Converting food waste into soil amendments for improving soil sustainability and crop productivity: A review.

One-third of the annual food produced globally is wasted and much of the food waste (FW) is unutilized; however, FW can be valorized into value-added industrial products such as biofuel, chemicals, and biomaterials. Converting FW into soil amendments such as compost, vermicompost, anaerobic digestate, biofertilizer, biochar, and engineered biochar is one of the best nutrient recovery and FW reuse approaches. The soil application of FW-based amendments can improve soil fertility, increase crop production, and reduce contaminants by altering soil's chemical, physical, microbial, and faunal properties. However, the efficiency of the amendment for improving ecosystem sustainability depends on the type of FW, conversion method, application rate, soil type, and crop type. Engineered biochar/biochar composite materials produced using FW have been identified as promising amendments for soil remediation, reducing commercial fertilizer usage, and increasing soil nutrient use efficiency. The development of quality standards and implementation of policies and regulations at all stages of the food supply chain are necessary to manage (reduce and re-use) FW.

Designer biochar with enhanced functionality for efficient removal of radioactive cesium and strontium from water.

Radioactive elements released into the environment by accidental discharge constitute serious health hazards to humans and other organisms. In this study, three gasified biochars prepared from feedstock mixtures of wood, chicken manure, and food waste, and a KOH-activated biochar (40% food waste + 60% wood biochar (WFWK)) were used to remove cesium (Cs+) and strontium (Sr2+) ions from water. The physicochemical properties of the biochars before and after adsorbing Cs+ and Sr2+ were determined using X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectroscopy, extended X-Ray absorption fine structure (EXAFS) spectroscopy, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX). The WFWK exhibited the highest adsorption capacity for Cs+ (62.7 mg/g) and Sr2+ (43.0 mg/g) among the biochars tested herein. The removal of radioactive 137Cs and 90Sr exceeded 80% and 47%, respectively, in the presence of competing ions like Na+ and Ca2+. The functional groups present in biochar, including -OH, -NH2, and -COOH, facilitated the adsorption of Cs+ and Sr2+. The Cs K-edge EXAFS spectra revealed that a single coordination shell was assigned to the Cs-O bonding at 3.11 Å, corresponding to an outer-sphere complex formed between Cs and the biochar. The designer biochar WFWK may be used as an effective adsorbent to treat radioactive 137Cs- and 90Sr-contaminated water generated during the operation of nuclear power plants and/or unintentional release, owing to the enrichment effect of the functional groups in biochar via alkaline activation.

Biochar alters chemical and microbial properties of microplastic-contaminated soil.

The occurrence of microplastics (MPs) in soils can negatively affect soil biodiversity and function. Soil amendments applied to MP-contaminated soil can alter the overall soil properties and enhance its functions and processes. However, little is known about how soil amendments improve the quality of MP-contaminated soils. Thus, the present study used a microcosm experiment to explore the potential effects of four types of biochar on the chemical and microbial properties of low-density polyethylene (LDPE) MP-contaminated soil under both drought and well-watered conditions. The results show that the biochars altered soil pH, electrical conductivity (EC), available phosphorous, and total exchangeable cations (TEC) with some variability depending on the biochar type. Oilseed rape straw (OSR)-derived biochars increased soil pH, EC, and TEC under both water conditions with the highest values of 7.94, 0.54 dS m-1 and 22.0 cmol(+) kg-1, respectively. Soil enzyme activities varied under all treatments; in particular, under drought conditions, the fluorescein diacetate activity increased in soils with high temperature (700 °C) biochar. The application of soft wood pellet biochar (700 °C) to MP-contaminated soil increased urease activity by 146% under well-watered conditions. OSR-derived biochars significantly reduced soil acid phosphatase activity under both water conditions. With biochar supplementation, the diversity indices of the bacterial community increased in well-watered soil but not in soil under drought conditions. The abundance of bacterial phyla, such as Firmicutes, Proteobacteria, Actinobacteria, Dictyoglomi, and Gemmatimonadetes, was relatively high in all treatments. Biochar application resulted in negligible variations in bacterial communities under drought conditions but significant variations under well-watered conditions. The findings of this study imply that biochar can be used as a soil amendment to improve the overall soil quality of MP-contaminated soil, but its impact varies depending on the pyrolysis feedstock and temperature. Thus, selecting a suitable biochar is important for improving the soil quality in MP-contaminated soils.

Fe(III) loaded chitosan-biochar composite fibers for the removal of phosphate from water.

Excess phosphorous (P) in aquatic systems causes adverse environmental impacts including eutrophication. This study fabricated Fe(III) loaded chitosan-biochar composite fibers (FBC-N and FBC-C) from paper mill sludge biochar produced under N2 (BC-N) and CO2 (BC-C) conditions at 600 °C for adsorptive removal of phosphate from water. Investigations using SEM/EDX, XPS, Raman spectroscopy, and specific surface area measurement revealed the morphological and physico-chemical characteristics of the adsorbent. The Freundlich isotherm model well described the phosphate adsorption on BC-N, while the Redlich-Peterson model best fitted the data of three other adsorbents. The maximum adsorption capacities were 9.63, 8.56, 16.43, and 19.24 mg P g-1 for BC-N, BC-C, FBC-N, and FBC-C, respectively, indicating better adsorption by Fe(III) loaded chitosan-biochar composite fibers (FBCs) than pristine biochars. The pseudo-first-order kinetic model suitably explained the phosphate adsorption on BC-C and BC-N, while data of FBC-N and FBC-C followed the pseudo-second-order and Elovich model, respectively. Molecular level observations of the P K-edge XANES spectra confirmed that phosphate associated with iron (Fe) minerals (Fe-P) were the primary species in all the adsorbents. This study suggests that FBCs hold high potential as inexpensive and green adsorbents for remediating phosphate in contaminated water, and encourage resource recovery via bio-based management of hazardous waste.

Effects of field scale in situ biochar incorporation on soil environment in a tropical highly weathered soil.

Biochar has been proven as a soil amendment to improve soil environment. However, mechanistic understanding of biochar on soil physical properties and microbial community remains unclear. In this study, a wood biochar (WB), was incorporated into a highly weathered tropical soil, and after 1 year the in situ changes in soil properties and microbial community were evaluated. A field trial was conducted for application of compost, wood biochar, and polyacrylamide. Microstructure and morphological features of the soils were characterized through 3D X-ray microscopy and polarized microscopy. Soil microbial communities were identified through next-generation sequencing (NGS). After incubation, the number of pores and connection throats between the pores of biochar treated soil increased by 3.8 and 7.2 times, respectively, compared to the control. According to NGS results, most sequences belonged to Anaerolinea thermolimosa, Caldithrix palaeochoryensis, Chthoniobacter flavus, and Cohnella soli. Canonical correlation analysis (CCA) further demonstrated that the microbial community structure was determined by inorganic N (IN), available P (AP), pH, soil organic C (SOC), porosity, bulk density (BD), and aggregate stability. The treatments with co-application of biochar and compost facilitated the dominance of Cal. palaeochoryensis, Cht. flavus, and Coh. soli, all of which promoted organic matter decomposition and ammonia oxidation in the soil. The apparent increases in IN, AP, porosity, and SOC caused by the addition of biochar and compost may be the proponents of changes in soil microbial communities. The co-application of compost and biochar may be a suitable strategy for real world biochar incorporation in highly weathered soil.

Effects of aging and weathering on immobilization of trace metals/metalloids in soils amended with biochar.

Biochar is an effective amendment for trace metal/metalloid (TMs) immobilization in soils. The capacity of biochar to immobilize TMs in soil can be positively or negatively altered due to the changes in the surface and structural chemistry of biochar after soil application. Biochar surfaces are oxidized in soils and induce structural changes through physical and biochemical weathering processes. These changes in the biochar surface and structural chemistry generally increase its ability to immobilize TMs, although the generation of dissolved black carbon during weathering may increase TM mobility. Moreover, biochar modification can improve its capacity to immobilize TMs in soils. Over the short-term, engineered/modified biochar exhibited increased TM immobilization capacity compared with unmodified biochar. In the long-term, no large distinctions in such capacities were seen between modified and unmodified biochars due to weathering. In addition, artificial weathering at laboratories also revealed increased TM immobilization in soils. Continued collection of mechanistic evidence will help evaluate the effect of natural and artificial weathering, and biochar modification on the long-term TM immobilization capacity of biochar with respect to feedstock and synthesis conditions in contaminated soils.

Carbon dioxide capture in biochar produced from pine sawdust and paper mill sludge: Effect of porous structure and surface chemistry.

The CO2 concentration in the atmosphere is increasing and threatening the earth's climate. Selective CO2 capture at large point sources will help to reduce the CO2 emissions to the atmosphere. Biochar with microporous structure could be a potential material to capture CO2. The impact of feedstock type, pyrolysis temperature and steam activation of biochars were evaluated for CO2 adsorption capacity. Pine sawdust biochars were produced at 550 °C, and steam activated for 45 min at the same temperature after completing the pyrolysis (PS550 and PSS550). Paper mill sludge biochars were produced at 300 and 600 °C (PMS300 and PMS600). The CO2 adsorption capacity of biochars was tested at 25 °C using a volumetric sorption analyzer. Pine sawdust biochars showed significantly higher CO2 adsorption capacity than paper mill sludge biochars due to high surface area and microporosity. Pine sawdust biochars were then evaluated for dynamic adsorption under representative post-combustion flue gas concentration conditions (15% CO2, 85% N2) using a breakthrough rig. Both materials showed selective CO2 uptake over N2 which is the major component along with CO2 in flue gas. PSS550 had slightly higher CO2 adsorption capacity (0.73 mmol g^-1 vs 0.67 mmol g^-1) and CO2 over N2 selectivity (26 vs 18) than PS550 possibly due to increase of microporosity, surface area, and oxygen containing basic functional groups through steam activation. Pine sawdust biochar is an environmentally friendly and low-cost material to capture CO2.

Gasification biochar from biowaste (food waste and wood waste) for effective CO2 adsorption.

Biochar is newly proposed as an innovative and cost-effective material to capture CO2. In this study, biochar was produced from feedstock mixtures of food waste and wood waste (i.e., 20%:80% WFW20, 30%:70% WFW30 and 40%:60% WFW40) by gasification. The two biochar adsorbents containing the highest percentage of food waste, i.e., WFW40-K and WFW40-KC, were activated by KOH and KOH + CO2, respectively. The biochar adsorbents were then tested for CO2 adsorption at room temperature of 25 °C by using a volumetric sorption analyzer. The WFW20 showed the highest CO2 adsorption capacity, while higher percentage of food waste in the feedstock was unfavorable for the CO2 adsorption. The presence of N and S on the biochar surface was the primary contributor to the high CO2 uptake on WFW20. The development of micropores by KOH activation significantly increased the CO2 adsorption on WFW40-K, but KOH + CO2 activation could not further increase the development of micropores and subsequent CO2 adsorption. Moreover, WFW40-K showed >99% recyclability during 10 consecutive adsorption-desorption cycles. The biochars derived from biowaste (food waste and wood waste) could be effective adsorbents for CO2 capture by providing green solution for food waste recycling.

Sustainable removal of Hg(II) by sulfur-modified pine-needle biochar.

Sulfur-modified pine-needle biochar (BC-S) was produced for the removal of Hg(II) in aqueous media via post-pyrolysis S stream exposure. Fourier-transform infrared spectroscopy, elemental analysis, and X-ray photoelectron spectroscopy confirmed the addition of S(0) groups on the surface of BC-S. Hg(II) adsorption on BC-S was best described by the Freundlich isotherm with a KF of 21.0 mg L g-1 and a pseudo-second-order adsorption kinetics model with a rate of 0.35 g mg-1 min-1. Hg(II) removal on BC-S was found to be an endothermic process that relied on C-Hg and S-Hg interactions rather than reduction by S(0) groups. The adsorption increased with increasing solution pH and decreased with increasing dissolved organic matter concentration, but was unaffected by increasing salt concentrations. BC-S showed a maximum of 3 % S leaching in aqueous media after 28-d exposure time, and exposure to aqueous media did not convert Hg(II) to elemental Hg. Overall, BC-S exhibited superior Hg(II) removal performance over unmodified BC, thus having potential applications in natural water and wastewater treatment with no significant threat of secondary pollution.

Recent advances in mitigating membrane biofouling using carbon-based materials.

Biofouling is the Achilles Heel of membrane processes. The accumulation of organic foulants and growth of microorganisms on the membrane surface reduce the permeability, shorten the membrane life, and increase the energy consumption. Advancements in novel carbon-based materials (CBMs) present significant opportunities in mitigating biofouling of membrane processes. This article provides a comprehensive review of the recent progress in the application of CBMs in antibiofouling membrane. It starts with a detailed summary of the different antibiofouling mechanisms of CBM-containing membrane systems. Next, developments in membrane modification using CBMs, especially carbon nanotubes and graphene family materials, are critically reviewed. Further, the antibiofouling potential of next-generation carbon-based membranes is surveyed. Finally, the current problems and future opportunities of applying CBMs for antibiofouling membranes are discussed.

Biochar-induced metal immobilization and soil biogeochemical process: An integrated mechanistic approach.

The nature of biochar-derived dissolved organic matter (DOM) has a crucial role in the interactions between biochar and metal immobilization, carbon dynamics, and microbial communities in soil. This study utilized excitation-emission matrix coupled with parallel factor analysis (EEM-PARAFAC) modeling to provide mechanistic evidence of biochar-induced influences on main soil biogeochemical processes. Three biochars produced from rice straw, wood, and grass residues were added to sandy and sandy loam soils and incubated for 473 d. Microbial and terrestrial humic-like fluorescent components were identified in the soils after incubation. The sandy loam soil exhibited a higher DOM with microbial sources than did the sandy soil. All biochars reduced Pb bioavailability, whereas the rice straw biochar enhanced the As bioavailability in the sandy loam soil. The biochar-derived aliphatic-DOM positively correlated with As bioavailability (r = 0.82) in the sandy loam soil and enhanced the cumulative CO2-C (r = 0.59) in the sandy soil. The promoted cumulative CO2-C in the sandy soil with all biochars correlated with the enhanced microbial communities, in particular, gram-positive (r = 0.59) and gram-negative (r = 0.59) bacteria. Our results suggest that the integration of EEM-PARAFAC with spectroscopic indices could be useful for a comprehensive interpretation of the soil quality changes in response to the application of biochar.

Distribution characteristics of Cd in different types of leaves of Festuca arundinacea intercropped with Cicer arietinum L.: A new strategy to remove pollutants by harvesting senescent and dead leaves.

Although cost-effective, phytoremediation is too expensive when considering the large-scale pollution. Relative to harvesting the whole plant, it is more practicable to remove and dispose of senescent and dead leaves after phytoremediation. The phytoremediation efficiency of Festuca arundinacea for Cd was evaluated in this study, because over about 7% of the land area in China was contaminated with Cd. The accumulation, redistribution, and extraction of Cd were evaluated in different leaves of F. arundinacea intercropped with N-fixing species at different densities (Cicer arietinum L). The results showed that coordinate and malposed intercropping systems increased the dry weight of the senescent and dead leaves of F. arundinacea by 30-41% and 103-168% compared to the monoculture system, respectively. More Cd was redistributed to the senescent and dead leaves of F. arundinacea under both intercropping systems. Occupying only 22-30% of the total leaf biomass, senescent and dead leaves accumulated 74-88% of leaf Cd under different cultivation conditions. Relative to the monoculture system, intercropping decreased the amount of time needed to reduce soil Cd by 44-53%. The biomass production and Cd accumulation of F. arundinacea were higher in the malposed intercropping system, and it had higher remediation efficiency than the coordinate intercropping system. This study demonstrated that intercropping, especially malposed intercropping of F. arundinacea and C. arietinum L., is a practicable technology for leaf harvesting phytoremediation.

Effects of elevated CO2 on the phytoremediation efficiency of Noccaea caerulescens.

Concentrations of atmospheric carbon dioxide have been continuously increasing, and more investigations are needed in regard to the responses of various plants to the corresponding climatic conditions. In particular, potential variations in phytoremediation efficiency induced by global warming have rarely been investigated. Objective of this research was to evaluate the changes in phytoremediation efficiency of Noccaea caerulescens exposed to different concentrations of CO2. The concentrations of CO2 in the elevated CO2 treatments were adjusted to 550 ±â€¯50 ppm to match the level of atmospheric CO2 predicted in 2050-2070. Compared to ambient controls (400 ppm), biomass yields and metal concentrations of N. caerulescens increased under elevated CO2 conditions, thus indicating that the phytoremediation efficiency of the species could increase in higher CO2 environment. In addition, water soluble and exchangeable Pb and Cu concentrations in soils decreased under elevated CO2 conditions, which reduced the leaching risks of the metals. The concentrations of malondialdehyde (MDA) of N. caerulescens decreased to different degrees with the increased CO2 concentrations. The overall findings suggested that elevations in CO2 can reduce the oxidative damage caused by metals in this species. The phytoremediation efficiency of N. caerulescens grown in multiple metal-enriched soils could be enhanced with global warming.

Heavy metal dissolution mechanisms from electrical industrial sludge.

In this paper, we investigate the release of heavy metals from sludge produced from an electrical industry using both organic and inorganic acids. Single and sequential extractions were conducted to assess heavy metals in different phases of the sludge. Metal release from sludge was investigated in the presence of three inorganic acids (nitric, sulfuric, and phosphoric) and three organic acids (acetic, malic, and citric) at concentrations ranging from 0.1 to 2.0 mol L-1. Sequential extraction indicated the presence of Cu primarily in the carbonate fraction, Pb in the residual fraction, and Ni in the FeMn oxide fraction. The cumulative release rates of heavy metals (i.e., Pb, Cu, and Ni) by 1.0 mol L-1 of acid increased with the use of the following acids in the order of: malic < sulfuric < acetic < phosphoric < citric < nitric. Acetic acid exhibited the highest release of Cu, at a rate of 72.62 × 10-11 mol m-2 s-1 at pH 1, and malic acid drove the release of Pb at a maximum rate of 3.90 × 10-11 mol m-2 s-1. Meanwhile, nitric acid provided the maximum rate of Ni release (0.23 × 10-11 mol m-2 s-1) at pH 1. The high rate of metal release by organic acids is explained through ligand-promoted mechanisms that enhance the release of metal ions from the sludge. The results from our study emphasize that an understanding of the metal release mechanism is key to selecting the optimal acid for the maximum recovery of heavy metals.

Biochar-supported nZVI (nZVI/BC) for contaminant removal from soil and water: A critical review.

The promising characteristics of nanoscale zero-valent iron (nZVI) have not been fully exploited owing to intrinsic limitations. Carbon-enriched biochar (BC) has been widely used to overcome the limitations of nZVI and improve its reaction with environmental pollutants. This work reviews the preparation of nZVI/BC nanocomposites; the effects of BC as a supporting matrix on the nZVI crystallite size, dispersion, and oxidation and electron transfer capacity; and its interaction mechanisms with contaminants. The literature review suggests that the properties and preparation conditions of BC (e.g., pore structure, functional groups, feedstock composition, and pyrogenic temperature) play important roles in the manipulation of nZVI properties. This review discusses the interactions of nZVI/BC composites with heavy metals, nitrates, and organic compounds in soil and water. Overall, BC contributes to the removal of contaminants because it can attenuate contaminants on the surface of nZVI/BC; it also enhances electron transfer from nZVI to target contaminants owing to its good electrical conductivity and improves the crystallite size and dispersion of nZVI. This review is intended to provide insights into methods of optimizing nZVI/BC synthesis and maximizing the efficiency of nZVI in environmental cleanup.

Effect of biochars pyrolyzed in N2 and CO2, and feedstock on microbial community in metal(loid)s contaminated soils.

Little is known about the effects of applying amendments on soil for immobilizing metal(loid)s on the soil microbial community. Alterations in the microbial community were examined after incubation of treated contaminated soils. One soil was contaminated with Pb and As, a second soil with Cd and Zn. Red pepper stalk (RPS) and biochars produced from RPS in either N2 atmosphere (RPSN) or CO2 atmosphere (RPSC) were applied at a rate of 2.5% to the two soils and incubated for 30 days. Bacterial communities of control and treated soils were characterized by sequencing 16S rRNA genes using the Illumina MiSeq sequencing. In both soils, bacterial richness increased in the amended soils, though somewhat differently between the treatments. Evenness values decreased significantly, and the final overall diversities were reduced. The neutralization of pH, reduced available concentrations of Pb or Cd, and supplementation of available carbon and surface area could be possible factors affecting the community changes. Biochar amendments caused the soil bacterial communities to become more similar than those in the not amended soils. The bacterial community structures at the phylum and genus levels showed that amendment addition might restore the normal bacterial community of soils, and cause soil bacterial communities in contaminated soils to normalize and stabilize.

Soil lead immobilization by biochars in short-term laboratory incubation studies.

Exchangeable lead (Pb) extracted by ammonium acetate from three independent incubation studies was assessed to understand the influence of feedstock, pyrolysis temperatures, and production conditions on Pb immobilization capacities of different biochars. Vegetable waste biochar, pine cone, wood bark, cocopeat, red pepper stalk, and palm kernel shell were used as feedstocks (food supply and agricultural wastes) to produce biochars at 200-650 °C with and without N2/CO2. Biochars were applied at 5 and 2.5% (w w-1) to a Pb contaminated (i.e., 1445 mg kg-1) agricultural soil collected near an old mine. Lead immobilization in biochar treated soils at the end of incubation period was normalized per gram of biochar applied. Biochar produced from vegetable waste at 500 °C showed the highest Pb immobilization (87%) and highest total exchangeable cations (13.5 cmol(+) kg-1) at the end of the 45 d incubation period. However, on the basis of Pb immobilization per gram of biochar, red pepper stalk biochar produced in CO2 at 650 °C was the best in Pb immobilization (0.09 mg kg-1 g-1 biochar) compared to the other biochars. The enhanced ability to immobilize Pb by biochar produced in CO2 could be due to the presence of siloxanes (SiOSi) on biochar surface. Pearson correlation analysis revealed that alkaline pH, ash%, and N% of biochars influence in Pb immobilization and exchangeable cation availability in soil. Biochar production atmosphere considerably change its properties that influence Pb immobilization. Further studies are needed on the modification of properties and Pb immobilization by biochars produced from various feedstocks in CO2.

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.

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.