Structural and functional relationships of activated char briquettes from pyrolysis of sewage sludge for methylene blue removal

• Published in: Journal of cleaner production Vol. 259; p. 120907
• Main Authors: Deng, Wenyi, Hu, Menghao, Ma, Jingchen, Su, Yaxin, Ruan, Roger
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 20.06.2020
• Subjects: Activated char briquette; Adsorption; Methylene blue; Sewage sludge pyrolysis; Adsorption; Sewage sludge pyrolysis; Activated char briquette; Methylene blue
• DOI: 10.1016/j.jclepro.2020.120907
• ISSN: 0959-6526

Activated char briquettes from pyrolysis residue of sewage sludge were prepared and characterized for methylene blue removal. The briquettes were prepared with different binder (phenolic resin) content (15–25 wt%), compression pressure (2.5–7.5 MPa) and thickness (3.5–14 mm), followed by CO2 or H2O activation under different temperatures. The effects of these parameters on the compositions, surface properties, apparent densities, mechanical properties, methylene blue adsorption kinetics and isotherms were systematically investigated. The results indicated that all of the prepared briquettes showed a characteristic of hierarchical porous structures, as well as high mechanical performance with impact resistant index much higher than 50. The increase of binder content from 15 to 25 wt% can result in marked increase of surface area (SBET), total pore volume (VT), apparent density and mechanical performance of the briquettes. According to the adsorption kinetics of methylene blue, the highest equilibrium adsorption capacity (qe,exp) for CO2-activated and H2O-activated briquettes were 194.6 and 203.6 mg/g. Both the increase of binder content and activation temperature markedly enhanced qe,exp, due to the increase of SBET and VT. qe,exp was much lowered by increasing the compression pressure or the thickness of briquettes, owing to the increased diffusion resistance and blockage of diffusion pathways inside briquettes. The adsorption kinetics data of the briquettes fit well into a pseudo-first order model system, suggesting physical adsorption of methylene blue onto briquettes surface. The adsorption isotherms of methylene blue indicated that both the CO2-activated and the H2O-activated briquettes followed a Langmuir isotherm model. The leaching tests of briquettes revealed that the leaching concentrations of Cd, Cr, Cu, Pb, Ni and Zn were much lower than the Chinese standard limits. [Display omitted] •Briquettes showed high mechanical performance with the maximum IRI of 1811.1.•Blockage of diffusion pathways will be negligible with the briquette thickness ≤3.5 mm.•The adsorption rate of briquettes is 1-2 orders of magnitude lower than that of particulate adsorbents.•MB adsorption onto the briquettes was physical and monolayer adsorption process.•Leaching concentrations of heavy metals were much lower than the Chinese standard limits.