Chemical forms and risk assessment of heavy metals in sludge-biochar produced by microwave-induced low temperature pyrolysis

Abstract

Biochar, a stable, carbon-rich solid produced during biomass pyrolysis, has been widely used in soil conditioning. A promising option to alleviate the problem of sludge management. In this study, Cr, Ni, Zn, Cd, As, Pb and Cu were studied owing to their relatively high content in the sludge and their potential to cause environmental damage. Sludge-biochars were produced at different temperatures

Migration and transformation of heavy metals during the microwave-assisted thermal hydrolysis of sewage sludge

“…Ni mainly existed in acid-soluble/exchangeable fraction in the raw sludge (Figure 3). The concentration of Ni in acid-soluble/exchangeable fraction decreased with the increasing temperature, which was similar to the results of sludge pyrolysis process ( Jin et al 2016;Liu et al 2016). The concentrations of Ni in mobile forms decreased by 11.86%, 32.07%, 44.74%, 41.33% and 38.79%, respectively, while the concentration of Ni in oxidizable fraction increased significantly after microwave treatment.…”

“…Heavy metals in the sewage sludge are present inside microbial cells, or adsorbed by EPS (Dewil et al 2006;Dewil et al 2007). Microwave treatment could destroy the structure of cells and EPS of the sludge (Wang et al 2015;Liu et al 2016), which may also lead to the release of metals from solid phase into liquid phase. Thus, the release of metals could result in the decrease of the total concentrations (mg/kg-TS) of metals in the solid phase, with the reduction of heavy metals present in unstable forms.…”

Profiles and drivers of antibiotic resistance genes distribution in one-stage and two-stage sludge anaerobic digestion based on microwave-H2O2 pretreatment

“…8%. Then, the sludge was stored at 4°C and screened through 18mesh sieve before use and MW-H 2 O 2 pretreatment to remove the sands and other small inorganic matters existed in the WAS (Liu et al, 2015b;Liu et al, 2016b). The TS concentration of WAS after sieving was ca.7.6%.…”

Environmental risk assessment in livestock manure derived biochars

“…The degree of contamination of biochar can be evaluated using the GAI, as described by Liu and co-workers. 30 This pollution index is generally used by researchers for environmental analysis, soil, 31 and road dust, 32 and can be defined by the following formula: where C n is the measured content of a particular heavy metal in PM, SM, PMB, or SMB, and B n is the background value for the heavy metal. The B n values of Cd, Cr, Zn, Cu, Pb, Ni, and Mn used in this study were 0.08, 64, 90, 25, 26, 30, and 380 mg kg −1 , respectively.…”

“…The degree of contamination of biochar can be evaluated using the GAI, as described by Liu and co-workers. 30 This pollution index is generally used by researchers for environmental analysis, soil, 31 and road dust, 32 and can be dened by the following formula:…”