Biodrying of pulp and paper secondary sludge: Kinetics of volatile solids biodegradation

• Kinetics of volatile solids biodegradation in batch biodrying was studied.
• The effect of air flow-rate (AFR) on the process was evaluated.
• Five kinetic models were analyzed with two statistical indicators.
• Higher AFR produces higher moisture content reduction and lower VS reduction.
• Satisfactory fitting of kinetic model to the experimental data of VS was achieved.

This study focuses on the kinetics of volatile solids (VS) biodegradation of the biodrying process using pulp and paper secondary sludge. The experiments were carried out with air-flow rates of 0.51, 1.61, 3.25 and 5.26 L/min kgVS) and initial moisture content of 64–66% w.b. Using five kinetic models and a nonlinear regression method, kinetic parameters were estimated and the models were analyzed with two statistical indicators. Higher air-flow rates cause greater moisture content reduction, lower temperature in the matrix, and lower VS reduction. At an air-flow rate as high as 5.26 L/min kgVS there is no biodrying but only convective drying. The kinetic models used successfully simulate the VS biodegradation under biodrying conditions, with a root mean square error (RMSE) between 0.007929 and 0.02744. In conclusion, we show for the first time that VS biodegradation in the biodrying process can be successfully modeled with a kinetic model.