Synthesis and characterization of magnesium oxide nanoparticle-containing biochar composites for efficient phosphorus removal from aqueous solution.

The effective removal and recovery of phosphorus from aquatic environments are highly important for successful eutrophication control and phosphorus recycling. Herein, we prepared biochar containing MgO nanoparticles (MgO-biochar) by fast pyrolysis of MgCl2-impregnated corn stalks, probed its phosphate adsorption performance. Through the fast pyrolysis, the MgCl2 promoted the formation of micropores and mesoporous, and decomposed into MgO nanoparticles with the size smaller than 100 nm. The adsorption experiments showed that the adsorption property increased with the increase of Mg content, and had a strong correlation with the external surface area. And the phosphate adsorption was well described by the Langmuir-Freundlich model (maximum adsorption capacity was determined as 60.95 mg P/g). Kinetic analysis and characterization analysis of MgO-biochar for different adsorption time indicated that phosphate adsorption onto MgO-biochar was mainly controlled by rapid binding to the external surface (about 75% of the equilibrium adsorption amount), and the uptake rate was limited by the slow diffusion of phosphate into the biochar interior (about 25% of the equilibrium adsorption amount). The results suggested that the synthesized MgO-biochar with enough MgO active site dispersed on a higher external surface can be used as a potential adsorbent for phosphate removal and recovery from aqueous solution.

Effects of pyrolysis temperature and addition proportions of corncob on the distribution of products and potential energy recovery during the preparation of sludge activated carbon.

The potential energy recovery during sludge activated carbon (SAC) preparation by co-pyrolysis of sewage sludge and biomass has recently gained significant attention. This study firstly evaluated the distribution of pyrolysis products including SAC, oils and gases during sludge pyrolysis at different temperatures (400 °C-800 °C) and corncob addition proportions (0-50%, w/w). The results demonstrated that with the increase of pyrolysis temperature, yield of SAC declined dramatically, while yields of pyrolysis oils and gases increased. With increasing addition of corncob, the yields of SAC and pyrolysis oils declined slightly, while the yield of gases generally increased. Then, the potential energy recovery during sludge pyrolysis was calculated, and the highest energy recovery value was 10.21 kJ/g achieved at 800 °C and 50% corncob addition. However, higher pyrolysis temperature over 600 °C resulted in lower yield and iodine adsorption capacity of SAC. Therefore, the suitable conditions were suggested to be at 600 °C with 50% corncob addition considering both adsorption performance of SAC and potential energy recovery efficiency.

Synthesis of a stable magnesium-impregnated biochar and its reduction of phosphorus leaching from soil.

Biochar improves soil fertility and promotes long-term terrestrial carbon sequestration. However, biochar seems not to be stable enough due to physical, chemical and biological reactions. In this study, a novel, stable, and magnesium (Mg)-impregnated biochar was prepared from cow dung and applied to decrease P leaching from soil. XPS, FTIR, XRD, SEM and EDS were used to evaluate the effect of modification and phosphorus(P) sorption on the oxidation resistance of biochar. The results showed that the oxidation resistance of the Mg-impregnated biochar was improved by the formation of MgO on its surface. The soil column experiment indicated that the Mg-impregnated -biochar decreased P loss from leaching by 89.25%. In addition, the available P content of the soil surface layer under Mg-impregnated biochar treatment increased by 3.5-fold relative to that under the control treatment. P sorption also enhanced the oxidation resistance of biochar. The relative contents of CO, CO, and COOH on the surface of P-laden biochar was 20.97% and was lower than those on the surface of biochar without P sorption (33.15%). Oxidation resistance was enhanced by the formation of new MgP crystals, which prevented the oxidation of CC, CC, and CH into CO, CO, and COOH, respectively, by acting as a physical barrier between the biochar surface and oxygen. The results of XRD, SEM and EDS provided evidence for the formation of MgP crystals. Overall, results indicated that the Mg-impregnated biochar can reduce P leaching loss from soil and has enhanced stability.

Phosphorus recovery and reuse by pyrolysis: Applications for agriculture and environment.

Phosphorus ore extraction for soil fertilization supports the demand of modern agriculture, but extractable resource limitations, due to scarcity, impose a P reuse and recycling research agenda. Here we propose to integrate biochar production (pyrogenic carbon) with municipal and agricultural waste management systems, to recover and reuse phosphorous that would otherwise be lost from the ecological food web. A meta-analysis and available data on total P in biochar indicated that P-enriched feedstocks include animal manure, human excreta, and plant-biomass collected from P-polluted sites. Phosphorus in biochar could participate in P equilibriums in soils and is expected to supply P. The release, sorption and desorption of P by biochar will codetermine the potential of P replenishment by biochar and P loss from biochar-amended soils. Abiotic and biotic factors are expected to affect sorption/desorption of P between biochar and soil aggregates, and P acquisition by plants. Chemical extraction, using acid or alkaline solutions, is considered as a means for P retrieval from high P biochar, especially for biochar with high heavy metal contents. To bridge the gap between academia and practice, this paper proposes future development for phosphorus acclamation by pyrolysis: 1) identification of high-P bio-waste for pyrolysis; 2) retrieval of P by using biochar as soil amendment or by chemical leaching; 3) biochar modification by inorganic nutrients, P solubilizing microorganisms and other organic matter; and 4) compatible pyrolysis equipment fit to the current waste management context, such as households, and waste water treatment plants.

Fabrication of granular activated carbons derived from spent coffee grounds by entrapment in calcium alginate beads for adsorption of acid orange 7 and methylene blue.

Biomass-based granular activated carbon was successfully prepared by entrapping activated carbon powder derived from spent coffee grounds into calcium-alginate beads (SCG-GAC) for the removal of acid orange 7 (AO7) and methylene blue (MB) from aqueous media. The dye adsorption process is highly pH-dependent and essentially independent of ionic effects. The adsorption kinetics was satisfactorily described by the pore diffusion model, which revealed that pore diffusion was the rate-limiting step during the adsorption process. The equilibrium isotherm and isosteric heat of adsorption indicate that SCG-GAC possesses an energetically heterogeneous surface and operates via endothermic process in nature. The maximum adsorption capacities of SCG-GAC for AO7 (pH 3.0) and MB (pH 11.0) adsorption were found to be 665.9 and 986.8mg/g at 30°C, respectively. Lastly, regeneration tests further confirmed that SCG-GAC has promising potential in its reusability, showing removal efficiency of more than 80% even after seven consecutive cycles.

Fast pyrolysis of microalgae remnants in a fluidized bed reactor for bio-oil and biochar production.

In this study, pyrolysis of microalgal remnants was investigated for recovery of energy and nutrients. Chlorella vulgaris biomass was first solvent-extracted for lipid recovery then the remnants were used as the feedstock for fast pyrolysis experiments using a fluidized bed reactor at 500 °C. Yields of bio-oil, biochar, and gas were 53, 31, and 10 wt.%, respectively. Bio-oil from C. vulgaris remnants was a complex mixture of aromatics and straight-chain hydrocarbons, amides, amines, carboxylic acids, phenols, and other compounds with molecular weights ranging from 70 to 1200 Da. Structure and surface topography of the biochar were analyzed. The high inorganic content (potassium, phosphorous, and nitrogen) of the biochar suggests it may be suitable to provide nutrients for crop production. The bio-oil and biochar represented 57% and 36% of the energy content of the microalgae remnant feedstock, respectively.

Effect of pyrolysis temperature and heating rate on biochar obtained from pyrolysis of safflower seed press cake.

Biochar is carbon-rich product generated from biomass through pyrolysis. In this study, the effects of pyrolysis temperature and heating rate on the yield and physicochemical and morphological properties of biochars obtained from safflower seed press cake were investigated. The results showed that the biochar yield and quality depend principally on the applied temperature where pyrolysis at 600 °C leaves a biochar with higher fixed carbon content (80.70%) and percentage carbon (73.75%), and higher heating value (30.27 MJ kg(-1)) in comparison with the original feedstock (SPC) and low volatile matter content (9.80%). The biochars had low surface areas (1.89-4.23 m(2)/g) and contained predominantly aromatic compounds. The biochar could be used for the production of activated carbon, in fuel applications, and water purification processes.

Combustion and gasification characteristics of chars from raw and torrefied biomass.

Torrefaction is a mild thermal pretreatment (T<300°C) that improves biomass milling and storage properties. The impact of torrefaction on the gasification and oxidation reactivity of chars from torrefied and raw biomass was investigated. Thermogravimetric analysis was used to study the differences in O(2) and steam reactivity, between chars prepared from torrefied and raw willow, under both high- and low-heating-rate conditions. High-heating-rate chars were prepared at 900°C with a residence time of 2s. Low-heating-rate chars were prepared with a heating rate of 33°C/min, a maximum temperature of 850 or 1000°C, and a residence time of 30 min or 1h, respectively, at the maximum temperature. Pretreatment by torrefaction consistently reduced char reactivity. Torrefaction's impact was greatest for high-heating-rate chars, reducing reactivity by a factor of two to three. The effect of torrefaction on a residence time requirements for char burnout and gasification was estimated.

Preparation and characterization of activated carbon produced from rice straw by (NH4)2HPO4 activation.

Effects of different pretreatment protocols in (NH(4))(2)HPO(4) activation of rice straw on porous activated carbon evolution were evaluated. The pore structure, morphology and surface chemistry of obtained activated carbons were investigated by nitrogen adsorption, scanning electron microscopy and Fourier transform infrared spectroscopy. It was found that pretreatment combining impregnation with (NH(4))(2)HPO(4) and preoxidation could significantly affect the physicochemical properties of prepared activated carbons. The apparent surface area and total pore volume as high as 1154 m(2)/g and 0.670 cm(3)/g were obtained respectively, when combined process of impregnation followed by preoxidation at 200°C and activation at 700°C was carried out. Meanwhile, the activated carbon yield and maximum methylene blue adsorption capacity up to 41.14% and 129.5 mg/g were achieved, respectively. The results exhibited that (NH(4))(2)HPO(4) could be an effective activating agent for producing activated carbons from rice straw.

Production of activated carbon by K2CO3 activation treatment of cornstalk lignin and its performance in removing phenol and subsequent bioregeneration.

Activated carbon was produced by fast precarbonization of cornstalk lignin in a fluidized bed followed by K2CO3 activation. The results showed that the product is essentially microporous carbon whose Brunauer-Emmett-Teller surface area and pore volume when the carbon was activated at 800 degrees C were 1410 m2/g and 0.77 mL/g, respectively. The potential usefulness of the resultant carbons for removal of phenol from water and their subsequent bioregeneration capabilities were also investigated. The kinetics study showed that all the carbons exhibited a fast adsorption rate and the carbon activated at 800 degrees C had the largest amount of phenol adsorbed due to its greater specific surface area and pore volume. The adsorption isotherms by applying the Langmuir method showed that the monolayer adsorption capacity of carbon activated at 800 degrees C could reach 110.9 mg/g.

Influences of pyrolysis condition and acid treatment on properties of durian peel-based activated carbon.

Durian peel was used for the synthesis of activated carbon used for adsorption of Basic Green 4 dye. Activated carbon was synthesised under either nitrogen (N(2)) atmospheric or vacuum pyrolysis, followed by carbon dioxide (CO(2)) activation. The synthesised activated carbon then was treated with hydrochloric acid (HCl) solution. The results showed that activated carbon synthesised under vacuum pyrolysis exhibited better properties and adsorption capacities than that under nitrogen atmospheric pyrolysis. The HCl treatment improved properties and adsorption capacities of activated carbons. Pseudo-second-order kinetics well described the adsorption of Basic Green 4.

Preparation of activated carbons from coffee husks utilizing FeCl3 and ZnCl2 as activating agents.

Ferric chloride was used as a new activating agent, to obtain activated carbons (AC) from agro industrial waste (coffee husks). This material was compared with two samples from the same raw material: one of them activated by using the classical activating agent, zinc chloride, and the other, activated with a mixture of the two mentioned activating agents in the same mass proportion. The carbonaceous materials obtained after the activation process showed high specific surface areas (BET), with values higher than 900 m(2)g(-1). It is interesting to observe that the activation with FeCl(3) produces smaller pores compared to the activation with ZnCl(2). An important fact to emphasize in the use of FeCl(3) as activating agent is the activation temperature at 280 degrees C, which is clearly below to the temperature commonly employed for chemical or physical activation, as described in the bibliography. All the studied materials showed different behaviors in the adsorption of methylene blue dye and phenol from aqueous solutions.

Preparation and characterization of activated carbon from waste biomass.

Lignocellulosic materials are good and cheap precursors for the production of activated carbon. In this study, activated carbons were prepared from the pyrolysis of soybean oil cake at 600 and 800 degrees C by chemical activation with K(2)CO(3) and KOH. The influence of temperature and type of chemical reagents on the porosity development was investigated and discussed. K(2)CO(3) was found more effective than KOH as a chemical reagent under identical conditions in terms of both porosity development and yields of the activated carbons. The maximum surface area (1352.86 m(2)g(-1)) was obtained at 800 degrees C with K(2)CO(3) activation which lies in the range of commercial activated carbons. Elemental analyses of the activated carbons indicate insignificant sulphur content for all activated carbons. The ash and sulphur contents of the activated carbons obtained with chemical activation by K(2)CO(3) were lower than those by chemical activation with KOH.

Thermal conversion of elephant grass (Pennisetum purpureum Schum) to bio-gas, bio-oil and charcoal.

Elephant grass is an abundant, fast growing plant with significant potential as a renewable energy source and for conversion to higher calorific value fuels. This work investigates thermal conversion of elephant grass to bio-gas, bio-oil and charcoal under two heating rates of 10 and 50 degrees C/min. The energy required to pyrolyse elephant grass was evaluated using computer aided thermal analysis technique, while composition of the resultant bio-gas and bio-oil products were monitored with gas chromatographic and mass spectroscopic techniques. At 500 degrees C, the bio-gas compounds consisted primarily of CO2 and CO with small amounts of methane and higher hydrocarbon compounds. The heat of combustion of the bio-gas compounds was estimated to be 3.7-7.4 times higher than the heat required to pyrolyse elephant grass under both heating rates, which confirms that the pyrolysis process can be self-maintained. Faster heating rate was found to increase the amount of liquid products by 10%, while charcoal yields remained almost the same at 30%. The bio-oil mainly consisted of organic acids, phthalate esters, benzene compounds and amides. The amount of organic acids and benzene compounds were significantly reduced at 50 degrees C/min, while the yields of phthalate esters and naphthalene compounds increased. The difference in bio-oil composition with increased heating rate is believed to be associated with the reduction of the secondary reactions of pyrolysis, which are more pronounced under lower heating rate.