Co-pyrolysis of sewage sludge/cotton stalks with K2CO3 for biochar production: Improved biochar porosity and reduced heavy metal leaching. (November 2021)

• Record Type: Journal Article
• Authors: Wang, Zhipu; Tian, Qingmei; Guo, Jing; Wu, Ruiqi; Zhu, Henan; Zhang, Hongzhen
• Is Part Of: Waste management. Volume 135(2021)
• Page Start: 199
• Page End: 207
• Publication Date: 2021-11
• Subjects: Sewage sludge -- Cotton stalks -- Co-pyrolysis -- Biochar -- K2CO3 activation; Hazardous wastes -- Periodicals; Refuse and refuse disposal -- Periodicals; 363.728
• DOI: 10.1016/j.wasman.2021.08.042
• Languages: English
• ISSNs: 0956-053X

Abstract

Graphical abstract: Highlights: Co-pyrolysis with a carbon source (straw) improves porosity. K2 CO3 activation increases biochar aromaticity. K2 CO3 activation improves both biochar porosity and specific surface area. K2 CO3 activation enhances the metal immobilization of biochar. Abstract: The co-pyrolysis of sewage sludge and biomass is considered a promising technique for reducing the volume of sewage sludge, adding value, and decreasing the risk associated with this waste. In this study, sewage sludge and cotton stalks were pyrolyzed together with different amounts of K2 CO3 to evaluate the potential of chemical activation using K2 CO3 for improving the porosity of the biochar formed and immobilizing the heavy metals present in it. It was found that K2 CO3 activation effectively improved the pore structure and increased the aromaticity of the biochar. Moreover, K2 CO3 activation transformed the heavy metals (Cu, Zn, Pb, Ni, Cr, and Cd) into more stable forms (oxidizable and residual fractions). The activation effect became more pronounced with increasing amount of added K2 CO3, eventually resulting in a significant reduction in the mobility and bioavailability of the heavy metals in the biochar. Further analysis revealed that, during the co-pyrolysis process, K2 CO3 activation resulted in a reductive atmosphere, increased the alkalinity of the biochar, and led to the formation CaO, CaCO3, and aluminosilicates, which aided the immobilization of the heavy metals. K2 CO3 activation also effectively reduced the leachability, and thus, the environmental risks of the heavy metals. Thus, K2 CO3 activation can improve the porosity of the biochar derived from sewage sludge/cotton stalks and aid the immobilization of the heavy metals in it.