Diferentes misturas de esgoto doméstico e efluente de cabine de pintura: avaliação da suplementação de carbono no cultivo de microalgas, potencial de biorremediação e acúmulo de carotenoides

Abstract

The paint booth effluent (PBE) generated during the painting and varnishing process of wooden furniture in the furniture industry has a high content of suspended solids and organic carbon in its composition, low levels of nutrients, such as nitrogen and phosphorus, in addition to the presence of chemical elements, such as aromatic solvents. Due to these characteristics, the efficient treatment of this effluent becomes difficult, often generating large expenses for companies. The present study, divided into three main lines of action, had as main objectives the evaluation of the biological treatment of PBE in high-rate algal ponds via the action of microalgae and the potential accumulation of carotenoids by the biomass. Firstly, the effect of different mixtures of PBE with domestic sewage (DS) on algal growth and on the production of total carotenoids from the biomass produced, under conditions of a culture medium poor in nutrients and with the presence of volatile organic compounds, was evaluated. It was observed that volumes of 25 and 50% of PBE in the culture medium generated the highest yields of chlorophyll-α (3.0 and 2.3 mg/L, respectively), and that values above 40% of PBE can inhibit the development of algae. After evaluating the algal growth and the potential production of value-added compounds, the present study evaluated the performance of different mixtures between PBE and DS in the treatment and production of biomass, seeking to determine the optimal mixture between the effluents, since the PBE can act as a supplemental source of carbon to DS. The mixtures were: D1 (0% PBE, 100% DS), D2 (18.75% PBE, 81.25% DS), D3 (37.5% PBE, 62.5% DS), D4 (56.25 % PBE, 43.75% DS) and D5 (75% PBE, 25% DS). Mixture D2 showed the best carbon, nitrogen and phosphorus ratio, resulting in the best primary and total productivity (0.08 g chl-α/m².day and 2.0 g volatile solids/m².day). It was found that the insertion of PBE in the medium positively affects the bioremediation performance, increasing the efficiencies of removal of compounds such as phosphorus (removal > 60%), nitrogen (100% removal) and organic matter (removal > 50%). In addition, the D2 mixture stood out for the greater recovery of nitrogen via assimilation by the biomass, reaching 19% more than the initial value. Finally, the third line of action aimed to investigate the effect of the nutritional control of the culture medium on the production and accumulation of carotenoids by the algae biomass. Compounds such as lutein and β-carotene were identified in the biomass (maximum 52.6 μg/g and 1.21 μg/g, respectively), and this accumulation was guided by the initial cultivation conditions. In short, it is concluded that it is possible to treat PBE via a high-rate algal pond, and that, in addition to the environmental benefit generated by the treatment, there is the possibility of generating value-added products, making the installation of treatment systems more attractive by PBE producing industries. It is recommended, in future studies, the performance of experiments on the improvement of cultivation conditions for the production of specific carotenoids and other value-added compounds.