The thin-layer drying characteristics of sewage sludge by the appropriate foaming pretreatment

Abstract

As dewatered sludge is highly viscous and sticky, the combination of foaming pretreatment and drying process seems to be an alternative method to improve the drying performance of dewatered sludge. In this study, CaO addition followed by mechanical whipping was employed for foaming the dewatered sludge. It was found that the foams were stable and the diameters of bubbles mainly ranged from 0.1 to 0.3 mm. The drying experiments were carried out in a drying oven in the convective mode. The results indicated that foamed sludge at 0.70 g/cm(3) had the best drying performance at each level of temperature, which could save 35-45% drying time to reach 20% moisture content compared with the non-foamed sludge. The drying rate of foamed sludge at 0.70 g/cm(3) was improved with the increasing of drying temperature. The impact of sample thickness on drying rate was not obvious when the sample thickness increased from 2 to 8 mm. Different mathematical models were used for the simulation of foamed sludge drying curves. The Wang and Singh model represented the drying characteristics better than other models with coefficient of determination values over 0.99.

Draining solar drying of sewage sludge: Experimental study and modeling

“…The results show that the Midilli‐Kucuk model was the most reliable for describing the evolution of the reduced moisture content as a function of time in winter and summer seasons with R 2 equal to 0.99886 and 0.99998 and χ2 equal to 1.48 10 −4 and 6.41 10 −6 , respectively. This result agrees with the experimental drying results of sludge using an indirect solar dryer, 13 of mint, 43 apple, 46 thyme treated with distilled water, 47 and laurel noble. 48 However, for different drying conditions, the Wang and Singh model was the least suitable.…”

“…The curve proposed by Krischer and Kast 42 (−dX/dt) as a function of X is divided into three phases: product warm‐up phase (Phase 0), constant drying‐rate phase (Phase 1), and falling drying rate phase (Phase 2). By applying other methods of drying, the curves of the variation of drying rate as a function of the moisture content have the same appearance of the Krischer curve 13,31,43 …”

“…Bennamoun and Leonard 12 have estimated the experimental results of a cross‐flow belt dryer by empirical models. Wang et al 13 have used mathematical equations to simulate the sludge drying curves with a drying oven. To determine the most appropriate model to describe the drying curves of sludge with an indirect forced convection solar dryer, Idlimam et al 14 have adjusted the experimental drying curves by nine mathematical equations.…”

Drying behavior and thermo-gravimetrical kinetic analysis of foam-pretreated sewage sludge

“…An efficient modeling of drying curves could be used to perform an accurate estimate of the moisture content (%) of the foamed sludge at any time during the whole drying process. 29,30 In this research, the results of moisture content (%) versus drying time were tted to adequate empirical and semi-theoretical models, which are widely used to describe the kinetics in the drying process. Finally, non-linear regression techniques (Nonlinear Curve Fit (Dose Resp)) were successfully applied to simulate the whole drying process of S 2:2 at the ideal density of 0.6 mg L À1 , using the Origin Pro 8.0 soware based on the Levenberg-Marquardt method (nonlinear least square method).…”

Performance of rice straw fiber improving the drying of waste activated sludge

“…Thermal drying is the most widely utilized sludge drying technology nowadays. In order to obtain higher treatment efficiency with lower cost, in addition to systematic optimization and mechanism study of the established drying process, it is equally important to improve the exogenous conditions in order to achieve greater breakthrough [2]. The two significant exogenous factors in the sludge drying system are heat source and the physicochemical properties of sludge.…”