Unraveling natural aging-induced properties change of sludge-derived hydrochar and enhanced cadmium sorption site heterogeneity

Abstract

Hydrochar has potential applications in soil improvement and heavy metal remediation. Hydrochar would undergo the process of aging when introduced into the soil, altering its properties. However, recent studies have focused mainly on the artificial aging of hydrochar, which could not reveal the cumulative effect of multiple environmental factors. Therefore, the periodical monitoring of the property and sorption behavior of hydrochar after amending soils is necessary to better understand the multifaceted mechanisms associated with the natural aging of hydrochar. This study selected the sludge-derived hydrochar (SLHC) as a typical hydrochar and applied a 16-month rice–wheat–rice rotation to mimic the natural aging of hydrochar, focusing on changing properties and cadmium (Cd) sorption and literature contrast between aging strategies and biochar types. The porosity, O abundance, and ash content of 16-month aged SLHC increased by 37%, 47%, and 8.5%, respectively, facilitating Cd sorption due to surface complexation, pore sorption, and precipitation. The sorption percentage of Cd to SLHC was in the range of 11–14% for SLHC-A0 and increased to 17–31% for SLHC-A4 and 20–32% for SLHC-A16 after natural aging. The natural aging of SLHC induced by ash content played an essential role in Cd sorption site heterogeneity. Linear regression analysis showed that aging strategies on sorption behavior significantly differed between biochars. Thus, studies involving natural aging with multiple environmental factors are preferred over those involving chemical or biological aging. Future studies should continue to explore the mechanisms of natural aging-induced heavy metal sorption between hydrochar and pyrochar. These results improve insights to appraise the potential of SLHC as soil amendments to alleviate the adverse effects of heavy metal contamination and provide an essential basis for researchers and staff in soil management and environmental prevention. Graphical Abstract

Formable porous biochar loaded with La-Fe(hydr)oxides/montmorillonite for efficient removal of phosphorus in wastewater: process and mechanisms

“…In constrast, the σ e ⁎ was comparable between La 0.3 Fe 0.1 /MB and MCB 13 (Li et al 2021). The heterogeneous sorption sites originate from the defect structure, disordered arrangement, and grafting functional groups of carbonaceous materials, described with σ e * (Shen et al 2015;Wang et al 2022). Overall, the Fe/La(hydr)oxides-loaded would introduce more high-energy sorption sites, thereby strengthening the interaction between P and La 0.3 Fe 0.1 /MB and increasing its removal.…”

“…The adsorption capacity was determined and the equilibrium data were fitted to Langmuir and Freundlich isotherm models (Additional file 1: Text S2) as described in the literature (Qiu et al 2017). Meanwhile, we further studied the site energy distribution deduced from the Langmuir model based on an assumption of the distribution of site energies (Reguyal and Sarmah, 2018;Wang et al 2022). See the Additional file 1: Text S3 for details.…”

“…Due to the complex surface topography of biochar, the adsorption sites on the surface of biochar are uneven, and the location energy of these adsorption sites is different (Wang et al 2022). The area with high surface energy becomes the adsorption center of environmental pollutants, playing an important role in the adsorption process (Li et al 2021).…”

Hydrochar and Its Dissolved Organic Matter Aged in a 30-Month Rice–Wheat Rotation System: Do Primary Aging Factors Alter at Different Stages?

“…The findings demonstrate that hydrochar and its DOM continue to produce or enhance various beneficial properties in hydrochar-amended soils, even after soil aging, such as improved soil fertility, enhanced soil water retention, and increased soil carbon sequestration. For instance, the decomposition of labile components and the formation of hydrochar-mineral complexes can enhance the stability of hydrochar, aiding carbon sequestration. , More hydrophilic oxygen-containing functional groups in aged hydrochar can improve the water retention and fertility of soil and help immobilize toxic metals within the soil. , The enhanced stability of aged hydrochar can mitigate soil carbon emissions and facilitate carbon sequestration . Changes in HDOM properties (higher aromaticity and good hydrophilicity) also significantly affect pollutant transport within the soil. , However, this study has some limitations.…”

“…34,35 More hydrophilic oxygen-containing functional groups in aged hydrochar can improve the water retention and fertility of soil and help immobilize toxic metals within the soil. 26,66 The enhanced stability of aged hydrochar can mitigate soil carbon emissions and facilitate carbon sequestration. 67 Changes in HDOM properties (higher aromaticity and good hydrophilicity) also significantly affect pollutant transport within the soil.…”