Estudo do processo semicontínuo de tratamento do soro do leite por microalgas em sistema aberto

Abstract

Due to environmental issues and the need for water recycling in the most diverse human activities, biological treatment can offer an adequate destination of the contaminants present in agro-industrial or industrial effluents in the form of biomass, promoting the carbon cycle in nature and which can even be used for obtaining chemicals and energy. Within this context, microalgae have been studied for the removal of nitrogen and phosphorus from effluents, but also chemical oxygen demand (COD) through mixotrophy, a mixture of autotrophic and heterotrophic metabolisms. In this context, and due to the scarcity of studies in this area, this work aims at the efficiency of microalgae for agro-industrial effluents in Alagoas, specifically whey. First, whey was characterized in relation to its chemical demand of oxygen (COD), nitrogen and total phosphorus. Tetradesmus obliquus LCE-01 was used, with whey concentrations of 1% (v/v) and light intensity of 100 μmol/(m2 s). The experiments were carried out in a semi-continuous manner, testing volumetric replacement rates of 20, 40, 60 and 80% at 3-day intervals of volumetric replacement. The experiments were monitored for chemical oxygen demand, total phosphorus, total nitrogen. The characterization of whey showed high levels of COD (around 53 g O2/L), as well as the essential nutrients for microalgal metabolism, nitrogen and phosphorus (around 1500 and 700 mg/L, respectively). In this study, the microalgae removed significant amounts of COD and total nitrogen varying between 50- 80 and 48-75%, respectively, and depending on the replacement rate. The phosphorus removal rate was increasing up to 40% volumetric replacement rate. It could be seen that high pH variations occurred at the highest volumetric replacement rates and that they significantly altered the microalgal concentration, showing a reduction in the phosphorus removal capacity, despite the fact that COD and total nitrogen removal were more efficient at these high removal rates. Studies with different organic loads could help to consolidate the results found in this study.