Monitoring foaming potential in anaerobic digesters

[Display omitted] •A simple method was developed to measure foaming potential in sludge from anaerobic digesters.•Total solids had a great effect on foam height as well as propensity.•The digester sludges can be classified into three groups by the simple method.•Both foam height and foam propensity can be used to classify the foam property.•The parameter of ΔHmax-after or ΔPmax-after represents foam stability. Foaming in anaerobic digestion (AD) systems for biogas generation can give serious operational problems. The cause of such foaming events is often unclear, and it is therefore not an easy task to predict and subsequently apply preventative measures. Methods for the measurement of the foaming potential of digester sludge are often implemented, but no standardized method is available. In this study, we investigated parameters influencing the foam formation during experimental aeration tests of full-scale digester sludge, including air flow, time, and total solids concentration, and proposed an optimized method for standard use. In a survey of 16 full-scale AD systems located at wastewater treatment plants in Denmark, all sludge samples were classified into three groups (non-foaming, pre-foaming, and actually foaming) according to their foam height/propensity and stability. Extensive surveillance of plants with the proposed classification system will enable the determination of cut-off values to help to identify foaming or pre-foaming sludge, and to associate these with operational conditions leading to foaming episodes.