Thermal dehydration of urban biosolids with green liquor dregs from pulp and paper mill. (1st May 2020)

• Record Type: Journal Article
• Authors: Gomes, Luciano A.; Santos, Andreia F.; Góis, José C.; Quina, Margarida J.
• Is Part Of: Journal of environmental management. Volume 261(2020)
• Publication Date: 2020-05-01
• Subjects: Drying -- Sewage sludge -- Dregs -- Soil application -- Phytotoxicity -- Kinetic modelling; Environmental policy -- Periodicals; Environmental management -- Periodicals; Environment -- Periodicals; Ecology -- Periodicals; 363.705
• DOI: 10.1016/j.jenvman.2019.109944
• Languages: English
• ISSNs: 0301-4797

Abstract

Abstract: This study aims to investigate the sewage sludge (SS) drying process by incorporating a by-product formed in the pulp and paper industry (green liquor dregs - GLD) as drying adjuvant. Through an innovative approach, the drying kinetics was modelled, and the final dried product was tested for soil applications. After the characterization phase, small cylinders of SS without and with 0.15 g GLD g SS −1 wb (SS_GLD) were dried in isothermal conditions at 70, 100, and 130 °C. The experimental data were fitted by Fick's second law and thin-layer models, and good results were achieved in both cases (R 2 > 0.98 and RMSE <0.05). Although only a slight improvement was observed, the best conditions for drying biosolids were found with the addition of GLD at 130 °C, where the drying rate was 30.88 gH2 O kg −1 SSwb min −1 . In this condition, a decrease of 8% in the energy required for moisture evaporation was observed. Regarding the phytotoxicity tests with Lepidium sativum L. (garden cress), 60% improvement in EC50 was noticed for the sample with GLD when compared to the raw SS. The dried product SS_GLD complied with the regulations for soil applications regarding the potentially toxic metals (Cr, Ni, Cu, Pb, Zn, and Cd), and promoted an increase in soil organic matter and pH. However, further and in-depth studies should be conducted to assess the potential of SS_GLD application in agricultural soil. Highlights: Fick's second law and thin-layer models described adequately the experimental data. The maximum drying rate was obtained for SS with GLD at 130 C. GLD contain a low concentration of potentially toxic metals but high alkalinity. SS with GLD mixture increased the biomass content and raise soil pH.