Developing A Better Method for Anaerobic Digestion Process Monitoring at a Large Wastewater Treatment Plant - Volatile Fatty Acids by Ion Chromatography with Inline Ultrafiltration

New Organic Monitoring Techniques
Oral Presentation

Prepared by X. Xu, A. Dyachenko
East Bay Municipal Utility District, 2020 Wake Ave, Oakland, CA, 94607, United States


Contact Information: xin.xu@ebmud.com; 510-287-1425


ABSTRACT

Short-chain volatile fatty acids (VFAs) with six or fewer carbons are important intermediates and metabolites in anaerobic digestion process and could be used as an indicator to monitor activity and state of the anaerobic microorganisms. East Bay Municipal Utility District (EBMUD; Oakland, CA) wastewater treatment plant serves approximately 740,000 customers and operates eleven 2 MG anaerobic digesters. To monitor digester stability, over 1,100 samples are analyzed annually for volatile acids (VA) using an energy- and labor-intensive distillation method (SM5560C). This study utilizes Ion Chromatography (IC) with inline 0.45 ┬Ám ultrafiltration system to analyze VFAs in anaerobic digester samples. Instrument setup, sample preparation and preservation, method parameters, accuracy, precision and sensitivity will be presented and compared to the traditional distillation/titration method. The distillation method only provides the total VA concentration and suffers poor accuracy, operational complexity, and safety concerns. IC with inline ultrafiltration technique provides speciation and accurate quantitation for up to eight VFAs measured in this study: formic, acetic, propionic, isobutyric, butyric, isovaleric, valeric and caproic acids. Temperature-controlled centrifugation of digester samples followed by inline ultrafiltration and IC analysis streamlines, automates, and shortens sample preparation. Compared to traditional distillation method, the detection and quantitation limits, and recoveries of individual VFAs using the IC method, have significantly improved for most of the volatile acids in this study. The new method not only addresses the drawbacks of the distillation method but also provides more data which are a better indicator of digester process and can be used by plant process engineers and operators to optimize anaerobic digesters operation. At least two months of VFAs monitoring data for several EBMUD thermophilic anaerobic digesters will be collected and correlations between VFAs results from IC system and distillation method, alkalinity, and other parameters will be presented.