Dissolved Organic Carbon Content and Leachability of Biomass Waste Biochar for Trace Metal (Cd, Cu and Pb) Speciation Modelling

Abstract

Dissolved organic carbon (DOC) interacts with dissolved trace metal affecting their mobility and bioavailability through the formation of DOC–metal complexes. Several types of biochar (BC) produced from slow pyrolysis of wood chips (WC), lignin (LG), and digested sewage sludge at 450 and 700 °C were tested for DOC leaching via batch and up-flow percolation test methods. Trace metal (Cd, Cu, and Pb) speciation modelling in BC eluates was carried out combining measured data (i.e., DOC, ph, temperature, and dissolved trace metal concentrations) with data reported in the literature regarding fractions of DOC that are inert or active (i.e., fulvic acids (FA) and humic acids (HA)) in metal binding. BC from LG (BCLG) and WC (BCWC) at 700 °C released lower cumulative amounts of DOC compared with BC at 450 °C in the range 0.02–0.07% and 0.06–0.09% of total carbon content, respectively. For both pyrolysis temperatures, BCWC exhibited a higher tendency to release DOC compared to BCLG. Speciation modelling results showed the predominance of FA and HA complexes of Cd, Cu, and Pb in all the eluates from BCWC and BCLG irrespective of the inert fractions of DOC or the different fractions of active FA and HA considered.

Biochar Derived from Domestic Sewage Sludge: Influence of Temperature Pyrolysis on Biochars’ Chemical Properties and Phytotoxicity

“…As for Cr, the concentrations significantly decrease in PSS1 (260°C) and PSS3 (610°C) and increase in PSS2 (420°C). ese results are different from the previous ones [61,91,92], which emphasize the increase of trace metals in the form of oxide and sulfide from 300 to 700°C. For instance, Méndez et al [92] found that biochar derived from sewage sludge pyrolyzed at 500°C retains 31% of Cu, 30% of Pb, and about 28% of Ni, Cd, and Zn compared to the raw feedstock.…”

“…As shown in Figure 1, the contents of trace metals in the sewage sludge vary significantly in the following order Zn > Cu > Cr > Pb > Cd, where Zn reaches 3 ppm whereas the content of Cd is only 0.027 ppm. e same trend was reported in the findings of Mancinelli et al [91], as Zn is the element with the highest concentrations followed by Cu, and Cd is the trace metal with the lowest concentrations in the feedstock and the biochars. Previously, Yuan et al [21] explained that Cd tends to volatilize during pyrolysis and the other trace metals initially present in the feedstock generally remain and become concentrated in the biochar.…”

“…As confirmed by recent studies, one of the main characteristics of the pyrolysis process is the sanitization of the sludge's pathogens and the destruction of organic compounds [14]. e presence of metals in the biochar is likely dependent on the origin of the feedstock or on pyrolysis conditions that may promote their accumulation in the biochar or their volatilization [44,90,91]. In this study, trace metals (Cu, Cd, Zn, Pb, and Cr), initially present in the raw SS, remain concentrated in the biochars (Figure 1).…”

Review: Dissolved Organic Carbon Content of Biochar Varying With the Type of Feedstock and the Pyrolysis Temperature

“…The high coefficient of variance (>100%) calculated for the means of all the three groups of feedstocks may be due to the wide range of pyrolysis temperatures considered, specifically, BC from cellulose rich feedstock (400-750 °C), BC from lignin-rich feedstock (350-800 °C), and for BC from manure and waste (350-900 °C). Data were retrieved from the following sources: Alburquerque et al 2014;Baltrėnaitė et al 2016;Gaskin et al 2008;Graber et al 2014;Hass et al 2012;Heitkötter, Marschner 2015;Jeong et al 2016;Jones et al 2011;Khan et al 2015;Liu et al 2015;Lu et al 2014;Mancinelli et al 2017;Mukherjee, Zimmerman 2013;Peng et al 2016;Rodríguez-Vila et al 2016;Sáez et al 2016;Smebye et al 2016;Smith et al 2016;Spokas et al 2014;Tang et al 2016;Yue et al 2016;Zeng et al 2015;Zhang et al 2015;Zheng et al 2012 Mean DOC content of BC from manure and waste (Fig. 2c) was the highest (2.24-5.35 g/kg) in the temperature range of 350-450 °C.…”

“…A relatively limited fraction of carbon has been reported to be released from BC as DOC (Liu et al 2016), representing between 0.10 and 2.65% of the total carbon (TC) in the BC at 300 °C (Liu et al 2015), between 0.04 and 0.24% of the TC in the BC at 450 °C (Mancinelli et al 2017;Jones et al 2011), between 0.1 and 0.4% of the TC in the BC at 650 °C (Mukherjee, Zimmerman 2013), and between 0.016 and 0.35% of the TC in the BC at 700 °C (Mancinelli et al 2017).…”