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

Organic amendment application affects the release behaviour, bioavailability, and speciation of heavy metals in zinc smelting slag: Insight into dissolved organic matter

Organic amendments are commonly used in assisted phytostabilization of mine wastes by improving their physicochemical and biological properties. These amendments are susceptible to leaching and degradation, resulting in the generation of dissolved organic matter (DOM), which significantly influences the geochemical behaviour of heavy metals (HMs). However, the geochemical behaviour of HMs in metal smelting slag driven by organic amendment-derived DOM remains unclear. In this study, we investigated the impact of cow manure-derived DOM on the release behaviour, bioavailability, and speciation of HMs (Cu, Pb, Zn, and Cd) in zinc smelting slag using a multidisciplinary approach. The results showed that DOM enhanced the weathering of the slag, with a minimal impact on the slag's mineral phases, except for causing gypsum dissolution. The DOM addition resulted in a slight increase in HM release from the slag during the initial inoculation period, followed by a reduction in HM release during the later period. Furthermore, the DOM addition increased the diversity and relative abundance of the bacterial community. This, in turn, led to a decrease in the dissolved organic carbon (DOC) content and enhanced the transformation of labile DOM compounds into recalcitrant compounds. The variation in HM release during various inoculation periods can be attributed to the bacterial decomposition and transformation of DOM, which further enhanced the transformation of HM fractions. Specifically, during the later period, DOM promoted the conversion of a portion of the reducible and oxidizable fractions of Cu, Pb, and Zn into the acid-soluble and residual fractions. Moreover, it partially transformed the reducible, oxidizable, and residual fractions of Cd into the acid-soluble fraction. Overall, this study provides new insights into the geochemical behaviour of HMs in slag governed by the coupling effect of DOM and the bacterial community. These findings have implications for the use of organic amendments in assisted phytostabilization of metal smelting slag. ENVIRONMENTAL IMPLICATION: Metal smelting slag is hazardous due to its high levels of HMs, and its improper disposal has serious consequences for the ecosystem. Organic amendments are employed in assisted phytostabilization of the slag site by improving its microecological properties. However, the impact of organic amendment-derived DOM on HM migration and transformation in slag remains unclear. This study indicated that the coupling effects of DOM and microbes governed the geochemical behaviour of HMs in slag. These findings provide new insights into how organic amendments impact the geochemical behaviour of HMs in slag, contributing to the development of phytostabilization technology.

Leaching Characteristics of Heavy Metals in the Baghouse Filter Dust from Direct-Fired Thermal Desorption of Contaminated Soil

After thermal desorption, the total amount of heavy metals (HMs) is enriched in baghouse filter dust. To further understand the related environmental impact, the leaching characteristics under various conditions must be explored. Therefore, this study aimed to examine the leaching characteristics of seven HMs in the dust generated in the direct-fired thermal desorption process and to compare the differences in heavy metal leaching characteristics in the soil before and after thermal desorption. The leaching characteristics and bioaccessibility of seven HMs-arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb), nickel (Ni), and zinc (Zn)-were analyzed in dust and in soil before and after thermal desorption. The activity of HMs in dust was strong. Therefore, environmental effects and effects on human health should be considered in the treatment of soil and dust after thermal desorption.

Biochar-seeded struvite precipitation for simultaneous nutrient recovery and chemical oxygen demand removal in leachate: From laboratory to pilot scale

Refuse transfer station (RTS) leachate treatment call for efficient methods to increase nutrient recovery (NH4+−N and PO43−−P) and chemical oxygen demand (COD) removal. In this study, the effects of various operational factors (seeding dose, pH, initial NH4+-N concentration, and reaction time) on biochar-seeded struvite precipitation were investigated at laboratory and pilot scales. Mealworm frass biochar (MFB) and corn stover biochar (CSB) were used as seeding materials to compare with traditional seed struvite. The maximum NH4+−N and PO43−−P recover efficiency of the MFB-seeded process reached 85.4 and 97.5%, higher than non-seeded (78.5 and 88.0%) and CSB-seeded (80.5 and 92.0%) processes and close to the struvite-seeded (84.5 and 95.1%) process. The MFB-seeded process also exhibited higher COD removal capacity (46.4%) compared to CSB-seeded (35.9%) and struvite-seeded (31.2%) processes and increased the average particle size of the struvite product from 33.7 to 70.2 μm for better sustained release. XRD, FT-IR, and SEM confirmed the orthorhombic crystal structure with organic matter attached to the struvite product. A pilot-scale test was further carried out in a custom-designed stirred tank reactor (20 L). In the pilot-scale test, the MFB-seeded process still spectacularly recovered 77.9% of NH4+−N and 96.1% of PO43−−P with 42.1% COD removal, which was slightly lower than the laboratory test due to insufficient and uniform agitation. On the whole, MFB-seeded struvite precipitation is considered to be a promising pretreatment method for rural RTS leachate.