Freundlich adsorption isotherms of agricultural by-product-based powdered activated carbons in a geosmin-water system

The present study was designed to model the adsorption of geosmin from water under laboratory conditions using the Freundlich isotherm model. This model was used to compare the efficiency of sugarcane bagasse and pecan shell-based powdered activated carbon to the efficiency of a coal-based commercial activated carbon (Calgon Filtrasorb 400). When data were generated from Freundlich isotherms, Calgon Filtrasorb 400 had greater geosmin adsorption at all geosmin concentrations studied than the laboratory produced steam-activated pecan shell carbon, steam-activated bagasse carbon, and the CO2-activated pecan shell carbon. At geosmin concentrations < 0.07 microg/l for the phosphoric acid-activated pecan shell carbon and below 0.08 microg/l for a commercially produced steam-activated pecan shell carbon obtained from Scientific Carbons, these two carbons had a higher calculated geosmin adsorption than Filtrasorb 400. While the commercial carbon was more efficient than some laboratory prepared carbons at most geosmin concentrations, the results indicate that when the amount of geosmin was below the threshold level of human taste (about 0.10 microg/l), the phosphoric acid-activated pecan shell carbon and the Scientific Carbons sample were more efficient than Filtrasorb 400 at geosmin removal.     

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.     

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.     

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.     

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.     

Removal of color from biomethanated distillery spentwash by treatment with activated carbons

This work examined 19 carbon samples prepared by acid and thermal activation of various agro-residues viz. bagasse, bagasse flyash, sawdust, wood ash and rice husk ash for color removal from biomethanated distillery effluent. Phosphoric acid carbonized bagasse B (PH) showed the maximum color removal (50%). However, commercial activated carbons AC (ME) and AC (LB) showed better performance of over 80% color removal. Besides color removal, activated carbon treatment also showed reduction in chemical oxygen demand (COD), total organic carbon (TOC), phenol and total Kjeldahl nitrogen (TKN). The performance was related to the characteristics of the investigated samples. Further, adsorption isotherms for melanoidins, which is the primary coloring compound in distillery spentwash, followed the Langmuir isotherm implying monolayer adsorption.     

Decolorization of sugar syrups using commercial and sugar beet pulp based activated carbons

Sugar syrup decolorization was studied using two commercial and eight beet pulp based activated carbons. In an attempt to relate decolorizing performances to other characteristics, surface areas, pore volumes, bulk densities and ash contents of the carbons in the powdered form; pH and electrical conductivities of their suspensions and their color adsorption properties from iodine and molasses solution were determined. The color removal capabilities of all carbons were measured at 1/100 (w/w) dosage, and isotherms were determined on better samples. The two commercial activated carbons showed different decolorization efficiencies; which could be related to their physical and chemical properties. The decolorization efficiency of beet pulp carbon prepared at 750 degrees C and activated for 5h using CO2 was much better than the others and close to the better one of the commercial activated carbons used. It is evident that beet pulp is an inexpensive potential precursor for activated carbons for use in sugar refining.     

Acid-activated carbons from almond shells: physical,chemical and adsorptive properties and estimated cost of production

A series of phosphoric-acid activated carbons were made from almond shells using six different activation or activation/oxidation methods. The carbons were compared to each other and to two commercial carbons in an effort to ascertain the relative value of the carbons in terms of yield, surface area, attrition, surface functional groups, organic uptake, metal uptake, as well as estimated cost of production. Of the six methods investigated, the method that produced the best overall performing almond shell carbon and least expensive carbon in terms of production cost was the “Air-Activation” method. This method involved the simultaneous activation and oxidation of almond shells under an air atmosphere.     

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.     

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.     

Physicochemical properties of carbons prepared from pecan shell by phosphoric acid activation

Activated carbons were prepared from pecan shell by phosphoric acid activation. The pore structure and acidic surface groups of these carbons were characterized by nitrogen adsorption, Boehm titration and transmittance Fourier infrared spectroscopy (FTIR) techniques. The characterization results demonstrated that the development of pore structure was apparent at temperatures 250 degrees C, and reached 1130m(2)/g and 0.34cm(3)/g, respectively, at 500 degrees C. Impregnation ratio and soaking time at activation temperature also affected the pore development and pore size distribution of final carbon products. At an impregnation ratio of 1.5, activated carbon with BET surface area and micropore volume as high as 861m(2)/g and 0.289cm(3)/g was obtained at 400 degrees C. Microporous activated carbons were obtained in this study. Low impregnation ratio (less than 1.5) and activation temperature (less than 300 degrees C) are favorable to the formation of acidic surface functional groups, which consist of temperature-sensitive (unstable at high temperature) and temperature-insensitive (stable at high temperature) two parts. The disappearance of temperature-sensitive groups was significant at temperature 300 degrees C; while the temperature-insensitive groups are stable even at 500 degrees C. FTIR results showed that the temperature-insensitive part was mostly phosphorus-containing groups as well as some carbonyl-containing groups, while carbonyl-containing groups were the main contributor of temperature-sensitive part.     

Pyrolysis of plant, animal and human waste: physical and chemical characterization of the pyrolytic products

Pyrolysis (carbonization) has been proposed as one of several optional technologies for disposing and recycling waste products in Japan. Plant wastes (sugarcane bagasse and rice husks), animal waste (cow biosolids) and human waste (treated municipal sludge) were pyrolyzed at temperatures from 250–800 °C in closed containers. The carbonized materials were evaluated for specific physical properties (yield, surface area, density) and specific chemical properties (total carbon, total nitrogen, pH, fixed carbon, ash content, volatility) in order to compare differences in properties among the four waste products. The results indicated that (1) surface area, total carbon, ash content and pH increased as the carbonization temperature increased, while carbonization yield decreased with increasing temperature, (2) product density however was not affected by temperature and (3) correlation coefficients were determined among the physical and chemical properties and several significant correlations were observed. The data indicate that source material had considerable influence on the physical and chemical properties of the carbonized products.     

Study on the removal of pesticide in agricultural run off by granular activated carbon

In this batch study, the adsorption of malathion by using granular activated carbon with different parameters due to the particle size, dosage of carbons, as well as the initial concentration of malathion was investigated. Batch tests were carried out to determine the potential and the effectiveness of granular activated carbon (GAC) in removal of pesticide in agricultural run off. The granular activated carbon; coconut shell and palm shells were used and analyzed as the adsorbent material. The Langmuir and Freundlich adsorption isotherms models were applied to describe the characteristics of adsorption behavior. Equilibrium data fitted well with the Langmuir model and Freundlich model with maximum adsorption capacity of 909.1 mg/g. The results indicate that the GAC could be used to effectively adsorb pesticide (malathion) from agricultural runoff.     

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.     

Purification of sugar beet vinasse - adsorption of polyphenolic and dark colored compounds on different commercial activated carbons

The adsorption on activated carbons of dark colored compounds contained in sugar beet vinasse was studied. Four commercial activated carbons with different properties (particle size, residual acidity and microporous properties) were respectively checked for efficiency at two temperature levels (25 °C and 40 °C) and at four pH levels (2, 3.5, 7, 10). The adsorption of organic molecules was determined by quantifying the amounts of total polyphenolic compounds and total organic carbon. The results showed that the adsorption capacity of dark colored compounds was enhanced by the decrease in both temperature and pH values of the solution. In this study, it is shown that this capacity depends on activated carbon characteristics which can be classified in the following order: particle size > residual acidity > microporous volume. Three models (Langmuir, Freundlich and Dubinin–Radushkevich) were tested from experimental data and compared. The Langmuir model provided the best correlation on all the activated carbons studied.     

Enhanced adsorption of phenolic compounds, commonly encountered in olive mill wastewaters, on olive husk derived activated carbons

Olive husk was used for the preparation of activated carbon by chemical activation with KOH. The effects of carbonization and activation time on carbon properties were evaluated. The surface area of the produced carbons was measured by means of N(2) adsorption at 77K. The carbons with the highest surface area were further characterized by means of elemental analysis, particle size measurement, Boehm titration, zeta potential measurement, and temperature programmed desorption (TPD). Subsequently they were used for adsorption of a mixture of polyphenols consisting of caffeic acid, vanillin, vanillic acid, pi-hydroxybenzoic acid and gallic acid at two temperatures, and their adsorptive capacity was compared to a commercial carbon Acticarbon CX and found to be higher enough. The role of the porosity and surface groups are discussed in relation to the adsorption forces and the properties of the adsorbed substances. A thermodynamic interpretation of the results is also attempted.     

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.     

Performances of toluene removal by activated carbon derived from durian shell

In the effort to find alternative low cost adsorbent for volatile organic vapors has prompted this research in assessing the effectiveness of activated carbon produced from durian shell in removing toluene vapors. Durian shells were impregnated with different concentrations of H₃PO₄ followed by carbonization at 500 °C for 20 min under nitrogen atmosphere. The prepared durian shell activated carbon (DSAC) was characterized for its physical and chemical properties. The removal efficiency of toluene by DSAC was performed using different toluene concentrations. Results showed that the highest BET surface area of the produced DSAC was 1404 m²/g. Highest removal efficiency of toluene vapors was achieved by using DSAC impregnated with 30% of acid concentration heated at 500 °C for 20 min heating duration. However, there is insignificant difference between removal efficiency of toluene by DSAC and different toluene concentrations. The toluene adsorption by DSAC was better fitted into Freundlich model.     

Adsorption of heavy metal ion from aqueous single metal solution by chemically modified sugarcane bagasse

This work describes the preparation of new chelating materials derived from sugarcane bagasse for adsorption of heavy metal ions in aqueous solution. The first part of this report deals with the chemical modification of sugarcane bagasse with succinic anhydride. The carboxylic acid functions introduced into the material were used to anchor polyamines, which resulted in two yet unpublished modified sugarcane bagasse materials. The obtained materials were characterized by elemental analysis and infrared spectroscopy (IR). The second part of this reports features the comparative evaluation of the adsorption capacity of the modified sugarcane bagasse materials for Cu(2+), Cd(2+), and Pb(2+) ions in aqueous single metal solution by classical titration. Adsorption isotherms were studied by the Freundlich and Langmuir models.     

Lignin--from natural adsorbent to activated carbon: a review

The present review compiles the work done over the last few decades on the use of lignin and lignin-based chars and activated carbons as adsorbents for the removal of substances from water and focuses on the utilisation of lignin as adsorbent, its conversion to chars and activated carbons and the use of these materials as adsorbents. Moreover, the review also examines the textural and surface chemical properties of lignin-based activated carbons. The work so far carried out indicates that lignin is relatively non-reactive and probably the component of lignocellulosic precursors primarily responsible for the microporosity of activated carbons. Under appropriate conditions of activation it is possible to obtain materials with surface areas and pore volumes approaching 2000 m(2)g(-1) and 1cm(3)g(-1), respectively, and these materials have capacities for the aqueous phase adsorption of metallic pollutants that are comparable to those of commercial activated carbons. Relatively little work has so far been published and there is considerable scope for more detailed studies on the preparation, characterisation and adsorption applications of lignin-based activated carbons.