Potencial de adsorção de fosfato por solos naturais em reservatórios do semiárido: uma abordagem em microcosmos

Abstract

Eutrophication is one of the main causes of the deterioration of water quality and its management is of paramount importance. Reducing the external input of nutrients is essential, but it is often not enough due to the internal fertilization process of the sediment. In this context, eutrophication control measures applied to aquatic ecosystems are necessary to accelerate recovery. Among the restoration techniques currently used, there is the removal of soluble reactive phosphorus (FSR) through the use of solid phase adsorbents, natural or modified, one of the techniques used in Geoengineering. Applying the technique on a full scale can be costly, making it difficult to apply it in developing countries. Aiming to reduce the cost of application, the objective of this study was to evaluate the phosphate adsorption potential of two natural adsorbents from the semi-arid Potiguar region, Plano Haplic (PLA) and Luvissol Chromic (LUV), in natural water from reservoirs in the same region. The adsorption potential was evaluated through adsorption tests in natural water from the Dourado and Gargalheiras reservoirs, using a phosphate concentration gradient from 0 to 100 mg L-1. With soil application in natural water without the addition of phosphate, a treatment that approximates the actual application condition, the phosphate concentration increased, that is, there was release. LUV had maximum adsorption capacities of 14.9 and 23.9 mg L-1 for, respectively, Dourado and Gargalheiras, while PLA had a maximum adsorption capacity of 16 and 17 mg L-1. According to the isotherms found, the maximum adsorption capacity values can be overestimated, since the isotherms did not reach equilibrium. The maximum phosphate removal efficiency occurred close to the initial concentration of 50 mg L-1. Phosphate removal was found only at high FSR concentrations, compared to the natural conditions of the studied semiarid reservoirs. Thus, natural semi-arid soils did not obtain adequate adsorption potentials for use in the restoration of eutrophic ecosystems in the same region. Despite the high maximum adsorption capacities, the generated isotherms did not reach equilibrium, the values found for this parameter may have been overestimated.