Recuperação de reservatórios eutrofizados por atividades antrópicas : estudos em microcosmos
Abstract
The economic development of a country depends on good quality of water
available, so the conservation and restoration of water bodies are strategic
conditions for this to happen. However, water resources have become scarce
over the past decades, in quantitative and qualitative terms. A variety of human
activities have caused serious problems to the aquatic environment, and
eutrophication is one of the most responsible for the degradation of the quality
of water bodies, mainly caused by the artificial enrichment of nutrients,
especially phosphorus and nitrogen. There are currently two contrasting
scenarios: the excessive presence of phosphorus in aquatic ecosystems and, the
depletion of phosphate rock deposits, which endangers the water security and
the global food security. In this context the development of technologies aimed
at the recovery of the quality of aquatic ecosystems and phosphorus contained in
these compartments is of fundamental importance, since the global stock of
phosphate rocks is a finite resource and may be close to being exhausted.
Various technologies for the remediation of eutrophic environments have been
studied, however none of which aims to reuse of phosphorus in agriculture.
Thus, the aim of this study was to evaluate the sawdust as biosorbent material to
phosphorus aiming the recovery of the quality of water resources and its later
use as fertilizer in agriculture. The experiments were conducted in two stages,
first were assembled microcosm with water and sediment samples from
eutrophic reservoir Ibirité/MG, the total incubation time was 159 days, in this
time various parameters (physicochemical and chemical) were monitored in the
water column, interstitial water and sediment. After the end of this first
experiment arose any question about the phosphorus adsorption in sawdust, what motivated the development of a new experiment with samples of the Barra
Bonita/SP. This experiment was performed with sterile and non-sterile samples
as well as that had or not a previous addition of iron in the sawdust, the
incubation time was 240 and 247 days, respectively for non-sterile and sterile
experiment. The results of the first experiment (Ibirité) showed that there was a
reduction of 90.5% of orthophosphate in the water column of the microcosms
and sawdust adsorbed 16.2 μg g-1, this adsorption occurred mostly after 113
days of incubation. In the second experiment results showed that prior to
addition of iron not conducive to increased adsorption in the non-sterile
experiments, and the main adsorption mechanism may be not via the action of
bacteria oxidizing Fe (II). The higher adsorption in the second experiment took
place in sterile microcosm, where sawdust adsorbed 66.9 μg g-1 in the period of
247 days. Knowing that the success in the recovery of water bodies depends on
the reduction of external phosphorus sources, the studied technology has a good
potential application as a remediation technique and phosphorus reuse as
fertilizer, mainly because it is an inexpensive technique and easy to use.