Production of granular activated carbons from select agricultural by-products and evaluation of their physical,chemical and adsorption properties

Representative samples of soft, low density, group 1 (rice straw, rice hulls, sugarcane bagasse) and hard, high density, group 2 agricultural by-products (pecan shells) were converted into granular activated carbons (GACs). GACs were produced from group 1 and 2 materials by physical activation or from group 2 materials by chemical activation. Carbons were evaluated for their physical (hardness, bulk density), chemical (ash, conductivity, pH), surface (total surface area), and adsorption properties (molasses color removal, sugar decolorization) and compared with two commercial reference carbons. The results show that the type of by-product, binder, and activation method determine the properties of GACs. Regardless of the binder, sugarcane bagasse showed a better potential than rice straw or rice hulls as precursor of GACs with the desirable properties of a sugar decolorizing carbon. Pecan shells produced GACs that were closest to the reference carbons in terms of all the properties investigated.     

Select metal adsorption by activated carbon made from peanut shells

Agricultural by-products, such as peanut shells, contribute large quantities of lignocellulosic waste to the environment each growing season; but few, if any, value-added uses exist for their disposal. The objective of this study was to convert peanut shells to activated carbons for use in adsorption of select metal ions, namely, cadmium (Cd2+), copper (Cu2+), lead (Pb2+), nickel (Ni2+) and zinc (Zn2+). Milled peanut shells were pyrolyzed in an inert atmosphere of nitrogen gas, and then activated with steam at different activation times. Following pyrolysis and activation, the carbons underwent air oxidation. The prepared carbons were evaluated either for adsorption efficiency or adsorption capacity; and these parameters were compared to the same parameters obtained from three commercial carbons, namely, DARCO 12x20, NORIT C GRAN and MINOTAUR. One of the peanut shell-based carbons had metal ion adsorption efficiencies greater than two of the three commercial carbons but somewhat less than but close to Minotaur. This study demonstrates that peanut shells can serve as a source for activated carbons with metal ion-removing potential and may serve as a replacement for coal-based commercial carbons in applications that warrant their use.     

Physical and chemical properties of selected agricultural byproduct-based activated carbons and their ability to adsorb geosmin

The objectives of this study were to evaluate selected physical and chemical properties of agricultural byproduct-based activated carbons made from pecan shells and sugarcane bagasse, and compare those properties to a commercial coal-based activated carbon as well as to compare the adsorption efficiency of these carbons for geosmin. Comparison of the physical and chemical properties of pecan shell- and bagasse-based carbons to the commercial carbon, Calgon Filtrasorb 400, showed that pecan shell carbon, but not the bagasse carbon, compared favorably to Filtrasorb 400, especially in terms of surface area, bulk density, ash and attrition. A carbon dosage study done in a model system showed the amount of geosmin adsorbed to be greater for Filtrasorb 400 and the bagasse-based carbon at low carbon concentrations than for the pecan shell carbons, but geosmin adsorption was similar in all carbons at higher carbon dosages. Application of the Freundlich isotherm model to the adsorption data showed that carbons made by steam activation of pecan shells or sugarcane bagasse had geosmin adsorption characteristics most like those of the commercial carbon. In terms of physical, chemical and adsorptive properties, steam-activated pecan shell carbon most resembled the commercial carbon and has the potential to replace Filtrasorb 400 in applications involving removal of geosmin from aqueous environments.     

Adsorption of volatile organic compounds by pecan shell- and almond shell-based granular activated carbons

The objective of this research was to determine the effectiveness of using pecan and almond shell-based granular activated carbons (GACs) in the adsorption of volatile organic compounds (VOCs) of health concern and known toxic compounds (such as bromo-dichloromethane, benzene, carbon tetrachloride, 1,1,1-trichloromethane, chloroform, and 1,1-dichloromethane) compared to the adsorption efficiency of commercially used carbons (such as Filtrasorb 200, Calgon GRC-20, and Waterlinks 206C AW) in simulated test medium. The pecan shell-based GACs were activated using steam, carbon dioxide or phosphoric acid. An almond shell-based GAC was activated with phosphoric acid. Our results indicated that steam- or carbon dioxide-activated pecan shell carbons were superior in total VOC adsorption to phosphoric acid-activated pecan shell or almond shell carbons, inferring that the method of activation selected for the preparation of activated carbons affected the adsorption of VOCs and hence are factors to be considered in any adsorption process. The steam-activated, pecan shell carbon adsorbed more total VOCs than the other experimental carbons and had an adsorption profile similar to the two coconut shell-based commercial carbons, but had greater adsorption than the coal-based commercial carbon. All the carbons studied adsorbed benzene more effectively than the other organics. Pecan shell, steam-activated and acid-activated GACs showed higher adsorption of 1,1,1-trichloroethane than the other carbons studied. Multivariate analysis was conducted to group experimental carbons and commercial carbons based on their physical, chemical, and adsorptive properties. The results of the analysis conclude that steam-activated and acid-activated pecan shell carbons clustered together with coal-based and coconut shell-based commercial carbons, thus inferring that these experimental carbons could potentially be used as alternative sources for VOC adsorption in an aqueous environment.     

Surface properties of granular activated carbons from agricultural by-products and their effects on raw sugar decolorization

Granular activated carbons (GACs) were produced from sugarcane bagasse combined with one of two binders (corn syrup, coal tar) by physical activation and from pecan shells by physical and chemical activation. GACs were evaluated for their physical (hardness, bulk density), chemical (ash, pH), surface (surface area, pore size distribution, surface chemistry), and adsorption properties (molasses color removal, sugar decolorization) and compared with two commercial reference carbons. Results showed that larger surface area, a well-developed macro- and mesoporosity, and a minimal surface charge were desirable in GACs designed for sugar decolorization. Steam activation of pecan shells carbon was the only by-product-activation combination that produced GAC with all the above three desirable characteristics of a good sugar decolorizer. Chemical activation of pecan shells yielded GACs with high surface area and adequate pore size distribution but with large surface charge. In contrast, sugarcane bagasse-based GACs exhibited low surface areas and unsatisfactory physical/chemical properties.     

Pecan shell-based granular activated carbon for treatment of chemical oxygen demand (COD) in municipal wastewater

The present investigation was undertaken to compare the adsorption efficiency of pecan shell-based granular activated carbon with the adsorption efficiency of the commercial carbon Filtrasorb 200 with respect to uptake of the organic components responsible for the chemical oxygen demand (COD) of municipal wastewater. Adsorption efficiencies for these two sets of carbons (experimental and commercial) were analyzed by the Freundlich adsorption model. The results indicate that steam-activated and acid-activated pecan shell-based carbons had higher adsorption for organic matter measured as COD, than carbon dioxide-activated pecan shell-based carbon or Filtrasorb 200 at all the carbon dosages used during the experiment. The higher adsorption may be related to surface area as the two carbons with the highest surface area also had the highest organic matter adsorption. These results show that granular activated carbons made from agricultural waste (pecan shells) can be used with greater effectiveness for organic matter removal from municipal wastewater than a coal-based commercial carbon.     

Activation Methods of Carbonaceous Materials Obtained from Agricultural Waste

Activated carbons belong to the most widely used adsorbent materials. The utility of these materials mainly depends on their chemical surface and porous structure. The method of activation and the nature of the used precursor greatly influence the pore structure and surface functional groups of the activated carbon. Therefore, the main objective of current investigations is to develop or modify the activation method in an optimal manner using appropriate precursors. This review compiles the results of various studies on the synthesis of activated carbons from agricultural waste. Various activation methods, such as physical, chemical, physicochemical, and microwave activation, are discussed. The effects of carbonization and activation parameters, such as temperature, activating agent, and residence time, toward the properties of the activated carbon are reviewed.     

Activated carbons from flax shive and cotton gin waste as environmental adsorbents for the chlorinated hydrocarbon trichloroethylene

Agricultural by-products represent a considerable quantity of harvested commodity crops. The use of by-products as precursors for the production of widely used adsorbents, such as activated carbons, may impart a value-added component of the overall biomass harvested. Our objective in this paper is to show that flax shive and cotton gin waste can serve as a precursor for activated carbon that can be used for adsorption of trichloroethylene (TCE) from both the liquid and gas phases. Testing was conducted on carbon activated with phosphoric acid or steam. The results show that activated carbon made from flax shive performed better than select commercial activated carbons, especially at higher TCE concentrations. The activation method employed had little effect on TCE adsorption in gas or vapor phase studies but liquid phase studies suggested that steam activation is slightly better than phosphoric acid activation. As expected, the capacity for the activated carbons depended on the fluid phase equilibrium concentration. At a fluid concentration of 2 mg of TCE/L of fluid, the capacity of the steam activated carbon made from flax shive was similar at 64 and 80 mg TCE/g of carbon for the vapor and liquid phases, respectively. Preliminary cost estimates suggest that the production costs of such carbons are $1.50 to $8.90 per kg, depending on activation method and precursor material; steam activation was significantly less expensive than phosphoric acid activation.     

Steam activation of chars produced from oat hulls and corn stover

Oat hulls and corn stover were used to produce chars at approximately 500 degrees C. The carbon concentrations of oat hull char and corn stover chars produced were 72.3 and 68.0 wt.%, respectively. Both activation burn-off and Brunauer-Emmett-Teller (BET) surface area appear to exhibit a linear relationship with respect to activation time of oat hulls. As to corn stover activated carbons, there is no linear relationship between activation time and BET surface area. However, activation burn-off of and activation time appear to relate in a linear manner for the activated carbons produced from corn stover chars. Oat hull is better than corn stover as a raw material for the production of activated carbon.     

Ex situ volatile survey of ground almond and pistachio hulls for emission of spiroketals: Analysis of hull fatty acid composition,water content,and water activity

The spiroketal conophthorin has recently been implicated as an important semiochemical of the navel orangeworm moth (Amyelois transitella), a major insect pest to California tree nuts. Additionally, new evidence demonstrates that fungal spores in the presence of linoleic acid produce conophthorin. Numerous investigations have analyzed the volatile emissions of almonds and pistachios under varying conditions, yet there are few reports of conophthorin as a volatile component. Previous studies by our laboratories have suggested almond hulls may be a source of conophthorin production. Accordingly, the volatile emissions of ex situ almond and pistachio ground hulls were surveyed at several developmental stages. Each ground sample was analyzed at various intervals to determine if conophthorin was produced. The almond and pistachio samples were presumed to have a natural fungal bouquet present. Additionally, the fatty acid composition, water content, and water activity of the hulls were analyzed for each sample. Conophthorin and the structurally similar compound chalcogran were detected from almond hulls and shells, but not from the pistachio samples. The almond and pistachio hulls were investigated for four fatty acid components – palmitic, oleic, linoleic, and linolenic. The fatty acid composition of almond hulls varied greatly throughout the growing season, whereas the composition of pistachio hulls remained relatively constant. Both water content and activity were constant in early stages of almond growth then dropped in the later stages of hull split. Spiroketal emission along with other associated volatiles is discussed. This is the first report of the fatty acid composition, water content, and water activity of developing almond and pistachio hulls.     

Testing of Sulphide Loaded Activated Carbon for Uptake of HgII from Aqueous Solution

Activated carbon was prepared from coconut shells by chemical treatment, which was followed by thermal activation. It was mixed with 0.5 % of a sodium sulfide solution for different time intervals and the sulfide loading was observed maximum after one hour of equilibration. The carbons with and without sulfide treatment were used for uptake of mercuric ions from wastewater and the sulfide‐loaded carbon was found to be more effective. The equilibrium data for mercury adsorption obeyed a Freundlich‐type isotherm. Quantitative desorption of mercury was achieved using alkaline solutions of sodium sulfide.     

Granular activated carbons from broiler manure: physical, chemical and adsorptive properties

Broiler manure produced at large concentrated facilities poses risks to the quality of water and public health. This study utilizes broiler litter and cake as source materials for granular activated carbon production and optimizes conditions for their production. Pelletized manure samples were pyrolyzed at 700 degrees C for 1 h followed by activation in an inert atmosphere under steam at different water flow rates, for a period ranging from 15 to 75 min. Carbon physical and adsorptive properties were dependent on activation time and quantity of steam used as activant, yields varied from 18% to 28%, surface area varied from 253 to 548 m2/g and copper ion adsorption varied from 0.13 to 1.92 mmol Cu2+/g carbon. Best overall performing carbons were steam activated for 45 min at 3 ml/min. Comparative studies with commercial carbons revealed the broiler cake-based carbon as having the highest copper ion efficiency.     

Effect of the concentration of inherent mineral elements on the adsorption capacity of coconut shell-based activated carbons

Coconut shells of West Africa Tall, a local variety of the coconut species Cocos nucifera L., were taken from five different geographical locations in Ghana and examined for the presence and concentration levels of some selected mineral elements using atomic absorption spectrometer. Activated carbons were subsequently made from the shells by the physical method. The iodine adsorption characteristics of the activated carbons measured showed a definite relationship to the concentration levels of potassium and other mineral elements in the precursor shell. Samples with lower total minerals content recorded higher iodine numbers. It was observed that the origin of the shells was related to the concentration levels of the analyzed mineral elements in the shells, which in turn affected the adsorption capacity of the activated carbons. The results of this study have important implications for the sourcing of coconuts whose shells are used in the manufacture of activated carbons.     

Production of activated carbon from bagasse and rice husk by a single-stage chemical activation method at low retention times

The production of activated carbon from bagasse and rice husk by a single-stage chemical activation method in short retention times (30-60min) was examined in this study. The raw materials were subjected to a chemical pretreatment and were fed to the reactor in the form of a paste (75% moisture). Chemicals examined were ZnCl2, NaOH and H3PO4, for temperatures of 600, 700 and 800 degrees C. Of the three chemical reagents under evaluation only ZnCl2 produced activated carbons with high surface areas. BET surface areas for rice husk were up to 750m2/g for 1:1 ZnCl2:rice husk ratio. BET surface areas for bagasse were up to 674m2/g for 0.75:1 ZnCl2:bagasse ratio. Results were compared to regular two-stage physical activation methods.     

Diagnosing the Nutritional Balance of Almond (Prunus sp.) Orchards Using DRIS and DOP Methods

Testing and developing nutrient diagnosis methods, which can result in the optimum production of fruits, is of significance. The nutritional balance and requirements of almond (Prunus sp.) orchards, in the city of Saman (province of Chaharmahal and Bakhtiari, Iran, one of the biggest producers of almond in the country), were investigated using the methods of diagnosis and recommendation integrated system (DRIS) and deviation from optimum percentage (DOP) in a two-year research. Using 36 gardens along the Zayandehrud River in a 60-km distance, soil physical and chemical properties, as well as leaf micro- and macro-nutrient contents were determined. Similar plant samples (leaf + petiole) in terms of age, genotype and rootstock were collected from the unfruitful trees. The most deficient nutrients including S, Cu, Zn and Mn were indicated by the DRIS and DOP methods. However, according to the DRIS method Mg, and according to the DOP method N, K and Mg were determined as the most excessive macronutrients. Interestingly, both methods indicated Mo as the most excessive micronutrient. The balance indexes of different nutrients for different orchards indicated that the nutritional balances of the orchards from the highest to the least deficiency are according to the following order Cu > S > Zn > Mn > Cl > P > Ca > Mg > B > N > K > Fe > Mo. Such results indicate the precisions and some similarities between the two methods. However, the two methods were compared using SAS Proc GLM, Proc REG, and Proc NLIN. The analyses indicated that the two methods were significantly different and the DOP method (significant model) indicated higher correlation with the results. Accordingly, the DOP method may be a more accurate method of estimating almond yield as affected by the concentration of different nutrients. It is possible to determine the deficiency, balance and excessiveness of nutrients in almond orchards using the DRIS and DOP methods, which is of economic and environmental significance, worldwide.

     

Shell cracking strength in almond (Prunus dulcis [Mill.] D.A. Webb.) and its implication in uses as a value-added product

Researchers are currently developing new value-added uses for almond shells, an abundant agricultural by-product. Almond varieties are distinguished by processors as being either hard or soft shelled, but these two broad classes of almond also exhibit varietal diversity in shell morphology and physical characters. By defining more precisely the physical and chemical characteristics of almond shells from different varieties, researchers will better understand which specific shell types are best suited for specific industrial processes. Eight diverse almond accessions were evaluated in two consecutive harvest seasons for nut and kernel weight, kernel percentage and shell cracking strength. Shell bulk density was evaluated in a separate year. Harvest year by almond accession interactions were highly significant (p  0.01) for each of the analyzed variables. Significant (p  0.01) correlations were noted for average nut weight with kernel weight, kernel percentage and shell cracking strength. A significant (p  0.01) negative correlation for shell cracking strength with kernel percentage was noted. In some cases shell cracking strength was independent of the kernel percentage which suggests that either variety compositional differences or shell morphology affect the shell cracking strength. The varietal characterization of almond shell materials will assist in determining the best value-added uses for this abundant agricultural by-product.     

Preparation of activated carbons from cattle-manure compost by zinc chloride activation

Dried cattle-manure compost was pyrolyzed by a one-step process to obtain activated carbon using chemical activation by zinc chloride. The influence of activation parameters such as ZnCl(2) to cattle-manure compost (ZnCl(2)/CMC) ratio, activation temperature and retention time on the final products was investigated. The resultant activated carbons were characterized by nitrogen adsorption-desorption isotherms at 77 K. The results showed that the surface area and pore volume of activated carbons, which were estimated by BET and t-plot methods, were achieved as high as 2170 m(2)/g and 1.70 cm(3)/g in their highest value, respectively. Thermogravimetric analysis (TGA) was carried out to monitor the pyrolysis process of cattle-manure compost (CMC) and ZnCl(2) impregnated one (ZnCl(2)/CMC). The capabilities of phenol adsorption were also examined for the CMC carbons prepared with various treatments.     

Influence of preparation conditions in the textural and chemical properties of activated carbons from a novel biomass precursor: the coffee endocarp

In this work a novel biomass precursor for the production of activated carbons (AC) was studied. The lignocellulosic material used as precursor is the coffee bean endocarp, which constitutes an industrial residue from the Portuguese coffee industry. Activation by carbon dioxide and potassium hydroxide produces activated carbons with small external areas and pore volumes up to 0.22 and 0.43cm3g(-1), respectively, for CO2 and KOH activation. All the AC's produced are very basic in nature with point of zero charge higher than 8. SEM/EDX studies indicate the presence of K, O, Ca and Si. By FTIR it was possible to identify the formation on the AC's surface of several functional groups, namely phenol, alcohol, quinone, lactone, pyrone and ether as well as SiH groups. The tailoring of the porous and chemical structure of the activated carbons produced is possible by selecting the appropriate production conditions.     

5-Aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside-induced AMP-activated protein kinase phosphorylation inhibits basal and insulin-stimulated glucose uptake, lipid synthesis, and fatty acid oxidation in isolated rat adipocytes

The objective of this study was to investigate the effects of 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside (AICAR)-induced AMP-activated protein kinase (AMPK) activation on basal and insulin-stimulated glucose and fatty acid metabolism in isolated rat adipocytes. AICAR-induced AMPK activation profoundly inhibited basal and insulin-stimulated glucose uptake, lipogenesis, glucose oxidation, and lactate production in fat cells. We also describe the novel findings that AICAR-induced AMPK phosphorylation significantly reduced palmitate (32%) and oleate uptake (41%), which was followed by a 50% reduction in palmitate oxidation despite a marked increase in AMPK and acetyl-CoA carboxylase phosphorylation. Compound C, a selective inhibitor of AMPK, not only completely prevented the inhibitory effect of AICAR on palmitate oxidation but actually caused a 2.2-fold increase in this variable. Compound C also significantly increased palmitate oxidation in the presence of inhibitory concentrations of malonyl-CoA and etomoxir indicating an increase in CPT1 activity. In contrast to skeletal muscle in which AMPK stimulates fatty acid oxidation to provide ATP as a fuel, we propose that AMPK activation inhibits lipogenesis and fatty acid oxidation in adipocytes. Inhibition of lipogenesis would conserve ATP under conditions of cellular stress, although suppression of intra-adipocyte oxidation would spare fatty acids for exportation to other tissues where their utilization is crucial for energy production. Additionally, the stimulatory effect of compound C on long chain fatty acid oxidation provides a novel pharmacological approach to promote energy dissipation in adipocytes, which may be of therapeutic importance for obesity and type II diabetes.     

Characterization of mesoporous activated carbons prepared by pyrolysis of sewage sludge with pyrolusite

Activated carbons were prepared from sewage sludge by chemical activation. Pyrolusite was added as a catalyst during activation and carbonization. The influence of the mineral addition on the properties of the activated carbons produced was evaluated. The results show that activated carbons from pyrolusite-supplemented sewage sludge had up to a 75% higher BET surface area and up to a 66% increase in mesoporosity over ordinary sludge-based activated carbons. Batch adsorption experiments applying the prepared adsorbents to synthetic dye wastewater treatment yielded adsorption data well fitted to the Langmuir isotherm. The adsorbents from pyrolusite-supplemented sludges performed better in dye removal than those without mineral addition, with the carbon from pyrolusite-augmented sludge T2 presenting a significant increase in maximum adsorption capacity of 50 mg/g. The properties of the adsorbents were improved during pyrolusite-catalyzed pyrolysis via enhancement of mesopore production, thus the mesopore channels may provide fast mass transfer for large molecules like dyes.