Abstract
This study was conducted to investigate the speciation, bioavailability and environmental risk of heavy metals (HMs) in chicken manure (CM) and water-washed swine manure (WSM) and their biochars produced at different pyrolysis temperatures (200 to 800 °C). As the pyrolysis temperature increased, the remaining proportion, toxicity characteristic leaching procedure (TCLP), HCl and diethylenetriamine pentaacetic acid (DTPA) of HMs gradually declined. This result proved that the speciation of HMs in chicken manure biochars (CMB) and water-washed swine manure biochars (WSMB) was influenced by pyrolysis temperature. The proportions of stable fractions were enhanced with increased pyrolysis temperature and weakened the HM validity for vegetation at 800 °C. Finally, the results of the risk assessment showed that the environmental risk of HMs in CMB and WSMB decreased with increasing pyrolysis temperature. Therefore, pyrolysis at 800 °C can provide a practical approach to lessen the initial and underlying heavy metal toxicity of CMB and WSMB to the environment.
Highlights
This study was conducted to investigate the speciation, bioavailability and environmental risk of heavy metals (HMs) in chicken manure (CM) and water-washed swine manure (WSM) and their biochars produced at different pyrolysis temperatures (200 to 84.61% (200 °C) to 74.25% (800 °C))
Chen et al.researched the amounts of HMs, effective HMs (extracted by diethylenetriamine pentaacetic acid (DTPA)), radicals and decomposed biochar in corn stover and pig excrement and in converted biochar at 300 °C and 500 °C and found that the inorganic matter in biochar significantly immobilises the available heavy metals compared to the heavy metals in the feedstock[18]
The results indicated that the heavy metals in CM and WSM were at a moderate risk level
Summary
This study was conducted to investigate the speciation, bioavailability and environmental risk of heavy metals (HMs) in chicken manure (CM) and water-washed swine manure (WSM) and their biochars produced at different pyrolysis temperatures (200 to 800 °C). As the pyrolysis temperature increased, the remaining proportion, toxicity characteristic leaching procedure (TCLP), HCl and diethylenetriamine pentaacetic acid (DTPA) of HMs gradually declined. This result proved that the speciation of HMs in chicken manure biochars (CMB) and water-washed swine manure biochars (WSMB) was influenced by pyrolysis temperature. The main purpose of the present study is to (1) assess the bioavailability and ecological toxicity of HMs in chicken manure biochar (CMB) and water-washed swine manure biochar (WSMB) using a sequential extraction process (BCR), diethylenetriamine pentaacetic acid (DTPA), HCl leaching, and a toxicity characteristic leaching procedure (TCLP) and (2) assess potential ecological risks
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