Tratamento de efluente de biodiesel pela integração dos processos de coagulação-floculação e foto-Fenton solar

Abstract

Biodiesel effluent demands treatment to enhance their organoleptic properties and to reduce the levels of organic load and toxicity. The pre-treatment of coagulation-flocculation, using 0.50 mmol L-1 Fe (NO3)3 as coagulating agent, was applied to the natural pH of the effluent (2.31) under magnetic stirring (350 RPM) and aeration (70 mL min-1) for a time of 48 minutes, followed by more 5 minutes to promote the flocculation of the particles. The use of this experimental condition allowed the removal of 87% of turbidity and 74% of apparent color. In the classical photo-Fenton solar process, it observed a low efficiency of removal of the chemical oxygen demand (COD), due to the formation of stable and soluble organic complexes with ferrous ions that inhibited the production of hydroxyl radicals. On the other hand, this limitation was overcome in the modified photo-Fenton solar process, using the protocol of multiple additions of the potassium oxalate binder at intervals of 50 kJ m-2 accumulated UVA radiation, during the photodegradation reaction. This process was also applied in order to reduce COD, biochemical oxygen demand after five days (BOD5) and toxicity, which were not obtained by the physical-chemical process of coagulation-flocculation. The best results were achieved using 1.0 mmol L-1 of ferrioxalate, allowing reducing in 72% COD and 76% BOD5 the treated effluent, after an accumulated UVA dose of 602 kJ m-2. Concomitantly, the acute toxicity to Vibrio fischeri was reduced from 70% to 6%. In view of this, this modality of can be a good alternative for decontamination and detoxification of this kind of wastewater, mainly considering that no further step of neutralization is need once that during the treatment the pH increase up to close 7, and that solar energy can be employed, reducing costs related to energy consumption compared to other treatments.