Ran Xiao

Nutrient transformations during composting of pig manure with bentonite

This work aimed to evaluate the influence of different amounts of bentonite on nutrients transformation during pig manure composting process. The results showed that bentonite had no significant effects on compost temperature and pH changes. While, EC, moisture, OM, TN and NO(3)(-)-N were notably influenced by BT addition. The adding of BT could facilitate OM degradation, increase TKN content and decrease the C/N ratio. Increasing the proportion of bentonite in pig manure compost to reduce extractable heavy metal content is feasible. However, potherb mustard seed GI decreased with the proportion of added bentonite increasing. The results suggest that a proportion of less than 2.5% bentonite is recommended for addition to pig manure compost, and examining the additive ratio in a comprehensive waste composting project is a worthwhile direction for future research.

Soil heavy metal contamination and health risks associated with artisanal gold mining in Tongguan, Shaanxi, China

Soil contamination with heavy metals due to mining activities poses risks to ecological safety and human well-being. Limited studies have investigated heavy metal pollution due to artisanal mining. The present study focused on soil contamination and the health risk in villages in China with historical artisanal mining activities. Heavy metal levels in soils, tailings, cereal and vegetable crops were analyzed and health risk assessed. Additionally, a botany investigation was conducted to identify potential plants for further phytoremediation. The results showed that soils were highly contaminated by residual tailings and previous mining activities. Hg and Cd were the main pollutants in soils. The Hg and Pb concentrations in grains and some vegetables exceeded tolerance limits. Moreover, heavy metal contents in wheat grains were higher than those in maize grains, and leafy vegetables had high concentrations of metals. Ingestion of local grain-based food was the main sources of Hg, Cd, and Pb intake. Local residents had high chronic risks due to the intake of Hg and Pb, while their carcinogenic risk associated with Cd through inhalation was low. Three plants (Erigeron canadensis L., Digitaria ciliaris (Retz.) Koel., and Solanum nigrum L.) were identified as suitable species for phytoremediation.

Recent developments in biochar utilization as an additive in organic solid waste composting: A review

In recent years, considerable studies have been devoted to investigating the effect of biochar application on organic solid waste composting. This review provides an up-to-date overview of biochar amendment on composting processes and compost quality. Biochar production, characteristics, and its application coupled with the basic concepts of composting are briefly introduced before detailing the effects of biochar addition on composting. According to recent studies, biochar has exhibited great potential for enhancing composting. It is evident that biochar addition in composting can: (1) improve compost mixture physicochemical properties, (2) enhance microbial activities and promote organic matter decomposition, (3) reduce ammonia (NH3) and greenhouse gas (GHG) emissions, and (4) upgrade compost quality by increasing the total/available nutrient content, enhancing maturity, and decreasing phytotoxicity. Despite that, further research is needed to explore the mechanism of biochar addition on composting and to evaluate the agricultural and environmental performances of co-composted biochar compost.

Facilitative capture of As(V), Pb(II) and methylene blue from aqueous solutions with MgO hybrid sponge-like carbonaceous composite derived from sugarcane leafy trash

Enhancing the contaminant adsorption capacity is a key factor affecting utilization of carbon-based adsorbents in wastewater treatment and encouraging development of biomass thermo-disposal. In this study, a novel MgO hybrid sponge-like carbonaceous composite (HSC) derived from sugarcane leafy trash was prepared through an integrated adsorption-pyrolysis method. The resulted HSC composite was characterized and employed as adsorbent for the removal of negatively charged arsenate (As(V)), positively charged Pb(II), and the organic pollutant methylene blue (MB) from aqueous solutions in batch experiments. The effects of solution pH, contact time, initial concentration, temperature, and ionic strength on As(V), Pb(II) and MB adsorption were investigated. HSC was composed of nano-size MgO flakes and nanotube-like carbon sponge. Hybridization significantly improved As(V), Pb(II) and methylene blue (MB) adsorption when compared with the material without hybridization. The maximum As(V), Pb(II) and MB adsorption capacities obtained from Langmuir model were 157u202fmg/g, 103u202fmg/g and 297u202fmg/g, respectively. As(V) adsorption onto HSC was best fit by the pseudo-second-order model, and Pb(II) and MB with the intraparticle diffusion model. Increased temperature and ionic strength decreased Pb(II) and MB adsorption onto HSC more than As(V). Further FT-IR, XRD and XPS analysis demonstrated that the removal of As(V) by HSC was mainly dominated by surface deposition of MgHAsO4 and Mg(H2AsO4)2 crystals on the HSC composite, while carbon π-π* transition and carbon π-electron played key roles in Pb(II) and MB adsorption. The interaction of Pb(II) with carbon matrix carboxylate was also evident. Overall, MgO hybridization improves the preparation of the nanotube-like carbon sponge composite and provides a potential agricultual residue-based adsorbent for As(V), Pb(II) and MB removal.

Degradation of Orange G by Fenton-like reaction with Fe-impregnated biochar catalyst

This study was conducted to evaluate the catalytic activity of Fe-impregnated sugarcane biochar (FSB) for removing azo dye Orange G (OG) from solution under various Fenton-like oxidation conditions. The optimum molar Fe concentration for impregnation to achieve maximum catalytic activity of FSB in Fenton-like reaction with acceptable effluent Fe release was 0.25u202fM (163.4u202fFeu202fmg/g in FSB). High removal efficiency of 99.7% was achieved within 2u202fh of reaction at optimum conditions of 0.075u202fg/L H2O2, 0.5u202fg/L FSB for 0.1u202fg/L OG at initial pH 5.5 under 25u202f°C. For every 10u202f°C increase, the time for maximum OG degradation efficiency decreased by 0.5u202fh. The OG removal by FSB exhibited a slow induction reaction followed by fast OG decomposition. FSB can be used successively for at least 4 runs with >89.3% OG removal. The FSB was more economical, efficient, and recyclable than other conventional Fenton oxidation catalysts.

Effect of pyrolysis temperature on phosphate adsorption characteristics and mechanisms of crawfish char

The purpose of this study was to investigate the characteristics of crawfish char (CFC) derived at different pyrolysis temperature and to evaluate its adsorption characteristics on phosphate. Phosphate adsorption by CFC occurred rapidly at the beginning of the reaction, and the time to reach equilibrium was dependent on the pyrolysis temperature. Maximum adsorption capacities of phosphate by CFC at different pyrolysis temperatures were high in order of CFC800 (70.9u202fmg/g)u202f>u202fCFC600 (56.8u202fmg/g)u202f>u202fCFC400 (47.2u202fmg/g)u202f≫u202fCFC200 (9.5u202fmg/g)u202f≈u202funcharred crawfish feedstock (CF) (7.1u202fmg/g). Spectroscopic analyses using SEM-EDS and FTIR showed that the phosphate present in the CFC itself was associated with carbon, while the phosphate adsorbed on the CFC was closely related to calcium. The adsorption of phosphate by CFC is dominantly affected by pH. Phosphate adsorption of CFC600 primarily occurred at acid and neutral pH which is related to dissolved calcium from surface and phosphate hydrolysis product (H2PO4-), while phosphate adsorption of CFC800 mainly took place at alkaline pH, with precipitation mechanism between PO43- and calcium dissolved from free CaO and Ca(OH)2. Overall, CFC derived at pyrolysis temperatures above 400u202f°C is effective for waste reduction and phosphate treatment in wastewater.

Enhanced sorption of hexavalent chromium [Cr(VI)] from aqueous solutions by diluted sulfuric acid-assisted MgO-coated biochar composite

Metal oxide-Carbon composites have aroused great interesting towards specific anionic contaminants removal from the polluted environment. In this study, aiming at removing toxic chromate ion [Cr(VI)] from aqueous solutions, a novel approach was developed to produce surface-enhanced MgO-coated biochar adsorbent from sugarcane harvest residue (SHR). It was found that sulfuric acid hydrolysis and MgO-coating both facilitated the removal of Cr(VI) by biochars, and the maximum sorption capacities for the pristine biochar (SHR550), MgO-coated biochar (MgSHR550), and acid-assisted MgO-coated biochar (MgASHR550) that derived from the Langmuir isotherm model were 20.79, 54.64, and 62.89u202fmgu202fg-1, respectively. Additionally, the Cr(VI) removal was a pseudo-second-order kinetic model controlled process with equilibrium reached within 24u202fh. The mechanism investigation revealed that Cr(VI) ions was directly sorbed by the MgO-coated biochars via the chemical interaction between MgO and Cr(VI), whereas the sorption-coupled reduction of Cr(VI) to Cr(III) governed the sorption of Cr(VI) on the SHR550. Although the increases of solution pH (>2.0) and KNO3 concentration (>0.05u202fmolu202fL-1) reduced the Cr(VI) removal by biochars, while there were lower secondary pollution risks in MgO-coated biochar treatments due to the suppressed release of Cr(III) in solutions. This work could provide guidance for the production of efficient biochar for the removal of Cr(VI) from wastewater.

Mercury adsorption in the Mississippi River deltaic plain freshwater marsh soil of Louisiana Gulf coastal wetlands

Mercury adsorption characteristics of Mississippi River deltaic plain (MRDP) freshwater marsh soil in the Louisiana Gulf coast were evaluated under various conditions. Mercury adsorption was well described by pseudo-second order and Langmuir isotherm models with maximum adsorption capacity of 39.8u202fmgu202fg-1. Additional fitting of intraparticle model showed that mercury in the MRDP freshwater marsh soil was controlled by both external surface adsorption and intraparticle diffusion. The partition of adsorbed mercury (mg g-1) revealed that mercury was primarily adsorbed into organic-bond fraction (12.09) and soluble/exchangeable fraction (10.85), which accounted for 63.5% of the total adsorption, followed by manganese oxide-bound (7.50), easily mobilizable carbonate-bound (4.53), amorphous iron oxide-bound (0.55), crystalline Fe oxide-bound (0.41), and residual fraction (0.16). Mercury adsorption capacity was generally elevated along with increasing solution pH even though dominant species of mercury were non-ionic HgCl2, HgClOH and Hg(OH)2u202fat between pH 3 and 9. In addition, increasing background NaCl concentration and the presence of humic acid decreased mercury adsorption, whereas the presence of phosphate, sulfate and nitrate enhanced mercury adsorption. Mercury adsorption in the MRDP freshwater marsh soil was reduced by the presence of Pb, Cu, Cd and Zn with Pb showing the greatest competitive adsorption. Overall the adsorption capacity of mercury in the MRDP freshwater marsh soil was found to be significantly influenced by potential environmental changes, and such factors should be considered in order to manage the risks associated with mercury in this MRDP wetland for responding to future climate change scenarios.

High-efficiency removal of Pb(II) and humate by a CeO2–MoS2 hybrid magnetic biochar

This work prepares a novel CeO2-MoS2 hybrid magnetic biochar (CMMB) for the adsorptive removal of Pb(II) and humate from aqueous solution. The CMMB was evaluated against magnetic biochar (MB). The results showed that CMMB exhibited strong magnetic separation ability. Hybridization of CMMB greatly improved Pb(II) and humate removal compared to MB, with >99% Pb(II) and humate removed within 6u202fh. Pb(II) and humate removal capacities of CMMB were 263.6u202fmg/g and 218.0u202fmg/g, respectively, with negligible influence of ion strength in the range of 0-0.1u202fmol/L NaNO3. Pb(II) removal mechanism involved predominately with electrostatic attraction, Cπ-Pb(II) bond interaction, and surface adsorption and complexation combined processes; while pore-filling, partition effect and π-π interaction contributed to the adsorption of humate. Overall, the introduction of graphene-like MoS2 materials into biochar benefits both of the biomass resources recovery and environmental protection.