Occurrence and Determination of Volatile Fatty Acids in Wastewater of Different Origin

Volatile fatty acids (VFAs) are aliphatic monocarboxylic acids containing from 2 to 8 carbon atoms. They are formed in anaerobic biodegradation of larger molecules and play an important role in biological wastewater treatment. They should be monitored in raw waste water, at different stages of its treatment and in treated wastewater. Usually, the determination of VFAs in environmental aqueous samples is preceded by pre-treatment based on VFA selective isolation by means of distillation, solvent extraction, solid phase microextraction, or gas extraction. For individual VFAs determination in the extracts, separation techniques, most often gas chromatography, are employed. In this work, extraction of selected C2-C8 VFAs with methyl-tert-butyl ether (LLE) from aqueous samples was tested and the separation and identification of VFAs in the extracts, by gas chromatography coupled with mass spectrometry (GC-MS) was studied. Open tubular capillary columns coated with Rtx-624 (crossbond 6% cyanopropylphenyl - 94% dimethyl polysiloxane)and Stabilwax-DA (crossbond polyethylene glycol treated with nitroterephtalic acid) were used. The limits of quantitation of LLE-GC-MS procedure were on the level of 0.1 to 0.5 mg L(-1). Unfortunately, for very "dirty" real samples containing many interfering substances some analyte acids could have been quantitatively determined at higher concentrations. Real samples of municipal raw and treated wastewater were successfully analysed. Dominant in all the samples was acetic acid.