Xinde Cao

Properties of dairy-manure-derived biochar pertinent to its potential use in remediation

Conversion of waste products into biochar (BC) is being considered as one of several waste disposal and recycling options. In this study, we produced BC from dairy manures by heating at low temperatures (500 degrees C) and under abundant air condition. The resultant BC was characterized for physical, chemical, and mineralogical properties specifically related to its potential use in remediation. The BC from all manures behaved similarly. Surface area, ash content, and pH of the BC increased as temperature increased, while yield decreased with increasing temperature. The BC was rich in mineral elements such as N, Ca, Mg, and P in addition to C, and concentrations of C and N decreased with increasing temperature as a result of combustion and volatilization; while P, Ca, and Mg increased as temperature increased. For example, C significantly decreased from 36.8% at 100 degrees C to 1.67% at 500 degrees C; whereas P increased from 0.91% to 2.66%. Water soluble P, Ca, and Mg increased when heated to 200 degrees C but decreased at higher temperatures likely due to increased crystallization of Ca-Mg-P, as supported by the formation of whitlockite (Ca,Mg)(3)(PO(4))(2) following 500 degrees C treatment. The presence of whitlockite was evidenced by X-ray diffraction analysis. Quartz and calcite were present in all BC produced. The BC showed appreciable capability of adsorption for Pb and atrazine from aqueous solution, with Pb and atrazine removal by as high as 100% and 77%, respectively. The results indicated that dairy manure can be converted into biochar as an effective adsorbent for application in environmental remediation.

Removal of heavy metals from aqueous solution by biochars derived from anaerobically digested biomass.

This study examined the ability of two biochars converted from anaerobically digested biomass to sorb heavy metals using a range of laboratory sorption and characterization experiments. Initial evaluation of DAWC (digested dairy waste biochar) and DWSBC (digested whole sugar beet biochar) showed that both biochars were effective in removing a mixture of four heavy metals (Pb(2 +), Cu(2+), Ni(2+), and Cd(2+)) from aqueous solutions. Compared to DAWC, DWSBC demonstrated a better ability to remove Ni and Cd. Further investigations of lead sorption by the two biochars indicated that the removal was mainly through a surface precipitation mechanism, which was confirmed by batch sorption experiments, mathematical modeling, and examinations of lead-laden biochars samples using SEM-EDS, XRD, and FTIR. The lead sorption capacity of the two biochars was close to or higher than 200mmol/kg, which is comparable to that of commercial activated carbons.

Biochar derived from anaerobically digested sugar beet tailings: Characterization and phosphate removal potential

Two biochars were produced from anaerobically digested and undigested sugar beet tailings through slow-pyrolysis at 600°C. The digested sugar beet tailing biochar (DSTC) and raw sugar beet tailing biochar (STC) yields were around 45.5% and 36.3% of initial dry weight, respectively. Compared to STC, DSTC had similar pH and surface functional groups, but higher surface area, and its surface was less negatively charged. SEM-EDS and XRD analyses showed that colloidal and nano-sized periclase (MgO) was presented on the surface of DSTC. Laboratory adsorption experiments were conducted to assess the phosphate removal ability of the two biochars, an activated carbon (AC), and three Fe-modified biochar/AC adsorbents. The DSTC showed the highest phosphate removal ability with a removal rate around 73%. Our results suggest that anaerobically digested sugar beet tailings can be used as feedstock materials to produce high quality biochars, which could be used as adsorbents to reclaim phosphate.

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>Cu>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 [Pb(10)(PO(4))(6)F(2)], 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).

Simultaneous Immobilization of Lead and Atrazine in Contaminated Soils Using Dairy-Manure Biochar

Biochar produced from waste biomass is increasingly being recognized as a green, cost-effective amendment for environmental remediation. This work was to determine the ability of biochar to immobilize heavy metal Pb and organic pesticide atrazine in contaminated soils. Biochar prepared from dairy manure was incubated with contaminated soils at rates of 0, 2.5, and 5.0% by weight for 210 d. A commercial activated carbon (AC) was included as a comparison. The AC was effective in immobilizing atrazine, but was ineffective for Pb. However, biochar was effective in immobilizing both atrazine and Pb and the effectiveness was enhanced with increasing incubation time and biochar rates. After 210 d, soils treated with the highest rate of 5.0% biochar showed more than 57% and 66% reduction in Pb and atrazine concentrations in 0.01 M CaCl(2) extraction, respectively. Lead and atrazine concentrations in the toxicity characteristic leaching procedure solutions were reduced by 70-89% and 53-77%, respectively. Uptake of Pb and atrazine by earthworms (Eisenia fetida) was reduced by up to 79% and 73%. Phosphorus originally contained in biochar reacted with soil Pb to form insoluble hydroxypyromorphite Pb(5)(PO(4))(3)(OH), as determined by X-ray diffraction, which was presumably responsible for soil Pb immobilization, whereas atrazine stabilization may result from its adsorption by biochar demonstrated by the significant exponential decrease of extractable atrazine with increasing organic C in biochar (r(2) > 0.97, p < 0.05). The results highlighted the potential of dairy-manure biochar as a unique amendment for immobilization of both heavy metal and organic contaminants in cocontaminated soils.

Removal of phosphate from aqueous solution by biochar derived from anaerobically digested sugar beet tailings.

Biochar converted from agricultural residues or other carbon-rich wastes may provide new methods and materials for environmental management, particularly with respect to carbon sequestration and contaminant remediation. In this study, laboratory experiments were conducted to investigate the removal of phosphate from aqueous solution by biochar derived from anaerobically digested sugar beet tailings (DSTC). Batch adsorption kinetic and equilibrium isotherm experiments and post-adsorption characterizations using SEM-EDS, XRD, and FTIR suggested that colloidal and nano-sized MgO (periclase) particles on the biochar surface were the main adsorption sites for aqueous phosphate. Batch adsorption experiments also showed that both initial solution pH and coexisting anions could affect the adsorption of phosphate onto the DSTC biochar. Of the mathematical models used to describe the adsorption kinetics of phosphate removal by the biochar, the Ritchie N_th-order (N=1.14) model showed the best fit. Two heterogeneous isotherm models (Freundlich and Langmuir-Freundlich) fitted the experimental isotherm of phosphate adsorption onto the biochar better than the Langmuir adsorption model. Our results suggest that biochar converted from anaerobically digested sugar beet tailings is a promising alternative adsorbent, which can be used to reclaim phosphate from water or reduce phosphate leaching from fertilized soils. In addition, there is no need to regenerate the exhausted biochar because the phosphate-laden biochar contains abundance of valuable nutrients, which may be used as a slow-release fertilizer to enhance soil fertility and to sequester carbon.

Immobilization of Zn, Cu, and Pb in contaminated soils using phosphate rock and phosphoric acid

Considerable research has been done on P-induced Pb immobilization in Pb-contaminated soils. However, application of P to soils contaminated with multiple heavy metals is limited. The present study examined effectiveness of phosphoric acid (PA) and/or phosphate rock (PR) in immobilizing Pb, Cu, and Zn in two contaminated soils. The effectiveness was evaluated using water extraction, plant uptake, and a simple bioaccessibility extraction test (SBET) mimicking metal uptake in the acidic environment of human stomach. The possible mechanisms for metal immobilization were elucidated using X-ray diffraction, scanning electron microscopy, and chemical speciation program Visual MINTEQ. Compared to the control, all P amendments significantly reduced Pb water solubility, phytoavailability, and bioaccessibility by 72-100%, 15-86%, and 28-92%, respectively. The Pb immobilization was probably attributed to the formation of insoluble Pb phosphate minerals. Phosphorus significantly reduced Cu and Zn water solubility by 31-80% and 40-69%, respectively, presumably due to their sorption on minerals (e.g., calcite and phosphate phases) following CaO addition. However, P had little effect on the Cu and Zn phytoavailability; while the acid extractability of Cu and Zn induced by SBET (pH 2) were even elevated by up to 48% and 40%, respectively, in the H(3)PO(4) treatments (PA and PR+PA). Our results indicate that phosphate was effective in reducing Pb availability in terms of water solubility, bioaccessibility, and phytoavailability. Caution should be exercised when H(3)PO(4) was amended to the soil co-contaminated with Cu and Zn since the acidic condition of SBET increased Cu and Zn bioaccessibility though their water solubility was reduced.

Effects of compost and phosphate amendments on arsenic mobility in soils and arsenic uptake by the hyperaccumulator, Pteris vittata L.

Chinese brake fern (Pteris vittata L.), an arsenic (As) hyperaccumulator, has shown the potential to remediate As-contaminated soils. This study investigated the effects of soil amendments on the leachability of As from soils and As uptake by Chinese brake fern. The ferns were grown for 12 weeks in a chromated-copper-arsenate (CCA) contaminated soil or in As spiked contaminated (ASC) soil. Soils were treated with phosphate rock, municipal solid waste, or biosolid compost. Phosphate amendments significantly enhanced plant As uptake from the two tested soils with frond As concentrations increasing up to 265% relative to the control. After 12 weeks, plants grown in phosphate-amended soil removed >8% of soil As. Replacement of As by P from the soil binding sites was responsible for the enhanced mobility of As and subsequent increased plant uptake. Compost additions facilitated As uptake from the CCA soil, but decreased As uptake from the ASC soil. Elevated As uptake in the compost-treated CCA soil was related to the increase of soil water-soluble As and As(V) transformation into As(III). Reduced As uptake in the ASC soil may be attributed to As adsorption to the compost. Chinese brake fern took up As mainly from the iron-bound fraction in the CCA soil and from the water-soluble/exchangeable As in the ASC soil. Without ferns for As adsorption, compost and phosphate amendments increased As leaching from the CCA soil, but had decreased leaching with ferns when compared to the control. For the ASC soil, treatments reduced As leaching regardless of fern presence. This study suggest that growing Chinese brake fern in conjunction with phosphate amendments increases the effectiveness of remediating As-contaminated soils, by increasing As uptake and decreasing As leaching.

A review of biochar as a low-cost adsorbent for aqueous heavy metal removal

ABSTRACT As a low-cost adsorbent, biochar can be used as a low-cost adsorbent for wastewater treatment, particularly with respect to treating heavy metals in wastewater. A number of studies have demonstrated effective removal of heavy metals from aqueous solutions by biochar and, in some cases, proven the superiority of biochars to activated carbons. Among several factors affecting the sorption ability of biochars, feedstock materials play a significant role. This review incorporates existing literature to understand the overall sorption behavior of heavy metals on biochar adsorbents. Depending on the biochar type, heavy metal can be removed by different mechanisms such as complexation, physical sorption, precipitation and electrostatic interactions. Mathematical sorption models can be used to understand the efficiency of biochar at removing heavy metals, and promote the application of biochar technology in water treatment.

Field assessment of lead immobilization in a contaminated soil after phosphate application

A pilot-scale field demonstration was conducted at a Pb-contaminated site to assess the effectiveness of Pb immobilization using P amendments. The test site was contaminated by past battery recycling activities, with average soil Pb concentration of 1.16%. Phosphate amendments were applied at a 4.0 molar ratio of P/Pb with three treatments: T1, 100% P from H(3)PO(4); T2, 50% from H(3)PO(4)+50% from Ca(H(2)PO(4))(2); and T3, 50% from H(3)PO(4)+5% phosphate rock. Soil samples were collected and characterized 220 days after P application. Surface soil pH was reduced from 6.45 to 5.05 in T1, to 5.22 in T2, and to 5.71 in T3. Phosphate treatments effectively transformed up to 60% of total soil Pb from the non-residual fraction (sum of water soluble and exchangeable, carbonate, Fe-Mn oxide, and organic fractions) to the residual fraction relative to the control. In addition, P treatments reduced Toxicity Characteristic Leaching Procedure (TCLP) Pb from 82 mg l(-1) to below EPAs regulatory level of 5 mg l(-1) in the surface soil. Scanning electron microscopy-energy dispersive X-ray elemental analysis and X-ray diffraction analysis indicated formation of insoluble chloropyromorphite [Pb(5)(PO(4))(3)Cl] mineral in the P-treated soils. Although H(3)PO(4) is necessary to dissolve meta-stable Pb in soil for further lead immobilization, it should be used with caution due to its potential secondary contamination. A mixture of H(3)PO(4) and Ca(H(2)PO(4))(2) or phosphate rock was effective in immobilizing Pb with minimum adverse impacts associated with pH reduction.