Properties and heavy metal leaching characteristics of leachate sludge‐derived biochar

Abstract

Heavy metals and metalloids, in sludge and sediments, are environmental pollutants of concern with long-term negative effects on human and ecological health. In this study, sludge from biological treatment of municipal waste leachate was pyrolyzed into leachate sludge-derived biochar (LSDB) at 300 C to 900 C, comprising complex organic and inorganic (particularly heavy metals) species formed from heterogeneous chemical reactions. Based on different advanced material analyses, that is, Thermogravimetric Analysis (TGA), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), and X-ray diffraction (XRD) analysis, this study revealed that mass loss and microstructural changes of LSDBs occurred primarily due to decomposition of volatiles, aromatic rings, carbonates, and hydroxides. The leaching behaviors of heavy metals from LSDBs were evaluated using the Synthetic Precipitation Leaching Procedure (SPLP). The final pH in SPLP increased from 7.5 to 12.5 with pyrolysis temperature. The pH increase favored the retention of heavy metals in the LSDBs due to the formation of low soluble precipitates at alkaline pH. The heavy metals and metalloids in the LSDBs were present as surface precipitates due to precipitation and cation exchange rather than surface complexation. The leaching contents of metals and metalloids, such as Cr, Cd, Ni, Pb, and As, were all below their respective maximum discharge standards for the first priority pollutants in China. Practitioner Points• The pH increase favored the retention of heavy metals in the leachate sludge-derived biochar (LSDB).• The heavy metals in the LSDB were present as surface precipitates due to precipitation and cation exchange rather than surface complexation.• The heavy metals/metalloids concentration of LSDB (>600 C) in leachate was low and was likely safe for use.

Addressing Heavy Metal Pollution in Nigeria: Evaluating Policies, Assessing Impacts, and Enhancing Remediation Strategies

“…Biochar possesses unique physicochemical properties, such as abundant oxygencontaining functional groups, high porosity, and large specific surface areas, which make it an effective material for remediation processes (Zhang et al, 2021;Liang et al, 2023). Low-carbon remediation strategies aim to reduce greenhouse gas emissions while promoting sustainable development in the context of heavy metal pollution remediation ((O'Brien et al, 2021).…”

Biochar as Alternative Material for Heavy Metal Adsorption from Groundwaters: Lab-Scale (Column) Experiment Review

“…Furthermore, with respect to the possible leaching of weighed metals from biochar, Zhang et al [261] explained that the pollutants, both organic and inorganic, already present in the feedstocks remain immobilised within the solid matrix thanks to pyrolysis. In fact, through this thermal convection process, the aromatic structure formed allows for heavy metals to be strongly bonded to the biochar [262].…”

Removal and Adsorption Mechanisms of Phosphorus, Cd and Pb from Wastewater Conferred by Landfill Leachate Sludge-Derived Biochar

“…At the same time, LLSDBs with high pyrolysis temperatures released extra CO 2 , which underwent secondary reactions with carbon atoms in the LLSDBs, thereby opening pores that were closed and increasing porosity [28,29]. However, when the pyrolysis temperature was greater than 600 • C, the aggregation and accumulation of micropores reduced the specific surface area of biochars and reduced thermal stability [30,31]. Therefore, LLSDB600 was selected for subsequent research.…”

“…OH − reacted with Cd(II) and Pb(II) in the wastewater to generate the substances Cd(OH) 2 , Pb(OH) 2 , and Cd(OH) 2 ; Pb(OH) 2 was also prone to react with CO 2 in the air to generate CdCO 3 , PbCO 3 , and Cd(II), and Pb(II) could also react with CO 3 2− (CaCO 3 ionized to generate Ca 2+ and CO 3 2− in the wastewater) to generate CdCO 3 and PbCO 3 . The mainly chemical reactions associated were as follows [31,47]:…”