Validação de método para determinação de ácidos graxos voláteis em efluentes de biorreatores anaeróbios através de cromatografia gasosa

Abstract

Secondary biological anaerobic processes used for wastewater treatment have developed rapidly since the mid-20th century and are currently used in most Sewage Treatment Plants (ETEs) around the world. Sludge produced throughout the treatment is the main byproduct and is a semi-solid material containing organic matter, pathogenic microorganisms, toxic substances and even heavy metals withdrawn from the liquid phase. However, by applying appropriate treatment, it can transform itself from a problem residue into a product with economic value: modern and low-cost technologies can be reused in the material (nutrients and heavy metals) and its energy potential (biogas production - 70% methane). Volatile fatty acids (AGVs) are important intermediates of anaerobic digestion and their rate of production largely determines the rate of methane production. The knowledge of the concentration of VFAs in the sludge under treatment allows monitoring the performance of the reactor. The gas chromatography coupled to mass spectrometry (GC / MS), for the determination of VFAs, stands out from others for being efficient and selective, and allows structural information, molar mass, among other advantages. The validation of a method for its detection ensures the reliability of the results. In the present work, the Thermo Scientific gas chromatograph (TRACE 1300) was used and the detector was a Thermo Scientific mass spectrometer (ISQ QD - Single Quadrupole) with an SPB-624 intermediate polarity column. Recognized brand reagents And previous tests were done to define suitable conditions for the method (CG / MS). Validation was done following the recommendations of INMETRO and ANVISA. The results showed that the validation of the method (GC / MS) for determination of VFAs with the chosen column and the best chromatographic conditions obtained were adequate, taking into account the validation parameters: linearity (r ≥ 0,9843), precision Coefficients of variation <20%), sensitivity (angular coefficients ≥ 238218), limit of detection (0.030 mg.L-1 - 0.848 mg.L-1), limit of quantification (0.120 mg.L-1 - 2.827 mg.L -1), accuracy (100% - 110% - higher concentrations). Applied to real matrices, the method proved to be satisfactory because the retention times were very similar to the patterns used.