Monitoring Volatile Fatty Acids and Carbonate Alkalinity in Anaerobic Digestion: Titration Methodologies

Volatile fatty acids and carbonate alkalinity have long been considered the key variables in most anaerobic digestion (AD) monitoring strategies as they not only reflect the current process status, but also mirror their response to incoming imbalances and provide an indication of the buffer capacity of digesters to process disturbance and imminent digester failure caused by sudden operational changes. Titration methods are generally acknowledged for routine monitoring and control of biogas plants due to their simplicity and cost-effectiveness. Systematical evaluation and comparison of these methods have not been carried out in sufficient depth to date. Basic theories of titration methods, their development, influencing factors, and evolution during recent years are reviewed. This review may provide assistance for selection of the most appropriate titration method and in the development of new methods for stability monitoring in the AD processes.