| 摘要 |
[Objectives] This study investigated the transformation of heavy metals during anaerobic digestion of excess sludge with alkali residue addition. [Methods] Two types of solid waste, i.e., excess sludge from a wastewater treatment plant and alkali residue from the ammonia-soda process, were selected as research objects. The effects of adding alkali residue calcined at 800 °C (AR800) on the speciation distribution and potential mobility of Zn, Cu, Cr, and As during anaerobic digestion were investigated. [Results] The speciation of heavy metals in the raw sludge varied significantly, and the stability ranked as Cr > As > Cu > Zn. After the addition of AR800, the stable fractions of all heavy metals in the digested sludge increased. The proportions of stable fractions of various metal reached their peak values on day 7 of anaerobic digestion. The differences in heavy metal fraction distribution were small under different dosages (2%, 5%, 8%). Considering both stabilization performance and economic cost comprehensively, 2% was selected as the optimal dosage. After digestion, the ratios of unstable-to-stable fractions for Zn, Cu, Cr and As decreased from 2.17, 0.35, 0.08 and 0.16 to 0.69, 0.04, 0.02 and 0.05, respectively. It indicates that alkali residue addition can effectively reduce the potential mobility of heavy metals. Mechanistically, alkaline substances increase the surface charge of digested sludge and promote the transformation of heavy metals into more stable fractions. [Conclusions] This study provides a theoretical basis for the safe land application of digested sludge under the “treating waste with waste” mode. |
