Avanthi Deshani Igalavithana

Removal of hexavalent chromium in aqueous solutions using biochar : chemical and spectroscopic investigations

Biochar is an emerging low-cost sorbent used for removing trace metals from water. In this study, we evaluated the removal potential of aqueous hexavalent chromium (Cr(VI)) by biochars produced from soybean (Glycinemax L.) and burcucumber (Sicyos angulatus L.) residues. The highest Cr(VI) removal from solution occurred at low pH values (pH2-5), and adsorption decreased approximately tenfold when the pH increased from 2 to 10. Synchrotron-based X-ray absorption spectroscopy (XAS) investigations showed that Cr(VI) species were reduced to trivalent chromium (Cr(III)) at the biochar surface following Cr(VI) adsorption. Linear combination fitting (LCF) of X-ray absorption near edge structure (XANES) data indicated that approximately 90% of the total Cr(VI) (962μM) was reduced to Cr(III). Extended X-ray absorption fine structure (EXAFS) fitting results yielded interatomic chromium (CrCr) distances consistent with the formation of Cr(III) precipitates as Cr(OH)3. Trivalent chromium is far less soluble than Cr(VI) and typically precipitates as amorphous Cr(III) solids. Thus, biochars produced by soybean and burcucumber residues are a promising technique for both adsorbing and reductively immobilizing Cr(VI) from aqueous solutions.

Advances and future directions of biochar characterization methods and applications

ABSTRACT Biochar is a carbon-rich by-product of the thermal conversion of organic feedstocks and is primarily used as a soil amendment. Identification and quantification of biochar properties are important to ensure optimal outcomes for agricultural or environmental applications. Advanced spectroscopic techniques have recently been adopted in biochar characterization. However, biochar characterization approaches rely entirely on the users choice and accessibility to the new technology. The selection of proper methods is vital to accurately and consistently assess biochar properties. This review critically evaluates current biochar characterization methods of proximate, ultimate, physicochemical, surface and structural analyses, and important biochar properties for various applications.

Sulphamethazine in poultry manure changes carbon and nitrogen mineralisation in soils

ABSTRACT Antibiotics are newly emerging organic pollutants in manure, soil, vegetables and water. Animal manure application might be leading to the accumulation of antibiotics in the farmland. However, the effect of sulphamethazine (SMZ) on the soil microbial community was scarcely investigated. This study was aimed to evaluate the impact of SMZ on poultry manure, on the structure and function of microbial community, carbon mineralisation, and changes in nitrogen forms in soil via an incubation experiment lasting 56 d. The treatments consisted of poultry manure at 1% wt (PM), PM containing 20 mg kg−1 SMZ (PM + 20SMZ) and PM containing 100 mg kg−1 SMZ (PM + 100SMZ), along with the untreated soil (control). Solid phase extraction was performed to measure the SMZ concentration in soils using high-pressure liquid chromatography. The cumulative CO2-C was increased in all treated soils over the incubation period compared to the control. The PM + 100SMZ had the highest increase in cumulative CO2-C from the soil at 56 d of incubation. The treatment of PM + 20SMZ showed a short-term decrease in nitrification rate in the soils at 1 d by altering the microbial community composition with 17% dissimilarity and decreasing the abundance of bacteria compared to PM-treated soil. The PM + 100SMZ increased C mineralisation in the soil.

Characterization of bioenergy biochar and its utilization for metal/metalloid immobilization in contaminated soil

This study is a comparison of the effect of biochar produced by bioenergy systems, via the pyrolysis and gasification processes, on the immobilization of metals/metalloids in soil. Because the processes for these two techniques vary, the feedstocks undergo different heating regimens and, as a result, their respective char products exhibit different physico-chemical properties. Therefore, this study focuses on (1) the characterization of derivative biochar from the bioenergy system to understand their features and (2) an exploration of various biochar impacts on the mobility of As and Pb in contaminated soil. The results showed bioenergy biochars (BBCs) performed well in mitigating Pb extractability (1 M ammonium acetate) with a Pb immobilization >80%, but unfavorably mobilized the bioavailable As, likely because of electrostatic repulsion and ion exchange competition. The BBC surface functional group would chemically bond with the As and remain stable against the pH change. An increment in aromatic carbon would effectively enhance cation-π interaction for Pb immobilization. Nevertheless, an amendment with richer condensed structure and higher inorganic minerals (Ca2+, K+, Mg2+, and Na+) can lead to better performance in retaining Pb.

Metal(loid) immobilization in soils with biochars pyrolyzed in N2 and CO2 environments

Previous studies indicated that using CO2 as a reaction agent in the pyrolysis of biomass led to an enhanced generation of syngas via direct reaction between volatile organic carbons (VOCs) evolved from the thermal degradation of biomass and CO2. In addition, the physico-chemical properties of biochar in CO2 were modified. In this current study, biochars generated from red pepper stalks in N2 and CO2 (RPS-N and RPS-C, respectively) were tested for their effects on the immobilization of Pb, Cd, Zn, and As in contaminated soils. Soils were incubated for one month with 2.5% of RPS, and two biochars (i.e., RPS-N and RPS-C) at 25°C. After the incubation period soils were analyzed to determine the amendment effects on the behavior of metal(loid)s. The potential availability and mobility kinetics of metal(loid)s were assessed by single extraction of ammonium acetate and consecutive extraction of calcium chloride, respectively. Sequential extraction was used to further examine potential changes in geochemical fractions of metal(loid)s. The increased soil pH induced by application of the biochars reduced the potentially available Pb, Cd, and Zn, while RPS-C significantly reduced Pb due to the high surface area and aromaticity of RPS-C. However, RPS-C mobilized potentially available As compared to RPS-N due to the increased soil pH. Biochars reduced the mobility kinetics of Pb, Cd, and Zn, and RPS-N effectuated the greatest reduction of As mobility. The RPS-C increased the Fe and Mn oxides, hydroxide, and organically bound Pb, while both biochars and RPS-N increased residual Cd and Zn, and organically bound As, respectively. When considering the two biochars, RPS-C was highly effective for immobilization of Pb in soils, but it had no effect on Cd and Zn and a negative effect on As. In addition, RPS-C significantly increased the total exchangeable cations in soils.

Correction to: Determining soil quality in urban agricultural regions by soil enzyme-based index

Unfortunately, in the original publication of the article, Prof. Yang Sik Ok’s affiliation was incorrectly published. The author’s affiliation is as follows.

Determining soil quality in urban agricultural regions by soil enzyme-based index

Abstract Urban agricultural soils are highly variable, and careful selection of sensitive indicators is needed for the assessment of soil quality. This study is proposed to develop an index based on soil enzyme activities for assessing the quality of urban agricultural soils. Top soils were collected from urban agricultural areas of Korea, and soil chemical properties, texture, microbial fatty acids, and enzyme activities were determined. The soils belonged to five textural classes with the highest frequency of sandy loam. There was no clear correlation between the soil chemical properties and soil microbial properties. Principal component analysis (PCA) and factor analysis were applied to microbial groups for identification of microbial community variation in soils. Two soil groups, namely group 1 (G1) and group 2 (G2), based on microbial community abundance were examined by PCA, and those were more prominent in factor analysis. The G1 soils showed higher microbial community abundance than G2 soils. The canonical discriminant analysis was applied to the enzyme activities of sandy loam soil to develop an index, and the index validation was confirmed using the unused soils and published data. The high-quality soils in published literature assigned the high valued index. Microbial fatty acids and soil enzyme activities can be suitable indicators for soil quality evaluation of urban agricultural soils.

Potentially Toxic Element Contamination and Its Impact on Soil Biological Quality in Urban Agriculture: A Critical Review

The concept of urban agriculture is often used along with urbanization and industrialization. Around 15 % of global food production comes from urban lands, making urban soil quality a vital concern. Potentially toxic elements (PTEs) may contaminate urban soils through vehicle emissions, household waste, industrial effluents, and atmospheric depositions. Toxic metals, lead, nickel, zinc, copper, and chromium have been identified as the key PTEs that cause severe contaminations worldwide. Lead contamination is the most serious issue in many urbanized areas due to heavy traffic. High PTE concentrations in soils adversely affect microbial communities and enzyme activities, thereby degrading the biological soil quality and threatening the healthy food production in urban areas.