Wastewater treatment using low cost activated carbons derived from agricultural byproducts--a case study

A variety of low cost activated carbons were developed from agricultural waste materials viz., coconut shell, coconut shell fibers and rice husk. The low cost activated carbons were fully characterized and utilized for the remediation of various pollutants viz., chemical oxygen demand (COD), heavy metals, anions, etc., from industrial wastewater. Sorption studies were carried out at different temperatures and particle sizes to study the effect of temperatures and surface areas. The removal of chloride and fluoride increased with rise in temperature while COD and metal ions removal decreased with increase in temperature, thereby, indicating the processes to be endothermic and exothermic, respectively. The kinetics of COD adsorption was also carried out at different temperatures to establish the sorption mechanism and to determine various kinetic parameters. The COD removal was 47-72% by coconut shell fiber carbon (ATFAC), 50-74% by coconut shell carbon (ATSAC) and 45-73% by rice husk carbon (ATRHC). Furthermore, COD removal kinetics by rice husk carbon, coconut shell carbon and coconut fiber carbon at different temperatures was approximately represented by a first order rate law. Results of this fundamental study demonstrate the effectiveness and feasibility of low cost activated carbons. The parameters obtained in this study can be fully utilized to establish fixed bed reactors on large scale to treat the contaminated water.     

Adsorption of nickel(II) from aqueous solution onto activated carbon prepared from almond husk

Activated carbon was prepared from almond husk by activating without (MAC-I) and with (MAC-II) H(2)SO(4) at different temperatures. The ability of the activated carbon to remove nickel(II) ions from aqueous solutions by adsorption has been investigated under several conditions such as pH, carbonisation temperature of husk, initial concentration of metal ions, contact time, and adsorbent concentration. Optimal conditions were pH 5.0, the carbonisation temperature of 700 degrees C, 50 min of contact time and adsorbent concentration of 5 g/l. The results indicate that the effective uptake of Ni(II) ions was obtained by activating the carbon, prepared from almond husk at 700 degrees C, through the addition of H(2)SO(4). The removal of Ni(II) were found to be 97.8% at initial concentration of 25mg/l and the adsorbent concentration of 5 g/l. When the adsorbent concentration was increased up to 40 g/l, the adsorption density decreased from 4.89 to 0.616 mg/g for MAC-II. In the isotherm studies, the experimental adsorption data fitted reasonably well the Langmuir isotherm for both MAC-I and MAC-II.     

Nano filter from sintered rice husk silica membrane

A nano filter showing the Knudsen flow was demonstrated by a modification of a membrane constructed from rice husk silica. The membrane was prepared by pressing and sintering micron sized rice husk silica with 4 nm pores. The membrane showed a permeability of 5.2 x 10(-8) mol m(-1) sec(-1) Pa(-1) for H2 and ratios of gas permeability 2.1 and 3.2 for k(H2)/k(CH4) and k(H2)/k(CO2), respectively. When the membrane was treated by filtration of approximately 100 nm sized rice husk silica particles, the permeability decreased to 4.9 x 10(-8) mol m(-1) sec(-1) Pa(-1) and the ratios increased to 2.2 and 3.4. In the case of the membrane after treatments with the dispersion and chemical deposition of tetraethylorthosilicate (TEOS), the corresponding permeability and ratios of the membrane were 1.8 x 10(-8) mol m(-1) sec(-1) Pa(-1), and 2.9 and 4.5, respectively. From the change of the ratio of gas permeability for the membrane with modifications, it is suggested that approximately 100 nm sized rice husk silica particles pack the large pores among the micron sized rice husk silica particles while the chemical deposition of tetraethylorthosilicate (TEOS) reveals the gas flow through 4 nm pores in the rice husk silica by blocking large pores.     

Removal of mercury(II) from aqueous solutions and chlor-alkali industry effluent by steam activated and sulphurised activated carbons prepared from bagasse pith: kinetics and equilibrium studies

The adsorption of mercury from aqueous solutions and chlor-alkali industry effluent on steam activated and sulphurised steam activated carbons prepared from bagasse pith have been studied comparatively. The uptake of mercury(II) (Hg(II)) was maximum by steam activated carbon in presence of SO(2) and H(2)S (SA-SO(2)-H(2)S-C) followed by steam activated carbon in presence of SO(2) (SA-SO(2)-C), steam activated carbon in presence of H(2)S (SA-H(2)S-C) and steam activated carbon (SA-C) at the same concentration, pH and temperature of the solution. Adsorption experiments demonstrate that the adsorption process corresponds to the pseudo-second-order kinetic model and equilibrium results correspond to the Langmuir adsorption isotherm. Kinetic parameters as a function of initial concentration, for all adsorbents were calculated. Batch studies indicated that the optimum pH range for the adsorption of Hg(II) on sulphurised carbons was between 4 and 9 and for sulphur free carbon was between 6 and 9 at 30 degrees C. The adsorptive behaviour of the activated carbons is explained on the basis of their chemical nature and porous texture. Decrease in ionic strength and increase in temperature of the solution has been found to improve the uptake of Hg(II). Synthetic and chlor-alkali industrial wastewaters were also treated by sulphurised activated carbons to demonstrate their efficiencies in removing Hg(II) from wastewaters. Some feasibility experiments have been carried out with a view to recover the adsorbed Hg(II) and regenerate the spent activated carbons using 0.2M HCl solution. The data obtained point towards viable adsorbents, which are both effective as well as economically attractive for Hg(II) removal from wastewaters.     

Carbons prepared from Spartina alterniflora and its anaerobically digested residue by H3PO4 activation: characterization and adsorption of cadmium from aqueous solutions

Two series of activated carbons were prepared from Spartina alterniflora and from its anaerobically digested residue by H(3)PO(4) activation at various process conditions, and used as adsorbents for the removal of cadmium (II) in aqueous solutions. The surface areas and pore volumes of carbons were derived from adsorption isotherms (N(2) at 77K). The surface chemistry of carbons was investigated by infrared spectroscopy. Comparison study indicated that physicochemical properties of the activated carbons were strongly dependent not only on activation conditions but also on biopolymer contents of precursors. Several isotherm models were investigated and the adsorption isotherm data were best represented by the Langmuir isotherm model, with a maximum monolayer adsorption capacity of 47.85 mg/g at 25 °C. The results showed that the activated carbon produced from S. alterniflora could be employed as a promising adsorbent for removing cadmium (II) from aqueous solutions.     

The adsorption of chromium (VI) from industrial wastewater by acid and base-activated lignocellulosic residues

This study deals with the adsorption of Cr(VI) from synthetic and industrial wastewater, produced by a sewage plant. The activated carbons were prepared from a lignocellulosic raw material by thermal treatment at 450 and 650 degrees C in the presence of acid (AlCl(3), HCl, H(3)PO(4) and H(2)SO(4)) and base (NaOH) agents. To optimize the adsorption of Cr(VI), the chemical modifications caused by each activating agent (related to the capability of Cr(VI) removal), and the optimal experimental conditions of the pH, Cr(VI) concentration, adsorbent dose and residence time, were studied. Thus, treatment with H(3)PO(4) gives rise to carbons with a high surface area and high efficiency for Cr(VI) removal at short equilibrium times. In contrast, the generation of active surface sites by means of NaOH requires longer equilibrium times, the adsorption being less effective than in the former case. The adsorption isotherms obey the Langmuir equation only in the first stages of the reaction but fit the Freundlich equations over the whole range studied, so the heat of adsorption can be easily calculated. The results also show that the activated carbons obtained can be recovered by filtration with an efficiency of 30% in the third cycle.     

Effects of calcination parameters on the silica phase of original and leached rice husk ash

This paper presents a contribution to the study of the effects of calcination parameters, including temperature and time, on the silica phase of original and leached rice husk ash. X-ray diffraction (XRD) analysis reveals the presence of totally crystalline silica in the original rice husk ash prepared at 800 °C. Fortunately, no indication of the presence in crystalline phase is found in the leached rice husk ash due to leaching. However, specific surface area analysis indicates that the high calcination temperature or the long calcination time renders the amorphous silica in the leached rice husk ash less activity. Therefore, the leaching procedure, the low calcination temperature and the short calcination time are proposed in order to prepare more active amorphous silica from the rice husk.     

A sustainable route for the preparation of activated carbon and silica from rice husk ash

An environmentally friendly and economically effective process to produce silica and activated carbon form rice husk ask simultaneously has been developed in this study. An extraction yield of silica of 72-98% was obtained and the particle size was 40-50 nm. The microstructures of the as-obtained silica powders were characterized by X-ray diffraction (XRD) and infrared spectra (IR). The surface area, iodine number and capacitance value of activated carbon could achieve 570 m(2)/g, 1708 mg/g, 180 F/g, respectively. In the whole synthetic procedure, the wastewater and the carbon dioxide were collected and reutilized. The recovery rate of sodium carbonate was achieved 92.25%. The process is inexpensive, sustainable, environmentally friendly and suitable for large-scale production.     

Adsorption of fluoride in aqueous solutions using KMnO4-modified activated carbon derived from steam pyrolysis of rice straw

Fluoride in drinking water above permissible levels is responsible for human and skeletal fluorosis. In this study, activated carbons (AC) prepared by one-step steam pyrolysis of rice straw at 550, 650, 750 degrees C, respectively, were modified by liquid-phase oxidation using HNO3, H2O2 and KMnO4. Characterization of these 12 carbons was made by their surface area, porosity, acidity, basicity, pH(pzc), pH and ability to remove fluoride anion. Based on the data of the latter factor, the RS2/KMnO4 carbon was selected. Along with batch adsorption studies, which involve effect of pH, adsorbate concentration, adsorbent dosage, contact time, temperature, and Co-ions (SO4(2-), Cl-, Br-). The effects of natural organic matter (NOM) were also made to remove the fluoride from natural water. On the basis of kinetic studies, specific rate constants involved in the adsorption process using RS2/KMnO4 carbon was calculated and second-order adsorption kinetics was observed. Equation isotherms such as Langmuir (L), Freundlich (F), Langmuir-Freundlich (LF) and Dubinin-Radushkevich (DR) were successfully used to model the experimental data. From the DR isotherm parameters, it was considered that the uptake of F- by RS2/KMnO4 carbon proceeds by an ion-exchange mechanism (E=10.46 kJ mol(-1)). The thermodynamic parameters of fluoride sorption were calculated and the sorption process was chemical in nature. The ability of RS2/KMnO4 to remove F- from Egyptian crude phosphoric acid (P(2)O(5)=48.42%) was tested and the adsorption capacity of F- in H(3)PO(4) was greater than that in distilled water. This is may be due to fluoride adsorption enhanced at lower pH of crude acid.     

孔结构对煤基活性炭电极材料电化学性能的影响(英文)

以太西无烟煤为前驱体,NaOH为活化剂制备电化学电容器电极材料。采用N2吸附法及电化学测试对活性炭的孔结构和电化学性能进行了表征。在1mol/L(C2H5)4NBF4/碳酸丙烯酯有机电解液体系中,研究了孔结构对活性炭电极材料的电化学性能的影响。结果表明:以NaOH为活化剂可制备出比表面积943mol/L～2479mol/L、比电容57F/g～167F/g的活性炭电极材料。活性炭电极材料的比电容不仅取决比表面积,而且与活性炭的孔径分布有关。孔径为2nm～3nm的中孔的存在可以有效降低电解液的扩散阻力,提高电极材料比表面积的利用率,从而使电容器的电化学性能得到增强。     

Performance of a modified multi-stage bubble column reactor for lead(II) and biological oxygen demand removal from wastewater using activated rice husk

The excessive release of wastewater into the environment is a major concern worldwide. Adsorption is the one of the most effective technique for treatment of wastewater. In this work activated carbon prepared from rice husk has been used as an adsorbent. In the present investigation a three phase modified multi-stage bubble column reactor (MMBCR) has been designed to remove lead and biochemical oxygen demand (BOD) from wastewater by means of its adsorption onto the surface of activated rice husk. The multi-staging has been achieved by hydrodynamically induced continuous bubble generation, breakup and regeneration. Under optimum conditions, maximum lead and BOD reduction achieved using activated rice husk was 77.15% and 19.05%, respectively. Results showed MMBCR offered appreciated potential benefits for lead removal from wastewater and BOD removal, even this extent of removal is encouraging and the MMBCR can be used a pretreatment unit before subjecting the wastewater to biological treatment.     

Adsorption of zinc by activated carbons prepared from solvent extracted olive pulp

Activated carbons have been prepared by a two-step physical activation with steam at different burn-off levels to study the porosity development and its effect in zinc adsorption from aqueous solutions. The main material used was the residual from the extraction with solvent of the kernel-oil [solvent extracted olive pulp (SEOP)]. Olive, apricot and peach stone have been also used as different precursors. The products were characterized by N2 at 77K adsorption, Hg porosimetry and iodine number determination. The influence of surface complexes and pH has been investigated in an attempt to elucidate the adsorption phenomena. The effect of different treatments [demineralization with H2SO4 and oxidation with (NH4)2S2O8] was also evaluated for the adsorption of zinc species.Both basic and acidic carbons, originated from SEOP, show remarkable adsorption ability at solution pH=7. Their adsorption ability mainly depends on the content and nature of functional surface groups, the ash content of the precursors and the pH of the solution. These activated carbons were proved to be efficient adsorbents for the removal of water pollutants and contaminants.     

Crystalline rice husk silica reinforced AA7075 aluminium chips by cold compaction method

Aluminium matrix composite is highly demanded in various industries due to its low density and good mechanical properties as most commonly studied for metal matrix composite. The properties of the composite be improved with the addition of reinforcement significantly such as silicon carbide, aluminium oxide, and boron carbide that can be mixed easily to metal matrix composite. The study of crystalline rice husk silica reinforced AA7075 aluminium chips on mechanical properties were investigated. The rice husk ash was burned at 1200 °C and it was characterized in the crystalline phase by conducting x-ray diffraction test. The mechanical properties of aluminium matrix composite were obtained by microhardness and compression tests. Results of mechanical properties for the addition of rice husk silica up to 7.5 wt.% composition of crystalline rice husk silica showed increase value of microhardness and compression strength which are the highest value of 75.94 HV 0.1 and 443 MPa, respectively compared to another aluminium matrix composite. Hence, based on investigation to crystalline rice husk silica reinforced aluminium, it has good potential to improve the mechanical properties of aluminium matrix composite which were dependent to the composition of crystalline rice husk silica reinforcement in aluminium matrix composite.     

Performance of electrical double layer capacitors with porous carbons derived from rice husk

The porous structure and electrochemical double layer capacitance of porous carbons prepared from rice husks by using alkali hydroxide as activating agents were investigated. Three samples of carbons prepared by NaOH-activation, three samples prepared by KOH-activation and two samples of commercial carbons have been studied. The porosity of the carbons was characterized by nitrogen adsorption isotherms at 77 K and electrochemical constant current cycling method was used to measure the double layer capacitance. The specific capacitance of the carbons is not linearly proportional to the surface area. Additionally, the double layer capacitance strongly depends on the pore structure and the functional groups. A specific capacitance larger than 200 F g⁻¹ was achieved by using the porous carbon prepared with NaOH (activation temperature: 750 °C; activation time: 30 min). All the carbons prepared with rice husk in this study have larger double layer capacitance (125–210 F g⁻¹) than the commercial grade carbons (78–100 F g⁻¹).     

中孔炭的水玻璃模板法制备、结构调控及球形功能化

以廉价水玻璃为原料, 通过控制水解条件, 合成出具有不同尺寸的SiO₂溶胶, 并与间苯二酚-甲醛(RF)溶胶形成均相的凝胶复合物, 经常压干燥、炭化、酸洗, 得到具有可控结构的中孔炭材料。考察了水解温度、水解时间和反应物组成对孔结构的影响, 并通过氮气吸附、扫描电镜和透射电镜对材料的微观结构进行了表征。结果表明: 中孔炭的孔隙反相复制于SiO₂凝胶网络, 其平均孔径随水解时间的延长或水解温度的升高而增大, 并在6~12 nm范围内精细调控, 而其总孔隙率可以通过改变炭、SiO₂前驱体比例调节。对液相复合溶胶通过悬浮聚合法和喷雾干燥法处理, 分别制备出毫米级和微米级的中孔炭球, 进而实现了中孔炭在宏观形貌上的调控。本工作为中孔炭的低成本制备、精细结构调控以及球形功能化提供了重要参考。     

The sorption of lead(II) ions on rice husk ash

Present study deals with the adsorption of Pb(II) from aqueous solution on rice husk ash. Rice husk is a by-product generally obtained from rice mill. Rice husk ash is a solid obtained after burning of rice husk. Batch studies were performed to evaluate the influences of various experimental parameters like pH, initial concentration, adsorbent dosage, contact time and the effect of temperature. Optimum conditions for Pb(II) removal were found to be pH 5, adsorbent dosage 5 g/L of solution and equilibrium time 1h. Adsorption of Pb(II) followed pseudo-second-order kinetics. The effective diffusion coefficient is of the order of 10(-10)m(2)/s. The equilibrium adsorption isotherm was better described by Freuindlich adsorption isotherm model. The adsorption capacity (q(max)) of rice husk ash for Pb(II) ions in terms of monolayer adsorption was 91.74 mg/g. The change of entropy (DeltaS(0)) and enthalpy (Delta H(0)) were estimated at 0.132 kJ/(mol K) and 28.923 kJ/mol respectively. The negative value of Gibbs free energy (Delta G(0)) indicates feasible and spontaneous adsorption of Pb(II) on rice husk ash. The value of the adsorption energy (E), calculated using Dubinin-Radushkevich isotherm, was 9.901 kJ/mol and it indicated that the adsorption process was chemical in nature. Application study was also carried out to find the suitability of the process in waste water treatment operation.     

Activated carbons from sewage sludge and discarded tyres: production and optimization

This is a study about making use of two residual materials such as sludges from a sewage treatment plant and discarded tyres to generate activated carbons and later optimize the production process. H2SO4 and ZnCl2 were used as chemical activating agents. Liquid-phase adsorption tests were made using the produced carbons to retain methylene blue and iodine. The best precursor was sludge activated with ZnCl2. After optimization studies, the best production methodology involved a 1:1 ratio of sludge and ZnCl2, a heating rate of 5 degrees C/min up to 650 degrees C and a residence time of 5 min. The resulting materials adsorbed up to 139.4 mg/g of methylene blue and 1358.5 mg/g of iodine. Nevertheless these carbons may leach Zn while using. To avoid this two treatments were carried out: one consisting of a coating with a polymer and another involving an intensive washing, which was seen to be more efficient.     

Composition and structure of amorphous silica produced from rice husk and straw

We have studied amorphous silica samples prepared by a thermal method and precipitation from rice processing waste: straw and grain shells (husk and peelings). We have determined their true and bulk densities, silica content, and sorbed water vapor content. The porosity of the samples has been evaluated by different techniques: nitrogen desorption (Barrett-Joyner-Halenda method) and adsorption (BET analysis), water vapor adsorption, sorption of organic dyes (methylene blue and brilliant green), and positron annihilation spectroscopy. The effect of the nature of raw materials and processing procedure on the physicochemical properties of amorphous silica is examined.     

The quantitative estimation of silica in rice husk ash by titrimetric method: A case study for uncertainty calculation

Silicon is an essential element found in cereals, fruits, vegetables pasta, rice, etc. Rice husk ash is one of the most silica rich raw materials after complete combustion among the family of agro wastes. For the preparation of pure activated silica rice husk are now widely used as raw material. Rice husk ashes are now used by various industries for different applications due to its important properties. The exact quantity of silica in the rice husk ash is therefore essential to know before further research. Keeping these facts an attempt has been made to determine the silica content by titrimetric method followed by quantification of uncertainty budget in four different variety of rice husk ash. The major sources of uncertainty in the measurement have been identified as contributions from repeatability, standardization of sodium hydroxide, titration, weight of the sample taken, volume measurement by volumetric flask, burette, pipette, weighing balance etc. All major sources of uncertainty have been identified and combined following the EURACHEM guidelines.     

Synthesis and characterization of high-purity silica nanosphere from rice husk

The work reports the synthesis, characterization, and the properties of high-purity silica nanospheres from low-cost rice husk. Primarily, the rice husk was washed with distilled water (DW) and subjected to acid leaching to remove the impurities. The treated rice husk was annealed at different temperatures (620 and 900 degrees C) for varied time periods to achive the desirable silica nanospheres. The annealing temperature and time considerably affected the properties of the synthesized silica nanospheres. The morphology studies confirmed that the size of nanospheres were of approximately 50-60 nm. The photoluminesence studies revealed that the synthesized silica nanospheres showed less structural defects and good optical properties. On the basis of the formation and the characterization of silica nanospheres a possible mechanism was suggested. Inductively coupled plasma mass spectrometry (ICP-MS) analysis confirmed that the synthesized silica nanospheres contained approximately 99.93% purity.