Is Biochar from the Torrefaction of Sewage Sludge Hazardous Waste?

Thumbnail Image
Białowiec, Andrzej
Pulka, Jakub
Styczyńska, Marzena
Koziel, Jacek
Kalka, Joanna
Jureczko, Marcelina
Felis, Ewa
Manczarski, Piotr
Major Professor
Committee Member
Journal Title
Journal ISSN
Volume Title
Koziel, Jacek
Professor Emeritus
Research Projects
Organizational Units
Journal Issue
Is Version Of
Food Science and Human NutritionCivil, Construction and Environmental EngineeringAgricultural and Biosystems EngineeringEnvironmental ScienceToxicology

Improved technologies are needed for sustainable management of sewage sludge (SS). The torrefaction (also known as biomass “roasting”) is considered a pretreatment of SS before use in agriculture. However, it is not known whether the torrefaction has the potential to decrease heavy metals’ (HMs) leachability and the SS toxicity. Thus, the aim of the study was to evaluate the influences of the SS torrefaction parameters (temperature and process time) on HM contents in biochar, HM leachability, and biochar toxicity, and compare them with raw SS. The experiments were designed in 18 combinations (six temperatures, 200, 220, 240, 260, 280, and 300 °C; and three process times—20, 40, 60 min). Standard tests were used to determine HMs content, leachability, and toxicity. Results indicated that the torrefaction did not increase (p < 0.05) the HM content in comparison to the raw SS. The leachability of Zn, Ni, Cu, Cr, and Mn from SS biochars was similar to raw SS. However, the degree of leachability varied significantly (p < 0.05) from as low as 0.1% for Cu to high as 16.7% for Cd. The leachability of Cd (<16.7%) and Pb (<11.9%) from biochars was higher than from raw SS (<6.1% and <2.4%, respectively). The leachability of Cd from SS biochar, in five torrefaction combinations, was higher than the threshold value for hazardous waste. It is recommended that site-specific decisions are made for torrefaction of SS with respect to its HM content, as the resulting biochar could be considered as hazardous waste, depending on the feedstock. Moreover, the biochar produced under the whole range of temperatures during 20 min retention time significantly (p < 0.05) increased the Daphnia magna Straus mobility inhibition by up to 100% in comparison to the biochar obtained during 40 and 60 min torrefaction. Taking into account the increased leachability of specific HMs and D. magna Straus mobility inhibition, biochar should be considered a potentially hazardous material. Future research should focus on biochar dosage as a fertilizer in relation to its toxicity. Additional research is warranted to focus on the optimization of SS torrefaction process parameters affecting the toxicity.


This article is published as Białowiec, Andrzej; Pulka, Jakub; Styczyńska, Marzena; Koziel, Jacek A.; Kalka, Joanna; Jureczko, Marcelina; Felis, Ewa; Manczarski, Piotr. "Is Biochar from the Torrefaction of Sewage Sludge Hazardous Waste?" Materials 13, no. 16 (2020): 3544. DOI: 10.3390/ma13163544. Posted with permission.

Wed Jan 01 00:00:00 UTC 2020