (DMX), Dia de máxima densidade (DMD), Taxa de crescimento específico (TCE), Tempo de duplicação (TD) e Rendimento (R). As variáveis de qualidade de água mantiveram-se na faixa ideal para a espécie, apresentando diferenças significativas (p<0,05) entre os tratamentos para: pH, OD, dureza e alcalinidade. Com relação às variáveis de crescimento, foram observadas diferenças significativas (p<0,05), com maiores valores de DMX, R e TCE para o tratamento 10:1 (3.433 ± 267 ind L-1, 245 ± 19 ind L-1 dia-1 e 45,3 ± 0,6 % dia-1, respectivamente) e menor para o 20:1 (1.011 ± 283 ind L-1, 55 ± 15 ind L-1 dia-1 e 28,3 ± 1,6 % dia-1, respectivamente). O DMD ocorreu no 12º dia para o 10:1 e no 18° dia para os 15:1 e 20:1. As variáveis alcalinidade e dureza tiveram destaque sobre as variáveis de crescimento sendo também evidenciada na regressão linear simples. Já a análise de componentes principais (PCA), com 80% de explicação, identificou altos valores de TCE, densidade e R para o 10:1 e, elevados valores de alcalinidade, dureza, TD e NO2 para o 20:1. Assim, o uso de efluente proveniente do cultivo de Tilápia em sistema de bioflocos com relação C:N de 10:1 propiciou melhores resultados produtivos para a D. magnademonstrando ser uma opção para a produção de alimento vivo para a aquicultura.

Effect of the C: N ratio on Daphnia magna (Straus, 1820) production using tilapia farming wastewater / Efeito da relação C: N na produção de Daphnia magna (Straus, 1820) utilizando efluente do cultivo de tilapia

The purpose of this study was to produce Daphnia magna in wastewater from Tilapia farmed in a biofloc system, to evaluate three different carbohydrate:nitrogen ratios. The experiment was conducted for 30 days following a completely randomized experimental design, with the three treatments: C:N 10:1, C:N 15:1 and C:N 20:1, all fed with Chlorella vulgaris. The physical-chemical variables of the water analyzed were: temperature, dissolved oxygen (DO), pH, TAN, NO2, hardness and alkalinity. The following growth variables of the Daphnia were also evaluated: Maximum average density (MAD), Maximum density day (MDD), Specific growth rate (SGR), Doubling time (DT) and yield (Y). The water quality variables remained in the range of ideal conditions for the species, presenting significant differences (p <0.05) among the treatments for: pH, DO, hardness and alkalinity. Regarding the growth variables, significant differences (p <0.05) were observed, with higher MAD, Y and SGR values for the 10:1 treatment (3,433 ± 267 ind L-1, 245 ± 19 ind L-1 day- 1 and 45.3 ± 0.6% day-1, respectively) and lower for the 20:1 (1,011 ± 283 ind L-1, 55 ± 15 ind L-1 day-1 and 28.3 ± 1.6% day-1, respectively). The MDD occurred on day 12 for the 10:1 treatment and on day 18 for the 15:1 and 20:1 treatments. Alkalinity and hardness had stronger influence on the growth variables, which was also indicated by the simple linear regression. The principal component analysis (PCA), with 80% of explanation, identified high values of SGR, density and Y for the 10:1 and high values of alkalinity, hardness, DT and NO2 for the 20:1. Thus, the use of effluent from Tilapia farming in a biofloc system with a C:N ratio of 10:1 provided better production results for D. magna, demonstrating that it is an option for the production of live feed for aquaculture.(AU)

O presente trabalho teve como objetivo produzir Daphnia magna em água residual do cultivo de Tilápia em sistema de bioflocos, avaliando relações carboidrato:nitrogênio. O experimento teve duração de 30 dias seguindo delineamento experimental inteiramente casualizado, sendo os tratamentos: C:N 10:1, C:N 15:1 e C:N 20:1, todos com oferta de Chlorella vulgaris na dieta. Foram analisadas as variáveis físico-químicas: temperatura, OD, pH, TAN, NO2, dureza e alcalinidade; e as variáveis de crescimento: Densidade média máxima (DMX), Dia de máxima densidade (DMD), Taxa de crescimento específico (TCE), Tempo de duplicação (TD) e Rendimento (R). As variáveis de qualidade de água mantiveram-se na faixa ideal para a espécie, apresentando diferenças significativas (p<0,05) entre os tratamentos para: pH, OD, dureza e alcalinidade. Com relação às variáveis de crescimento, foram observadas diferenças significativas (p<0,05), com maiores valores de DMX, R e TCE para o tratamento 10:1 (3.433 ± 267 ind L-1, 245 ± 19 ind L-1 dia-1 e 45,3 ± 0,6 % dia-1, respectivamente) e menor para o 20:1 (1.011 ± 283 ind L-1, 55 ± 15 ind L-1 dia-1 e 28,3 ± 1,6 % dia-1, respectivamente). O DMD ocorreu no 12º dia para o 10:1 e no 18° dia para os 15:1 e 20:1. As variáveis alcalinidade e dureza tiveram destaque sobre as variáveis de crescimento sendo também evidenciada na regressão linear simples. Já a análise de componentes principais (PCA), com 80% de explicação, identificou altos valores de TCE, densidade e R para o 10:1 e, elevados valores de alcalinidade, dureza, TD e NO2 para o 20:1. Assim, o uso de efluente proveniente do cultivo de Tilápia em sistema de bioflocos com relação C:N de 10:1 propiciou melhores resultados produtivos para a D. magnademonstrando ser uma opção para a produção de alimento vivo para a aquicultura.(AU)

Efficacy of fungal decolorization of a mixture of dyes belonging to different classes

Dyes are the most difficult constituents to remove by conventional biological wastewater treatment. Colored wastewater is mainly eliminated by physical and chemical procedures, which are very expensive and have drawbacks. Therefore, the advantage of using biological processes, such as the biotransformation of dyes, is that they may lead to complete mineralization or formation of less toxic products. To prove the possibility of using fungal processes for decolorization and other applications, the analysis of the toxicity of the processes' products is required. The decolorization of the mixture of two dyes from different classes - triphenylmethane brilliant green and azo Evans blue (GB - total concentration 0.08 g/L, proportion 1:1 w/w) - by Pleurotus ostreatus (BWPH and MB), Gloeophyllum odoratum (DCa), RWP17 (Polyporus picipes) and Fusarium oxysporum (G1) was studied. Zootoxicity (Daphnia magna) and phytotoxicity (Lemna minor) changes were estimated at the end of the experiment. The mixture of dyes was significantly removed by all the strains that were tested with 96 h of experimental time. However, differences among strains from the same species (P. ostreatus) were noted. Shaking improved the efficacy and rate of the dye removal. In static samples, the removal of the mixture reached more than 51.9% and in shaken samples, more than 79.2%. Tests using the dead biomass of the fungi only adsorbed up to 37% of the dye mixture (strain BWPH), which suggests that the process with the living biomass involves the biotransformation of the dyes. The best results were reached for the MB strain, which removed 90% of the tested mixture under shaking conditions. Regardless of the efficacy of the dye removal, toxicity decreased from class V to class III in tests with D. magna. Tests with L. minor control samples were classified as class IV, and samples with certain strains were non-toxic. The highest phytotoxicity decrease was noted in shaken samples where the elimination of dye mixture was the best.(AU)