Caracterização do resíduo de fundo de tanque de carcinicultura de águas oligohalinas

Abstract

Shrimp farming in oligohalin waters has standing out in the aquaculture sector for achieving higher productivity compared to saltwater cultivation. Related to this are the issues that forward the viability of the activity with regard to environmental responsibility, and involve effluent disposal and waste generation. Regarding the residues generated in the process some studies indicate that the sedimented residue at the bottom of the pond has the potential to be used as organic fertilizer. Therefore, the objective of this work was to characterize the bottom residue of oligohalin water shrimp farming pond with purpose to understand the geochemical conditions in the face of oxyreduction conditions that can contribute to the process of eutrophication and contamination of the environment. The physical-chemical parameters such as reactive phosphorus, total ammoniacal nitrogen (NAT), nitrite (NO2–) and nitrate (NO3–) of the effluent were quantified in the laboratory, while the potential of oxyreduction (Eh), pH, dissolved oxygen (OD), electrical conductivity (CE), temperature (T), total dissolved solids (STD) and salinity were obtained by reading in a Hanna HI 9828 multiparametric probe. As for the residue, granulometry was evaluated, pH, CE, calcium (Ca2+), magnesium (Mg2+), sodium (Na+), potassium (K+), carbon (C), nitrogen (N), organic matter (M.O), cation exchange capacity (CTC), assimilable P, base saturation (V%), percentage of exchangeable sodium (PST) and C/N ratio, showed low concentrations of OD and Eh, indicating moderately reduced environment. Nitrogen compounds (NAT, NO2– and NO3–) were within the standards established by CONAMA. Reactive phosphorus presented high concentrations in the effluent and may favor the process of eutrophication of the medium. The quantification of CTC, V%, Ca2+, Mg2+ and assimilated P were significant in the bottom residue of shrimp pond, indicating favorable characteristics for reuse in agricultural production. The textural relationship of the residue was classified as silt franc, indicating higher accumulation of nutrients at the bottom of the pond especially the assimilated P.