Density profile modeling for real-time estimation of liquid level in anaerobic digester using multiple pressure meters

The liquid level of a bioreactor is an important operating parameter governing the hydraulic retention time. In this study, a novel method is proposed to estimate the liquid level of anaerobic digesters. The proposed method has an advantage over typical differential pressure measurement as it considers the heterogeneity of the digestate along the level using multiple pressure meters. The real-time measurement generates a model to fit the densities at different liquid columns, predicts the density of the surface layer and determines the overall liquid level. A pilot-scale (0.33 m3 working volume; 1.2 m liquid level) digester, equipped with seven pressure meters, was operated to test the methodology. The performance of the digester was confirmed stable during a long-term (175 d) operation. A set of density-pressure models was developed and were validated using the long-term experimental data. The new method employing cubic model showed significantly better estimation of the reactor level (mean error rate of 1.31%) with improved CDF, as compared with the traditional differential pressure method (mean error rate of 5.71%). The methodology proposed in this study is simple, robust, and cost-effective and can be used to provide additional insights into the operation of an anaerobic digester such as assessing the mixing efficiency. [Display omitted] •A novel method was developed to estimate the liquid level of digesters real-time.•The heterogeneity of digestate along the level was considered in model generation.•The densities of the liquid columns are simultaneously estimated with the level.•The method was validated and compared with traditional method in pilot scale.•Applying multiple manometers improved the accuracy of liquid level estimation in AD.