Study on natural water loss characteristics and mathematical model of CaO conditioned sludge

The effects of CaO addition ratio, airflow rate and bulking thickness on the natural water loss characteristics of municipal sludge treated by CaO were studied. The results showed that sludge water loss rate was proportional to airflow rate and CaO addition ratio, but inversely proportional to bulking thickness. The experimental data were well fitted by the general model based on the Page model with the root mean square error of 6.34%, which could better simulate the natural dewatering process of CaO-treated sludge. The effective water diffusion coefficient of the sludge calculated using the Page model was 9.96×10⁻⁹-1.65×10⁻⁷. The natural water loss time was positively correlated with the CaO addition ratio and airflow rate, and negatively correlated with the bulking thickness. Using the total cost per unit water loss as the evaluation index, the Fmincon function in MATLAB software was applied to calculate the optimal drying parameters under the condition of the lowest total cost per unit water loss. The optimal combination of drying parameters was: CAO addition ratio 0.02, airflow rate 0.6 m/s, sludge accumulation thickness 7 mm.