Hydrolysis rates of domestic wastewater sludge using biochemical methane potential tests

Abstract

Domestic wastewater treatment can be improved by reducing energy consumption and increasing carbon recovery, which can be achieved using anaerobic digestion of sludge with methane recovery at ambient temperature. Hydrolysis can be a limiting step in anaerobic digestion, and characterisation of hydrolysis rates and process models should improve design and operation of treatment systems. The hydrolysis of primary sludge and secondary sludge were examined using biochemical methane potential (BMP) tests, with the monitoring of volatile solids concentrations and pH values at 25^oC and 37^oC, and data analysis using MATLAB non-linear least squares curve fitting to a first order hydrolysis model. Low reduction of solids was observed at 25^oC compared to 37^oC, and higher hydrolysis rates at 25^oC than at 37^oC. A correlation was observed between the first order model, digestion time and the reduction of solids based on coefficients of determination (R²). Model predictions were close to observed values, and therefore, the model should be reliable in predicting hydrolysis of sludge at 25^oC and 37^oC.

Keywords: hydrolysis; domestic wastewater; sludge; biochemical methane