NaHCO3-enhanced sewage sludge thin-layer drying: Drying characteristics and kinetics. Issue 10 (27th July 2017)

• Record Type: Journal Article
• Authors: Zhou, Jiazhen; Zhang, Ruina; Wang, Xing; Chen, Shanping; Luo, Anran; Niu, Dongjie; Chai, Xiaoli; Zhao, Youcai
• Is Part Of: Drying technology. Volume 35:Issue 10(2017)
• Page Start: 1276
• Page End: 1287
• Publication Date: 2017-07-27
• Subjects: Modified Midilli -- moisture diffusion -- NaHCO3 -- sludge -- thin-layer drying; Drying -- Periodicals; Desiccation; 660.28426
• DOI: 10.1080/07373937.2016.1249878
• Languages: English
• ISSNs: 0737-3937

Abstract

ABSTRACT: Drying sewage sludge is a highly energy-extensive process. For this reason, this work seeks to identify a reagent that can enhance the effectiveness of the drying process. In this study, drying experiments of sewage sludge were conducted at drying temperatures ranging from 100 to 160°C. NaHCO3 was selected as the drying reagent, which was added to the sludge before drying. The thin-layer drying characteristics of the sludge and sludge/NaHCO3 mixtures were later investigated and compared. Various mathematical models were used to simulate the sludge drying curves. It was found that adding 2 and 6% (wet basis) of NaHCO3 to the sludge was effective in improving the moisture diffusion during the drying process, whereas the drying rate of the sludge/NaHCO3 mixtures decreased when the addition of NaHCO3 was further increased to 10% (wet basis). When the addition ratio was 2%, the increase in the maximum drying rate was the largest. With coefficients of determination ( R 2 ) over 0.9999, the modified Midilli model proposed in this study was observed to be the most suitable model to describe thin-layer drying of sludge relative to the other models examined in terms of R 2, reduced χ 2, root mean square error, and residual sum of squares. The values of the diffusion coefficients at each temperature were obtained using Fick's second law of diffusion, which varied from 3.700 × 10 −9 to 1.085 × 10 −8 m 2 /s over the temperature range (i.e., 100–160°C). The activation energy of moisture diffusion was determined to be 27.57 kJ/mol. Scanning electron microscope images of the dried sludge and sludge/NaHCO3 mixtures indicated that the porosity of the sludge after drying increased with an increase in the NaHCO3 addition ratio. Overall, the results suggested that NaHCO3 is a suitable reagent to improve the drying efficiency of the sludge.