Plenary Lecture

Formation, Occurrence and Determination of Volatile Fatty Acids in Environmental and Related Samples

Professor Bogdan Zygmunt
Co-Author: Anna Banel
Department of Analytical Chemistry
Gdansk University of Technology
11/12 Narutowicza Str., 80-952
Gdansk, Poland
E-mail: zygmuntb@chem.pg.gda.pl

Abstract: Volatile fatty acids (VFA) are short chain alkane monocarboxylic acids containing from 2 to 8 carbon atoms in a molecule. They are formed in the process of anaerobic biodegradation of larger organic molecules and therefore are commonly present in municipal wastewater, effluents of food industry, cattle and swine farm wastewater, sewage sludge, landfill leachate, feces, urine, etc. VFAs play an important role in biological wastewater treatment, whereby their content ratio to phosphorous and nitrogen determine the effectiveness of removal of compounds of these elements by microorganisms. They are the most important intermediates in conversion of organic waste in landfills into methane. On the other hand, VFAs can have some harmful effects on the environment.
They should be monitored at different steps of wastewater treatment, in landfill leachate and also in treated wastewater and water bodies and some other samples. Different techniques have been used to determine the total content of VFAs in water and air. When individual VFA content is to be known, which is increasingly often the case, separation techniques, especially gas chromatography (GC), must be used. GC can separate both free acids and their derivatives. Increased selectivity and lower detection limit can be achieved by converting VFAs into derivatives containing fluorine atoms and then the application of GC with electron capture detection or by using mass spectrometry (MS) with negative chemical ionization for free acids.
Relatively clean aqueous samples can be directly injected into GC for analysis, possibly after removal of solid particles by centrifuging. In other cases, sample preparation is needed. It is generally based on matrix exchange and possible increase in analyte concentration to the value above the quantitation limit. Diethyl and methyl-t-butyl ethers (DDE, MTBE) were found to be appropriate solvents for VFAs extraction from water. Application of MTBE for extraction and GC-MS for the analysis proper permitted to determine VFAs in municipal, cattle and swine farm wastewater and in landfill leachates. Attempts were also made to apply headspace and solid phases microextraction and combination of both for VFAs isolation followed by GC-MS determination.