Xiaoqiang Cui

Capacity and mechanisms of ammonium and cadmium sorption on different wetland-plant derived biochars

The objective of this study was to investigate the relationship between Cd(2+)/NH4(+) sorption and physicochemical properties of biochars produced from different wetland plants. Biochars from six species of wetland plants (i.e., Canna indica, Pennisetum purpureum Schum, Thalia dealbata, Zizania caduciflora, Phragmites australis and Vetiveria zizanioides) were obtained at 500°C and characterized, and their sorption for ammonium and cadmium was determined. There were significant differences in elemental composition, functional groups and specific surface area among the biochars derived from different wetland plant species. Sorption of ammonium and cadmium on the biochars could be described by a pseudo second order kinetic model, and the simple Langmuir model fits the isotherm data better than the Freundlich or Temkin model. The C. indica derived biochar had the largest sorption capacity for NH4(+) and Cd(2+), with a maximum sorption of 13.35 and 125.8mgg(-1), respectively. P. purpureum Schum derived biochar had a similar maximum sorption (119.3mgg(-1)) for Cd(2+). Ammonium sorption was mainly controlled by cation exchange, surface complexation with oxygen-containing functional groups and the formation of magnesium ammonium phosphate compounds, whereas for Cd(2+) sorption, the formation of cadmium phosphate precipitates, cation exchange and binding to oxygen-containing groups were the major possible mechanisms. In addition, the sorption of ammonium and cadmium was not affected by surface area and microporosity of the biochars.

Potential mechanisms of cadmium removal from aqueous solution by Canna indica derived biochar

The objective of this study was to investigate the mechanisms of cadmium (Cd) sorption on biochars produced at different temperature (300-600°C) and their quantitative contribution. The sorption isotherms and kinetics of Cd(2+) sorption on biochars were determined and fitted to different models. The Cd(2+) sorption data could be well described by a simple Langmuir model, and the pseudo second order kinetic model best fitted the kinetic data. The maximum sorption capacity (Qm) obtained from the Langmuir model for CIB500 was 188.8mgg(-1), which was greater than that of biochars produced at other temperature. Precipitation with minerals, ion exchange, complexation with surface oxygen-containing functional groups, and coordination with π electrons were the possible mechanisms of Cd(2+) sorption on the biochars. The contribution of each mechanism varied with the pyrolysis temperature. With increasing pyrolysis temperature, the contribution of surface complexation and metal ion exchange decreased from 24.5% and 43.3% to 0.7% and 4.7%, while the contribution of precipitation and Cd(2+)-π interaction significantly increased from 29.7% and 2.5% to 89.5% and 5.1%, respectively. Overall, the precipitation with minerals and metal ion exchange dominated Cd(2+) sorption on the biochars (accounted for 73.0-94.1%), and precipitation with minerals was the primary mechanism of Cd(2+) sorption on the high-temperature biochars (≥500°C) (accounted for 86.1-89.5%).

Removal of phosphate from aqueous solution using magnesium-alginate/chitosan modified biochar microspheres derived from Thalia dealbata.

The objective of this study was to determine the feasibility of using magnesium-alginate/chitosan modified biochar microspheres to enhance removal of phosphate from aqueous solution. The introduction of MgCl2 substantially increased surface area of biochar (116.2m(2)g(-1)), and both granulation with alginate/chitosan and modification with magnesium improved phosphate sorption on the biochars. Phosphate sorption on the biochars could be well described by a simple Langmuir model, and the MgCl2-alginate modified biochar microspheres exhibited the highest phosphate sorption capacity (up to 46.56mgg(-1)). The pseudo second order kinetic model better fitted the kinetic data, and both the Yoon-Nelson and Thomas models were superior to other models in describing phosphate dynamic sorption. Precipitation with minerals and ligand exchange were the possible mechanisms of phosphate sorption on the modified biochars. These results imply that MgCl2-alginate modified biochar microspheres have potential as a green cost-effective sorbent for remediating P contaminated water environment.

Pyrolysis of wetland biomass waste: Potential for carbon sequestration and water remediation.

Management of biomass waste is crucial to the efficiency and sustainable operation of constructed wetlands. In this study, biochars were prepared using the biomass of 22 plant species from constructed wetlands and characterized by BET-N2 surface area analysis, FTIR, TGA, SEM, EDS, and elemental compositions analysis. Biochar yields ranged from 32.78 to 49.02%, with mesopores dominating the pore structure of most biochars. The biochars had a R50 recalcitrance index of class C and the carbon sequestration potential of 19.4-28%. The aquatic plant biomass from all the Chinese constructed wetlands if made into biochars has the potential to sequester 11.48 Mt carbon yr(-1) in soils over long time periods, which could offset 0.4% of annual CO2 emissions from fossil fuel combustion in China. In terms of adsorption capacity for selected pollutants, biochar derived from Canna indica plant had the greatest adsorption capacity for Cd(2+) (98.55 mg g(-1)) and NH4(+) (7.71 mg g(-1)). Whereas for PO4(3-), Hydrocotyle verticillata derived biochar showed the greatest adsorption capacities (2.91 mg g(-1)). The results from this present study demonstrated that wetland plants are valuable feedstocks for producing biochars with potential application for carbon sequestration and contaminant removal in water remediation.

Impact of different feedstocks derived biochar amendment with cadmium low uptake affinity cultivar of pak choi (Brassica rapa ssb. chinensis L.) on phytoavoidation of Cd to reduce potential dietary toxicity

Biochar has become eco-friendly amendment used for phytoavoidation with low cadmium (Cd) accumulating cultivars of crops to ensure food safety in Cd contaminated soils. In this study, biochar with different waste feedstock material were evaluated for their effectiveness on essential trace metals mobility, Cd bioavailability and its accumulation in two contrasting Cd accumulating cultivars of pak choi (Brassica rapa ssp. chinensis L.) grown in Cd contaminated Mollisol soil. A greenhouse experiment was conducted with plants grown in Cd contaminated soil that had been amended with biochar derived from barley straw, tomato green waste, chicken manure, duck manure and swine manure at application rate of 0%, 2.5% and 5.0% (w/w). The results showed that soil pH was significantly increased by all treatments. Biochar increased plant dry biomass, micronutrients bioavailability with significant differences in the Cd sorption capacity, with the effectiveness higher with increasing biochar application rate. However, tomato green waste (TGW) and chicken manure (CM) derived biochar were more effective than the other biochar in reducing Cd mobilization in soil by 35-54% and 26-43% and reduced its accumulation in shoots of pak choi cultivars by 34-76% and 33-72% in low Cd accumulator cultivar and 64-85% and 55-80% in high Cd accumulator cultivar than the control. Overall, results indicate that TGW and CM biochar can efficiently immobilize Cd, thereby reducing bioavailability in Cd contaminated Mollisol soil to ensure food safety.

Cow manure and cow manure-derived biochar application as a soil amendment for reducing cadmium availability and accumulation by Brassica chinensis L. in acidic red soil

Abstract Organic amendment is a promising, in situ phytostabilization approach to alleviate the phytotoxic effects of heavy metal contaminated soils. The aim of this study was to evaluate the feasibility of cow manure (CM) and its derived biochar (CMB) as a soil amendment on cadmium (Cd) availability and accumulation in low and high Cd-accumulating cultivars of Brassica chinensis L. grown in an acidic red soil. CM and CMB were applied to Cd-contaminated acidic red soil at the rates of 0, 3.0 and 6.0% (w/w). Application of CMB was significantly more effective than that of CM, as it reduced the availability of Cd in soil by 34.3-69.9% and its bioaccumulation in the low Cd accumulator, Aijiaoheiye 333, by 51.2 and 67.4%, respectively. The addition of CMB significantly increased the extractability and accumulation of trace metals (Zn, Mn, Fe, and Cu) by plants and improved plant biomass production. CMB application, combined with utilizing low Cd accumulating cultivars represents a new, sustainable strategy to alleviate the toxic effects on Cd and improve food safety.

Effect of humic acid amendment on cadmium bioavailability and accumulation by pak choi (Brassica rapa ssp. chinensis L.) to alleviate dietary toxicity risk

ABSTRACT Cadmium (Cd) contamination in soil and its movement into food chain through vegetable dietary poses a risk to human health. A pot experiment was conducted to investigate the effect of humic acid (HA) and two cultivars of Brassica rapa ssp. chinensis L. (pak choi) with differing Cd accumulation abilities on Cd accumulation in different Cd contaminated Ferralsol, Histosol and Luvisol soils. The results showed that HA significantly increased soil pH and cation exchange capacity in Ferralsol (acidic) and Histosol (neutral) soils. HA was more effective in Ferralsol and Histosol soil in reducing bioavailable Cd and its accumulation in both cultivars. Low and high Cd accumulating cultivars combined with HA effectively reduced shoot Cd concentration by 7–34% and 19–35% in Histosol soil, whereas 22–34% and 11–26% in Ferralsol soil, respectively. However, no such reduction was observed for Cd accumulation and bioavailability in Cd-contaminated Luvisol (alkaline) soil. Application of HA enhanced shoot dry biomass in both cultivars grown in Histosol and Ferralsol soils. Therefore, the HA amendment combination with low Cd accumulating cultivars of pak choi could be an effective method for phytostabilization and reduce health risks associated with consuming this vegetable grown in Cd-contaminated acidic and neutral pH soils.