Volatile Fatty Acids Method Study Reveals a Need to Update Analytical Methods

Presentation Description: The Central Marin Sanitation Agency’s (CMSA) continued desire to leverage existing infrastructure as it expands its co-digestion and renewable power delivery program, relies on accurate monitoring of CMSA’s anaerobic digestion process. The CMSA Laboratory (CMSAL) has monitored the anerobic digestion through traditional wet chemistry analyses. One of the primary analytical monitoring methods used to determine anaerobic digester heath is Volatile Fatty Acid (VFA) analysis using Standard Methods 5560C.

VFA analysis is an important element of assessing the condition of the anaerobic digestion process. Optimization of CMSA’s anaerobic digesters requires understanding of the composition and quantity of VFAs during all stages of the digestion process. VFA speciation interpretation provides operations an understanding of the current state of the anaerobic digesters and provides operational strategy options to improve performance. Regular analysis of VFA concentrations and their changes provides early detection of a potential anaerobic digester process upset.

Traditional titration methods do not differentiate VFA species, which are required to delineate potential biological stress. To streamline the CMSAL VFA analysis and differentiate VFA species, CMSA purchased and began the implementation of a VFA method development using a Metrohm Ion Chromatography (IC) system. Upon method development of this new analysis, significant differences were noted between the traditional Standard Method 5560C and the new IC analytical method. This study provides a summary of the various method parameters studied, such as sample preservation, analyte recovery differences, and critical method criteria sample analysis comparison.

The results from this study demonstrate key analytical factors laboratories should consider when developing a VFA analysis for solid matrices. Critical criteria such as colloidal impacts, centrifuge speeds and times, sample hold times, sample pretreatment, colloidal separation additive alternatives and VFA interpretation will be discussed within this presentation. These ground-breaking analytical findings could facilitate a significant update to Standard Methods 5560 and provide a framework for future developed analytical VFA methods. This analytical update will provide the cogeneration community key analytical information required for optimization of digestion processes as dependency on cogeneration is increased in the future.