Determination of Volatile Fatty Acids Produced in Anaerobic Digestion Process of Wastewater by Gas Chromatography

A method for determination of volatile fatty acids( VFAs) produced in anaerobic digestion process of wastewater by capillary column gas chromatography( GC) was established. The optimal determination conditions were selected through the investigation of the p H for sample pretreatment and temperature-programming condition of the GC column. The repeatability and recovery of the samples were studied. The optimal determination conditions were as follows,samples were acidified approximately to p H = 3 by phosphoric acid; the initial GC column was 95 ℃,which was hold for 2 min; the temperature rose to 140 ℃ at a rate of 10 ℃ / min; and the temperature rose to 200 ℃ at a rate of 40 ℃ / min and kept for 3 min. Under the optimized conditions,the relative standard deviations of the four kinds of acids were4. 2% to 7. 2%( n = 7). The method detection levels( MDL) were 0. 2 mg / L to 0. 4 mg / L. The recovery rates of the actual wastewater samples were 92. 1% to 108%. The results indicated that the method has high degree of separation,good repeatability,short testing time and good linearity,and it can determine the contents of volatile fatty acids produced in anaerobic digestion process of wastewater quickly and accurately.