Biochar and enhanced phosphate capture: Mapping mechanisms to functional properties (original) (raw)
Related papers
ACS Sustainable Chemistry & Engineering
Biochars have been suggested to have P capture potential from effluent streams and to recycle the captured P to agricultural soils. However, most biochars have low P sorption capacity. The objective of this study was to engineer biochar for enhanced P sorption affinity. Biochar was produced from corn stover biomass pre-treated with FeSO4 (ISIB) using autothermal (air-blown) pyrolysis at 500 °C. Point of zero charge (pHZPC) shifted from 8.48 to 4.31, indicating that Fe treatment increased the dominance of acid functional groups. Batch equilibration isotherm study showed that ISIB had 11-12 times more P sorption capacity (3763 versus 46,300 mg kg-1 and 6704 versus 48,821 mg kg-1 for non-oxidized and oxidized conditions, respectively), while P desorption rate was ∼1/3 relative to the control biochar. A column leaching study also shows that ISIB was effective for removing P from simulated agricultural effluent. XRD (X-ray diffraction) and SEM-EDS (scanning electron microscopy-energy-dispersive X-ray spectrometry) analyses showed the P sorption was predominately through inner-sphere surface complexation followed by surface precipitation and that P is preferentially sorbed by hematite (α-Fe2O3) relative to magnetite (FeIII2O3 + FeIIO) or maghemite (γ-Fe2O3). This study demonstrates that ISIB can be produced by pyrolyzing corn stover with FeSO4, and the resulting ISIB is effective for adsorption and recycling of P. When loaded with P, the ISIB can potentially be used as a slow-release P fertilizer.
Reactivity of Fe-amended biochar for phosphorus removal and recycling from wastewater
PLOS Water
Using biochar to remove phosphorus (P) from wastewater has the potential to improve surface water quality and recycle recovered P as a fertilizer. In this research, effects of iron modification on P sorption behavior and molecular characterization on two different biochars and an activated carbon were studied. A biochar produced from cow manure anaerobic digest fibers (AD) pyrolyzed under NH3 gas had the greatest phosphate sorption capacity (2300 mg/kg), followed by the activated carbon (AC) (1500 mg/kg), and then the biochar produced from coniferous forest biomass (BN) (300 mg/kg). Modifying the biochars and AC with 2% iron by mass increased sorption capacities of the BN biochar to 2000 mg/kg and the AC to 2300 mg/kg, but decreased sorption capacity of the AD biochar to 1700 mg/kg. Molecular analysis of the biochars using P K-edge X-ray absorption near edge structure (XANES) spectroscopy indicated that calcium phosphate minerals were the predominant species in the unmodified biocha...
Particle Size- and Crystallinity-Controlled Phosphorus Release from Biochars
Energy & Fuels, 2019
Controlled-release sterile organic phosphorus fertilizers could be co-produced (as biochars) with 22 biofuels using the existing thermochemical conversion platforms. However, the availability of nutrient elements in biochar changes in amended soils, as a result of sizing (fragmentation) and 24 other biogeochemical processes. This study investigated particle size-(<38 vs. <600 m) and 25 pyrolysis temperature-dependent (200-800 °C in 100 °C intervals) phosphorus dissolution 26 kinetics (pH 8.5 NaHCO 3 over 18 d) of shrimp shell biochars. Two-dimensional infrared 27 correlation spectroscopy revealed an increase in P crystallinity (P-O functional group at 1043 28 cm-1) as a function of pyrolysis temperature and total P content of biochar. Broad and 29 symmetrical P-O peak in 700 °C biochar (but not at lower pyrolysis temperatures) was 30 attributable to semi-crystalline phosphate phases. Those thermodynamically stable P 31 phases in 700 °C biochar released higher orthophosphate concentration when pulverized to 32 smaller size fractions (<38 μm). Pyrolysis temperature-dependent phosphate release behaviors 33 (400 °C biochar >feedstock>700 °C biochar) indicated a complex interplay of solid-phase P 34 speciation, dissolved organic carbon concentration, and size-dependent reactivity involving the 35 colloidal fraction of phosphorus phases in biochars.
Potential effects of biochar on the availability of phosphorus — mechanistic insights
Geoderma, 2016
Potential supply shortages of phosphorus (P) rock reserves call for a more efficient use of P fertilizer and exploring new ways of recycling the nutrient within agro-ecosystems. Conditioning arable land with biochar might contribute to achieving both goals. We examined three putative mechanisms governing P availability in biochar amended soils. Potential direct P inputs from eight biochars differing in feedstocks and production techniques were assessed using sequential P fractionation. Phosphorus sorption on one pyrochar and one hydrochar was also studied. Finally, competitive sorption between P and biochar-derived dissolved organic matter (DOM) on goethite was studied at three pH levels. Total P varied from 0.6 to 4.0 mg P g −1 in biochars derived from phytomass, and was 47 mg P g −1 in a biochar derived from sewage sludge. In two slightly acidic hydrochars most P was 0.1 M NaOH extractable, Fe-associated, while in the remaining alkaline pyrochars most P was 1 M HCl extractable, Ca-associated. Biochar intrinsic P was mostly of intermediate stability and might slowly replenish labile P in soils. Both the pyrochar and the hydrochar studied were weak sorbents for phosphate. We show that DOM released from biochar, however, can inhibit P sorption on goethite depending on the initial pH, P to DOM ratio and order of sorbate addition. Strong competition between biochar-DOM and P for sorption sites on goethite especially at low pH values suggests that biochar-DOM might enhance P fertilizer use efficiency especially in acidic, highly weathered and strongly P fixing soils.
Biochar Phosphorus Sorption-Desorption: Potential Phosphorus Eutrophication Mitigation Strategy
Biochar - An Imperative Amendment for Soil and the Environment [Working Title], 2019
Phosphorus (P) eutrophication in the water bodies is of global concern. The role of biochar in the mitigation of (P) eutrophication has recently received substantial attention. Agriculture is the main source of P in the water bodies, as a result of excessive fertilizer and manure application. Excessive P results in excessive primary production in the water bodies, leading to anoxic conditions, growth of toxic algae blooms, altering plant species composition and biomass. Therefore, resulting in food web disruption, fish kill, toxins production and recreation areas degradation. When biochar is applied on farm, it has potential to sorb/adsorb P, immobilizing it, slowing its translocation to the water bodies. However, biochar effectiveness in P sorption is influenced by both feedstock type and pyrolysis temperature. The interaction between feedstock type and pyrolysis temperature influences the biochar pH, surface area, aromatic carbon, cation exchange capacity, surface charge density, biochar internal porosity and polar and nonpolar surface sites that promote nutrient absorption. Hence, biochar properties have a broad spectrum that influences how biochar reacts with P sorption; therefore, it is not appropriate to extrapolate observed results to different materials. Biochar that promote P sorption rather than desorption should be considered and designed to meet specific management practices.
Biochar
Silicate minerals constitute the main components in silicon (Si)-rich biomass, affecting the phosphorus (P) adsorption and release competencies of mineral-engineered biochar; however, the mechanisms underlying their differences remain largely unresolved. To examine these interactions, we investigated the mineralogical compositions and quantified the P-adsorption capacities of Al-, Fe-, Mn-, Zn-, and Mg-engineered biochars from Si-rich rice husk material. The potential uses of P-laden mineral-engineered biochar for P fertilizers were assessed using citric acid extraction. The results from X-ray diffraction, scanning electron microscopy, and Fourier transform infrared spectrometry revealed that mixed metal (oxyhydr)oxides and metal-silicate compounds precipitated in the biochar structure and acted as the main P adsorbents. Micro-crystalline silicates derived from the biomass-induced metal-silicate precipitates in all engineered biochars, which effectively retained the aqueous P with v...
Sorption and desorption of phosphate on biochar and biochar–soil mixtures
The term biochar refers to materials with diverse chemical, physical and physicochemical characteristics that have potential as a soil amendment. The purpose of this study was to investigate the P sorption/desorption properties of various slow biochars and one fast pyrolysis biochar and to determine how a fast pyrolysis biochar influences these properties in a degraded tropical soil. The fast pyrolysis biochar was a mixture of three separate biochars: sawdust, elephant grass and sugar cane leaves. Three other biochars were made by slow pyrolysis from three Amazonian tree species (Lacre, Ing a and Emba uba) at three temperatures of formation (400°C, 500°C, 600°C). Inorganic P was added to develop sorption curves and then desorbed to develop desorption curves for all biochar situations. For the slow pyrolysis, the 600 ºC biochar had a reduced capacity to sorb P (4-10 times less) relative to those biochars formed at 400°C and 500°C. Conversely, biochar from Ing a desorbed the most P. The fast pyrolysis biochar, when mixed with degraded tropical mineral soil, decreased the soil's P sorption capacity by 55% presumably because of the high soluble, inorganic P prevalent in this biochar (909 mg P/kg of biochar). Phosphorus desorption from the fast pyrolysis biochar/soil mixture not only exhibited a common desorption curve but also buffered the soil solution at a value of ca. 0.2 mg/L. This study shows the diversity in P chemistry that can be expected when biochar is a soil amendment and suggests the potential to develop biochars with properties to meet specific objectives.
2019
This report examines several different strategies for creating engineered biochars from waste lignocellulosic materials with enhanced properties chosen specifically for their potential to integrate into urban waste processing biorefineries. Specifically, the goal was to improve capacity for adsorption of phosphates and hydrogen sulfide by chars derived from several lignocellulosic materials including fiber from anaerobically digested dairy manure (AD fiber), urban wood residuals, and wheat straw. The impacts on water holding capacity was also examined as this is an important function for biochar incorporated into soils. In the first generation (CO2-activated) biochar, a pyrolysis step is followed by an activation step with CO2. CO2-activated char from anaerobically digested (AD) fiber had phosphate adsorption capacity of 32.4 mg g-1 biochar. The hydrogen sulfide (H2S) adsorption capacity of AD fiber-derived chars was 51.2 mg g-1. The breakthrough time for adsorption of hydrogen sulfide for AD fiber-derived char produced at 750℃ compared favorably to commercial activated carbon. Second generation biochar was produced using “nitrogen doping” (the process of introducing nitrogen functional groups into a carbonaceous material). When nitrogen-doped char, produced using a single step process had a phosphate adsorption capacity nearly double that of char produced using a two-step process (110.3 mg g-1 vs. 63.1 mg g-1). Our team also conducted analysis of water holding capacity with N-doped biochars produced from urban wood residuals (particle board and compost overs). When raw (non N-doped) char from particle board was blended with Quincy sand soil at a rate of 10% by weight, water holding capacity more than doubled compared to no biochar, from 29.9 to 69.6 % by weight. However, N-doping provided little benefit compared to untreated (raw) biochar, and actually reduced the water holding capacity compared to raw biochar at higher application rates. Third generation biochars were produced by impregnating feedstock with metals (Mg, Ca, or Fe) and then using N-doping process to create a metal-N-doped biochar from both pure cellulose and wheat straw feedstocks. Metal-N doping using Mg and N together were effective at improving phosphate adsorption capacity for cellulose char to 335 mg g-1, and from wheat straw to 288 mg g-1. With further development, these processes hold great promise for integration into a municipal biorefinery. For example, activated biochar derived from AD fiber could be used for H2S removal from AD biogas and phosphate removal from AD effluent. Chars from could be sold and used to adsorb phosphate from a variety of other wastewaters or to reduce H2S emissions from compost. Within either of these scenarios, the resulting phosphate-charged biochar could perhaps be sold as a nutrient-rich soil amendment, though more information is needed to determine nutrient availability to plants following soil amendment with these materials.