Desenvolvimento de um sistema de recirculação com uso de wetlands construídas para efluentes da piscicultura / Development of a recirculating system using constructed wetlands for aquaculture effluents

AUTOR(ES)
FONTE

IBICT - Instituto Brasileiro de Informação em Ciência e Tecnologia

DATA DE PUBLICAÇÃO

22/06/2012

RESUMO

Global aquaculture has been growing very fast in recent decades due to several factors, including: population growth, demand for low calorie protein and especially the reduction of natural fish stocks. Brazil has enormous potential to become a world leader in fisheries production in captivity. However, the development of aquaculture in Brazil must be conducted on economically and environmentally basis. Thus, the rational use of water and monitoring the effluent parameters should be of paramount importance for such development to occur. The present study aimed to evaluate the efficiency of subsurface flow constructed wetlands, the feasibility of using low cost materials in the filters construction along with the plant Vetiver (C. zizanioides) in treatment of effluent from tilapia culture (O. niloticus) in pilot scale, with closed water cycle system (recirculation). To that end, a constructed wetland system composed by three types of support media was built, such as: gravel, expanded clay and a homogeneous mixture of both substrates (MIX). The performance of the beds was measured by assessments of physical and chemical water parameters and by the assessment of fish development. The assessment of substrate selection and the influence of Vetiver plant, the gravel had better performance for both water quality and fish development. It was also evident the importance of the plant to improve the bed performance. Percentual reduction of physico-chemical parameters was higher in treatments with the presence of the plant. For detention hydraulic times (TDHs) and flow assessment, treatments with maximum flow showed better performance. One might expect the opposite to occur, namely that reductions in water quality parameters were higher in the reduced flow, since it would imply higher TDHs (mean value of 0,53 hour for reduced flow compared to mean value of 0,29 hour for maximum flow) and consequently greater contact between non treated water and the biological microbial community. Considering fish development, treatments with reduced flow (mean value of 0,06 L s- 1) showed better results, with higher values for biometric indicators. And when evaluating the effect of fish density, animal development was greater at lower density treatments (13,04 kg/m3), which presented lower mortality rates, regardless of substrate type used in filters. The lower density of fishes per cubic meter resulted in better quality of treated water (greater reductions of important physico-chemical parameters), probably also due to better non-treated water quality. In summary, it can be concluded that the recirculation system proposed is feasible for commercial purposes, as the filter type MIX was effective in reducing critical parameters for good development of tilapia. The combination of gravel with expanded clay probably led to greater microbial community diversity, favoring the reduction of important physico-chemical parameters. Though the HDT should be relatively high in constructed wetlands, in the present study the rapid exchange of water is critical for the maintenance of high levels of water dissolved oxygen and to reduce nitrite concentration, ensuring good tilapia development.

ASSUNTO(S)

tilapia (peixe) aquicultura peixe - criação vetiver tilápia (fish) aquaculture fish vetiver

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