3 / 2021-04-28 11:53:54

The release behaviar of metals in biochar of co-pyrolytic sewage sludge and apple branch

Sludge; Apple branches; Co-pyrolysis; Metal fixation; Pb2+/Cr3+; Release.

Excessive sludge from sewage water treatment plant and lignocellulosic biomass are two main organic wastes, which can be recycled by pyrolysis technology, however, the transfer and transformation of harmful metals in sludge has not been fully investigated. In this study, a rapid co-pyrolysis method was proposed to treat sewage and pruning apple branches, and the release behavier of Pb and Cr in the obtained biochar was elucidated. The pyrolytic temperature and the mixing ratio of apple branch and activated sludge during co-pyrolysis, as well as the environmental conditions on the release of heavy metals Pb²⁺ and Cr³⁺ in biochar were detailedly investigated. the results show that high temperature pyrolysis was conducive to the fixation of metals and substantially reduced the release of metals. The release of Cr³⁺ under pyrolysis at 600 ℃ (1.266 μg L^-1) was only 1/10 of that at 400 ℃ (11.977 μg L^-1). The mixing ratio of apple branches and activated sludge of 1:1 was optimum to the fixation of Cr³⁺, and 1:2 was to the fixation of Pb²⁺ under the experimental conditions. In addition, the acidic environment is beneficial to the release of Pb²⁺, while the alkaline environment promotes the release of Cr³⁺. The discrepency of Cr³⁺ and Pb²⁺ release may be attributed to the transformation of metals and the interaction of biochar. This work can provide a method for heavy metal fixing while the organic wastes were recycled.