New insight into the role of FDOM in heavy metal leaching behavior from MSWI bottom ash during accelerated weathering using fluorescence EEM-PARAFAC.

ABSTRACT

Fluorescence excitation-emission matrix (EEM) spectroscopy is a powerful tool to characterize DOM that interacts with heavy metals in MSWI bottom ash (IBA). Here, two fresh IBA samples collected from large MSWI plants were subjected to 33 days of accelerated weathering. Carbon content and fluorescence characterization of DOM and leaching behavior of heavy metals (Cu, Ba, Cr, Ni, and oxyanions) were monitored during the weathering. The mineralogical and chemical properties of IBA during the weathering process were also characterized. EEM combined with parallel factor analysis showed that fluorescent DOM could be decomposed into humic-like (C1, C2) and tryptophan-like substances (C3), while the accelerated weathering process can be further divided into three phases. Fitted cubic polynomials described well the changes in the specific intensity of fluorescence components. Humification and freshness indexes and SUVA results suggested the leached DOM contained a higher proportion of condensed aromatic structures and/or conjugation of aliphatic chains post-weathering. The results also revealed that adsorption of humic-like substances onto neo-formed reactive surfaces occurred quickly in the early stage of accelerated weathering; thereafter, biodegradation of lower molecular mass-hydrophilic organic carbon fraction plays a vital role in further reduction of Cu and Cr leaching in subsequent weathering. Oxyanions (Mo and Sb) became more mobile after 3 days of accelerated weathering, but their leaching was effectively reduced after the weathering process. A novel method for an IBA weathering treatment combined with enhanced microbial degradation is proposed. These findings provide new and inspiration for improving accelerated weathering technology.