Sludge transforms into biochar: Doping calcium induces phosphorus transforming into a plant-available speciation

The mass-produced sewage sludge (SS) worldwide is regarded as an important phosphorus (P) pool with a P-content of 2-3% (dry basis). Pyrolytic conversion of SS into P-rich biochar has multiple environmental benefits: toxicity elimination, carbon sequestration and soil fertilization. It has been proved that P transforms into insoluble speciation such as Ca2P2O7 during pyrolysis, and this would be influenced significantly by inherent minerals such as Ca, Mg, Fe, Al, etc [1, 2]. With a purpose of enhancing biochar’s fertilizer efficiency to plant, we selected calcium (Ca) as an additive to SS and expected their thermal-chemical interaction would induce P transforming into a plant-available speciation. The sequential extraction experiments showed that after pyrolysis (biochar: SS500) the percent of the insoluble phosphates (HCl-extracted P) increased significantly from 8.28% to 76.6%, while the readily soluble P species being extracted by water, NaHCO3 and NaOH decreased sharply. Doping CaCl2 strengthened this transformation and the produced biochars at pyrolysis temperature of 500oC with 20% (w/w) Ca-doping (biochar: SS-Ca500) contained 84.1% insoluble phosphates and 5.28% Fe/Al mineral adsorbed P (NaOH-extracted P). It indicated that Ca could compete for more P than Fe/Al during pyrolysis. Instrumental analysis (XRD, NMR) showed that Ca promoted more formation of pyrophosphate and short-chain polyphosphates such as Ca5(PO4)3(OH), Ca5(PO4)3Cl, which are species facilitating plant-uptake while avoiding dissolution loss. This study gave an insight into P speciation transformation during biochar formation and suggested that P availability in biochars are controllable by doping minerals to structure a safe slow-release P fertilizer benefiting plant growth. Please click Additional Files below to see the full abstract

Mechanisms of Lead, Copper, and Zinc Retention by Phosphate Rock

The solid–liquid interface reaction between phosphate rock (PR) and metals (Pb, Cu, and Zn) was studied. Phosphate rock has the highest affinity for Pb, followed by Cu and Zn, with sorption capacities of 138, 114, and 83.2 mmol/kg PR, respectively. In the Pb–Cu–Zn ternary system, competitive metal sorption occurred with sorption capacity reduction of 15.2%, 48.3%, and 75.6% for Pb, Cu, and Zn, respectively compared to the mono-metal systems. A fractional factorial design showed the interfering effect in the order of Pb \u3e Cu \u3e Zn. Desorption of Cu and Zn was sensitive to pH change, increasing with pH decline, whereas Pb desorption was decreased with a strongly acidic TCLP extracting solution (pH=2.93). The greatest stability of Pb retention by PR can be attributed to the formation of insoluble fluoropyromorphite [Pb10(PO4)6F2], which was primarily responsible for Pb immobilization (up to 78.3%), with less contribution from the surface adsorption or complexation (21.7%), compared to 74.5% for Cu and 95.7% for Zn. Solution pH reduction during metal retention and flow calorimetry analysis both supported the hypothesis of retention of Pb, Cu, and Zn by surface adsorption or complexation. Flow calorimetry indicated that Pb and Cu adsorption onto PR was exothermic, while Zn sorption was endothermic. Our research demonstrated that PR can effectively remove Pb from solutions, even in the presence of other heavy metals (e.g. Cu, Zn). ‘‘Capsule’’: Phosphate-induced formation of fluoropyromorphite is primarily responsible for Pb immobilization by phosphate rock, whereas Cu and Zn retention is mainly attributable to the surface adsorption or complexation

Interactions of arsenic, copper, and zinc in soil-plant system:Partition, uptake and phytotoxicity

Arsenic, copper, and zinc are common elements found in contaminated soils but little is known about their combined effects on plants when presented simultaneously. Here, we systematically investigated the phytotoxicity and uptake of binary and ternary mixtures of As, Cu, and Zn in a soil-plant system, using wheat (Triticum aestivum) as model species. The reference models of concentration addition (CA) and response addition (RA) coupled with different expressions of exposure (total concentrations in soil ([M]tot, mg/kg), free ion activities in soil solution ({M}, μM), and internal concentrations in plant roots ([M]int, μg/g)), were selected to assess the interaction mechanisms of binary mixtures of As–Cu, As–Zn, and Cu–Zn. Metal(loid) interactions in soil were estimated in terms of solution-solid partitioning, root uptake, and root elongation effects. The partitioning of one metal(loid) between the soil solution and solid phase was most often inhibited by the presence of the other metal(loid). In terms of uptake, inhibitory effects and no effects were observed in the mixtures of As, Cu, and Zn, depending on the mixture combinations and the dose metrics used. In terms of toxicity, simple (antagonistic or synergistic) and more complex (dose ratio-dependent or dose level-dependent) interaction patterns of binary mixtures occurred, depending on the dose metrics selected and the reference models used. For ternary mixtures (As-Cu-Zn), nearly additive effects were observed irrespective of dose descriptors and reference models. The observed interactions in this study may help to understand and predict the joint toxicity of metal(loid)s mixtures in soil-plant system. Mixture interactions and bioavailability should be incorporated into the regulatory framework for accurate risk assessment of multimetal-contaminated sites

Mechanisms of lead, copper, and zinc retention by phosphate rock

Mitteilungen des Förderkreises Archive und Bibliotheken zur Geschichte der Arbeiterbewegung, Nr. 37 / März 2010. Ausführliche Rezension hier in der Tageszeitung junge welt vom Montag 29. März 2010

Interaction of Inherent Minerals with Carbon during Biomass Pyrolysis Weakens Biochar Carbon Sequestration Potential

Biomass carbon could be sequestrated in the form of biochar, an aromatized carbon structure produced by pyrolysis. Inherent minerals are reactive constituents that interact with organic contents during pyrolysis, significantly affecting the properties of the pyrolysis product. Despite their importance, their influence on biochar–carbon sequestration has been rarely studied. For this study four types of biomass were selected: barley grass, peanut hull, cow manure, and sewage sludge to investigate the influence of inherent minerals on carbon conversion during pyrolysis. Results showed removal of inherent minerals shifts the peak biomass conversion to a higher temperature (370 °C) compared to that of biomass with inherent minerals being present (330 °C). It also led to reduced emissions of low-molecular-weight organic compounds. Compared to pristine biomass, more carbon (3.5–30.1%) could be retained in biochar along pyrolysis after removing inherent minerals. And it showed increased resistance to chemical and thermal oxidation decomposition, indicating higher carbon stability and therefore carbon sequestration potential. Instrumental analysis showed removal of inherent minerals facilitated disappearance of oxygen-containing functional groups such as CO, OC–O, and C–O, while promoting C–C/CC bonds, indicating higher aromatization of biochars. This study suggested that removing minerals prior to pyrolysis can be a promising approach for strengthening carbon-sequestration potential of biochar

A sustainable biochar catalyst synergized with copper heteroatoms and CO2 for singlet oxygenation and electron transfer routes

We have developed a wood waste-derived biochar as a sustainable graphitic carbon catalyst for environmental remediation through catalytic pyrolysis under the synergistic effects between Cu heteroatoms and CO2, which for the first time are found to significantly enhance the oxygen functionalities, defective sites, and highly ordered sp2-hybridized carbon matrix. The copper-doped graphitic biochars (Cu-GBCs) were further characterized by XRD, FTIR, Raman, XPS, etc., revealing that the modified specific surface area, pore structure, graphitization, and active sites (i.e., defective sites and ketonic group) on the Cu-GBCs corresponded to the synergistic Cu species loading and Cu-induced carbon-matrix reformation in CO2 environment during pyrolysis. The catalytic ability of Cu-GBCs was evaluated using the ubiquitous peroxydisulfate (PDS) activation system for the removal of various organic contaminants (i.e., rhodamine B, phenol, bisphenol A, and 4-chlorophenol), and gave the highest degradation rate of 0.0312 min-1 in comparison with those of pristine GBCs and N2-pyrolyzed Cu-GBCs ranging from 0.0056 to 0.0094 min-1. The synergistic effects were attributed to the encapsulated Cu heteroatoms, evolved ketonic groups, and abundant unconfined π electrons within the carbon lattice. According to scavenger experiments, ESR analysis, and two-chamber experiments, selective and sustainable non-radical pathways (i.e., singlet oxygenation and electron transfer) mediated by the Cu-induced metastable surface complex were achieved in the Cu-GBC/PDS system. This study offers the first insights into the efficacy, sustainability, and mechanistic roles of Cu-GBCs as an emerging carbon-based catalyst for green environmental remediation

Potassium doping increases biochar carbon sequestration potential by 45%, facilitating decoupling of carbon sequestration from soil improvement

Abstract Negative emissions technologies offer an important tool to limit the global warming to <2 °C. Biochar is one of only a few such technologies, and the one at highest technology readiness level. Here we show that potassium as a low-concentration additive in biochar production can increase biochar’s carbon sequestration potential; by up to 45% in this study. This translates to an increase in the estimated global biochar carbon sequestration potential to over 2.6 Gt CO2-C(eq) yr−1, thus boosting the efficiency of utilisation of limited biomass and land resources, and considerably improving the economics of biochar production and atmospheric carbon sequestration. In addition, potassium doping also increases plant nutrient content of resulting biochar, making it better suited for agricultural applications. Yet, more importantly, due to its much higher carbon sequestration potential, AM-enriched biochar facilitates viable biochar deployment for carbon sequestration purposes with reduced need to rely on biochar’s abilities to improve soil properties and crop yields, hence opening new potential areas and scenarios for biochar applications