Experimental Study on Adsorption of Hexavalent Chromium with Microwave-Assisted Alkali Modified Fly Ash

Coal fly ash, a kind of solid waste generated from coal-fired power stations, can be used as an absorbent for Cr(VI) from aqueous solution. The adsorption characteristics of microwave-assisted alkali modified fly ash to hexavalent chromium had been investigated. Many experimental conditions including pH, contact time, temperature, and fly ash dosage have significant impacts on adsorption performance of modified fly ash. The optimum conditions for the preparation of modified fly ash were as follows: microwave power 600 W, microwave temperature 60 °C, and microwave time 10 min. Batch experiments on adsorption isothermal characteristics of the fly ash modified under the optimal conditions were carried out. The results show that the adsorption of hexavalent chromium ions by modified fly ash is in accordance with the Freundlich and Langmuir isotherm adsorption models, which indicates that the adsorption process is monomolecular adsorption. Environmental-benign utilization of fly ash as low-cost adsorbents in wastewater treatment would bring long-term economic and environmental benefits.     

Combined Removal of Zinc (II) and Cadmium (II) from Aqueous Solutions by Adsorption onto High-Calcium Turkish Fly Ash

The aim of this work is the investigation of possible use of flyash in the removal of zinc (Zn²⁺) and cadmium (Cd²⁺) contained in aqueous solutions. Batch adsorption experiments wereperformed in order to evaluate the removal efficiency oflignite-based fly ash. The parameters studied include contact time, pH,temperature, initial concentration of the adsorbate and fly ashdosage. The contact time necessary to attain equilibrium was found to be two hours. Maximum adsorption occurred in the pH range of 7.0 to 7.5. The percent adsorption of Zn²⁺ and Cd²⁺ increased with an increase in concentration of Zn²⁺ and Cd²⁺, dosage of fly ash and temperature. Theapplicability of Langmuir isotherm suggests the formation ofmonolayer coverage Zn²⁺ and Cd²⁺ ions at the outer surface of the adsorbent. Thermodynamic parameters suggested the endothermic nature of the adsorption process. The fly ashwas found to be an metal adsorbent as effective as activated carbon.     

Effect of Equilibrium Solution Ionic Strength on the Adsorption of Zn,Cu, Cd,Pb, As,and P on Aluminum Mining By-Product

Adsorption onto powdered activated carbon (PAC) is a promising option to remove organic micro-pollutants (OMP) from drinking water sources or wastewater. Since this treatment option requires continuous PAC dosing, sufficient contact time and subsequent separation of the PAC, the integration into existing process chains is challenging. In the present investigation, the pre-loading of a deep bed filter with PAC used as fixed bed adsorber was investigated. The retention and distribution of an exemplary PAC in a pumice rapid filter were determined. Gravimetry combined with combustion of the PAC at 550 °C was applied to differentiate between PAC and filter material residues and revealed comparably high PAC immobilization in the upper third of the pumice filter. Comparative adsorption experiments in batch with suspended PAC and continuous filtration tests with immobilized PAC showed advantageous results for immobilized PAC with regard to the removal of OMP and the sum parameters dissolved organic carbon and UV light absorption at 254 nm wavelength. The results indicate that a conventional rapid filter together with PAC can be effectively utilized as fixed bed adsorption filter.     

活性炭脱除模拟沼气中H2S的动态试验

利用动态试验,以模拟沼气为研究对象,研究了进气中H_2S的浓度、进气流速、吸附剂质量及吸附剂粒径等因素对吸附柱穿透时间及穿透吸附容量的影响。研究结果表明,提高进气中的H_2S浓度和进气流速,增加活性炭的粒径可以有效地缩短穿透时间。当其他试验条件保持不变时,进气中H_2S的体积分数分别为0.0124%和0.0454%时,其对应的穿透容量分别为1.20和1.86 mg/g;进气速度为0.15 L/min时的穿透容量为0.30 L/min时的1.6倍;粒径0.84~2.00 mm时的穿透容量只有0.42~0.84 mm时的58%。因此,提高活性炭对H_2S的穿透吸附容量可以通过提高进气中H_2S的浓度,降低进气速度、减小活性炭的粒径等方法实现。通过Bangham吸附速率方程的模拟可知,未经改性的活性炭对H_2S的吸附行为同样符合Bangham吸附速率方程。该研究可为未改性活性炭沼气脱硫装置的放大和实际应用提供参考。     

Chemical Oxygen Demand (COD) Reduction in Domestic Wastewater by Fly Ash and Brick Kiln Ash

The potential of fly ash, brick kiln ash and commercial activated carbon is determined for the reduction of chemical oxygen demand (COD) from domestic wastewater. Laboratory experiments are conducted for investigating the effect of treatment time, adsorbent dose, pH of the media, initial COD concentration, agitation speed and particle size of adsorbents on the COD reduction from the domestic wastewater. Starting with an initial COD concentration of 1080 mg/l the maximum COD reduction achieved for fly ash was 87.84%, brick kiln ash was 83.22% and commercial activated carbon was 99.35 %. These values were achieved when the wastewater was treated with activated carbon for 180 min, fly ash 250 min and brick kiln ash 300 min and the adsorbent dose was kept respectively at 40 g/l, 60 g/l and 45 g/l for activated carbon, fly ash and brick kiln ash. Agitation speed was kept constant at 600 rpm and the pH was maintained at 2 for activated carbon and fly ash and 5 for brick kiln ash. The maximum percent reduction is for 0.053 mm or smaller size of the particles. Though the adsorption capacity of the ash for reducing the COD is lower than that of the commercial activated carbon, the low material cost can make it an attractive option for the treatment of domestic wastewater.     

Removal of Iron and Manganese from Water with a High Organic Carbon Loading. Part II: The Effect of Various Adsorbents and Nanofiltration Membranes

This paper describes the second part of an investigation into the removal of iron and manganese from water with a high dissolved organic carbon (DOC) loading. This investigation focused on the use of ferrichloride as coagulant in conjunction with hydrogen peroxide as an oxidant and different physical treatment processes, such as adsorption and nanofiltration, to reduce dissolved iron and manganese in water with a high DOC loading. It was found that nanofiltration employing H₂O₂ is the only treatment capable of producing drinking water within the set requirements of the treatment facility. Both fly ash and powdered activated carbon (PAC) used as adsorbents yielded a low percentage removal of DOC, while all the treatment methods evaluated accomplished high removals of the metallic ions Fe(II) and Mn(II). From the results a staggered treatment approach is recommended to obtain the best results at the lowest cost.     

Evaluation of Activated Carbon-Coated Electrode in Electrostatic Precipitator and Its Regeneration for Volatile Organic Compounds Removal

Activated carbon-coated electrode was developed and applied in electrostatic precipitator to remove volatile organic compound gases simultaneously with dust particles from a contaminated air. The activated carbon coating mixture was made up of powdered activated carbon (AC), carbon black (CB), and polyvinyl acetate (PVA), and methanol was added as a solvent to control the thickness of the mixture for best coating performance. During the coating process, the Brunauer-Emmett-Teller (BET) surface decreased to 86% of the original AC while pore volume percentages of macro pore increased, compared to micro- and meso-sized pores. The adsorption isotherm of benzene, toluene, ethyl benzene, and xylene (BTEX) gases onto the original AC and AC coating mixture (AC thoroughly mixed with PVA and methanol for coating and powdered again after dry) were tested and compared to each other, and it was found that both isotherm were best fitted to Freundlich and Langmuir isotherm with the order of adsorption capacities; ethyl benzene?>?m-xylene?>?toluene?>?benzene. The difference between adsorption capacities was clearer with the absorbent AC but became little with the AC coating mixture. In removing BTEX at increasing linear velocities up to 6.7 cm/s, it appeared that the surface area of AC electrode was directly proportional to its removal rate of BTEX. The thermal desorption was applied to regenerate the AC electrode, and 200 °C was found to be most efficient for benzene desorption, but higher temperature would be required for entire BTEX gases desorption.     

Characteristics of synthetic soil aggregates produced by mixing acidic “Kunigami Mahji” soil with coal fly ash and their utilization as a medium for crop growth

Abstract

This study was carried out to examine the characteristics and potential utilization of synthetic soil aggregates (SSA) produced by mixing acidic “Kunigami Mahji” soil in Okinawa, Japan, with waste materials, such as coal fly ash, used paper and starch, as media for crop growth. A series of different SSA were produced by incorporating various percentages (i.e. 0, 20, 40, 60, 80 and 100%) of coal fly ash into the “Kunigami Mahji” soil with used paper and starch. The particle density and bulk density of the original “Kunigami Mahji” soil were 2.67 and 1.23 g cm^?3, respectively. The increased percentages of added coal fly ash, used paper and starch significantly decreased the particle and bulk densities of SSA compared with the original “Kunigami Mahji” soil because of the low particle and bulk densities of the coal fly ash (2.10 and 0.96 g cm^?3, respectively). The SSA particle density varied between 2.39 and 2.14 g cm^?3, and bulk density varied between 0.72 and 0.81 g cm^?3, depending on the additional percentages of coal ash from 20–100%. Maximum water-holding capacity and saturated hydraulic conductivity were increased with the formation of SSA with coal fly ash, used paper and starch binder compared with the original “Kunigami Mahji” soil. The saturated hydraulic conductivity values of the SSA increased because of their low bulk density compared with the original soil. The addition of coal fly ash, used paper and starch to the acidic (pH = 4.62) “Kunigami Mahji” soil to form SSA increased the pH (6.70–9.96), electrical conductivity, exchangeable cation concentration and cation exchange capacity. The addition of coal fly ash up to 60% increased the aggregate strength. The growth and yield of komatsuna and soybean crops with SSA as a crop growth medium was assessed. Both crops showed the highest growth and yield when grown with SSA containing 20% of coal fly ash. Synthetic soil aggregates containing more than 20% of coal fly ash reduced plant growth and yield. Therefore, SSA produced from “Kunigami Mahji” soil with 20% of coal fly ash, used paper and starch can be successfully used as a medium for crop growth.     

炭化秸秆对水体中氨氮和磷的吸附性能及其与粉煤灰和炉渣的对比

采用恒温振荡吸附试验方法,研究了炭化秸秆对水体中氨氮和磷的吸附,并与粉煤灰和炉渣两种物料的吸附性能进行了对比。结果表明,炭化秸秆对氨氮和磷的吸附容量和吸附率小于粉煤灰、但大于炉渣,且3种物料对氨氮和磷的吸附容量,都随着吸附剂投加量的增加而减小;炭化秸秆和粉煤灰的吸附率随着吸附剂投加量的增加而增大,炉渣则减小;炭化秸秆和炉渣对氨氮和磷的吸附率随着pH值的增大而呈现不规则的增大趋势。3种物料对氨氮和磷的吸附容量受pH的影响很小,粉煤灰对氨氮的吸附容量在pH为6时最高,但在pH为4时炭化秸秆对氨氮的吸附容量最低。     

Remediation of Fly Ash Dumpsites Through Bioenergy Crop Plantation and Generation: A Review

Utilization of fly ash, a byproduct of coal combustion in thermal power plants, is a sustainable use of waste for power generation. Discarding fly ash as waste in landfills/ash ponds may not only be regarded as a loss of valuable land and essential nutrients, but also pose a significant health hazard due to fine air-borne particles and leaching of heavy metals. The presence of essential macro- and micronutrients and its porosity make fly ash an excellent soil amendment for plant growth as an organic nitrogen (N) and carbon (C) supplementation. As harmful heavy metals make fly ash unsafe for agronomy, bioenergy crop plantation and energy generation from different thermochemical conversions of the biomass would be an ideal method for coal fly ash utilization through which carbon-neutral fuel can be generated from fossil fuel, thus reducing climate change impact. This review summarizes the development of bioenergy plantation and silviculture at fly ash dumpsites with an integrated phyto-bio-rhizo-mycoremediation approach and assesses utilization of the valuable biomass for thermal energy, electricity, and biofuel generation with inclusion of a SWOT analysis (a strategic technique typically used to help identify the strength, weakness, opportunities, and threat). Bioenergy crop production through integrated phytomanagement can generate billions of dollars of wealth from waste and provides a sustainable solution for fly ash management, with environmental, economic, and social benefits.     

Comparison of Cadmium Ion Adsorption on Various ACTIVATED CARBONS

Studies on the removal of cadmium(II) ions from aqueous solutions by adsorption on various activated carbons [commercial activated carbon (CAC) and chemically prepared activated carbons (CPACs) from raw materials such as straw, saw dust and datesnut] have been carried out with an aim to obtain information on treating effluents containing Cd(II) ions. Factors influencing the adsorption of Cd(II) ions from aqueous solution by ACs have been investigated by following a batch adsorption technique at 30± 1 ^°C. The percentage removal increased with decrease in initial concentration and particle size of CPACs and an increase in contact time, dose and initial pH of the solution. Adsorption process was inhibited by the added electrolytes. The adsorption data were fitted with the Langmuir, Dubinim–Radushkevich and Freundlich isotherms and first-order kinetic equations viz., first-order, Lagergren and Bhattacharya–Venkobachar equations and intra-particle diffusion model. The kinetics of adsorption is first order with intra-particle diffusion as one of the rate determining steps. Thermodynamic parameters were obtained from equilibrium constants measured at 30, 35 and 40 ^°C (Error = ± 1 ^°C). Results of the studies on adsorption of Cd²⁺ ions from simulated wastewater were compared with that of CAC and Tulsion CXO-9(H), a commercial ion exchange resin/cationic resin (CR). Straw carbon showed the maximum adsorption capacity towards Cd²⁺ ions and a high value of rate constant of adsorption. Straw carbon is an alternative low-cost adsorbent to CAC.     

Weathered Fly Ash Does Not Affect Soil And Biosolid Carbon Mineralization

Fly ash and biosolid wastes can be mixed and applied to soil as a means of disposal. A significant decline in soil respiration following waste application indicates restricted activities of functional microbial populations. Weathering decreases salinity and neutralizes alkalinity in fly ash, but there is little information on the effects of unweathered fly ash and biosolid mixtures on soil carbon (C) mineralization. The objective of this study was to determine the effects of a weathered fly ash–limestone scrubber residue (LSR) mixed with an aerobically digested biosolid on soil respiration in a laboratory incubation study. Biosolids significantly increased carbon dioxide (CO₂) production (p < 0.05), but up to 6.75% (w/w) fly ash did not. Mean total C mineralization was 770 mg CO₂‐C kg^?1 soil in the control and 3,810 mg CO₂‐C kg^?1 soil in the 6.75% (w/w) biosolid treatment. Fly ash with neutral pH and low salinity appears unlikely to affect soil and biosolid C mineralization.     

Predominance of Dehalococcoides in the presence of different sulfate concentrations

Urban stormwater runoff is contaminated by nutrients that wash off of roadways, parking lots and lawns during storms. In-ground permeable filter systems that consist of carefully selected filter material have the potential to remove these nutrients from the run-off. In this paper, four filter materials, calcite, zeolite, sand and iron filings, were investigated using laboratory batch tests to evaluate their efficiency in the removal of nitrate and phosphate from the simulated stormwater at different initial concentrations under the same 24-h exposure time period. The range of removal for nitrate was from 39 % to 65 % for calcite, from 42 % to 77 % for zeolite, from 40 % to 70 % for sand, and from 74 % to 100 % for iron filings. The removal of phosphate ranged from 35 % to 41 % for calcite, 59 % to 100 % for zeolite, 49 % to 100 % for sand, and 73 % to 100 % for iron filings. The removal of nitrate is mainly attributed to electrostatic adsorption, except when iron filings were used as a filter material where additional processes such as electrochemical reduction, ligand complexation and precipitation may have contributed to the higher nitrate removal. Phosphate removal is also attributed to electrostatic adsorption in all filter materials; however, at higher phosphate concentrations, the precipitation process may be the dominant process for all of the filter materials except calcite. The Langmuir and Freundlich isotherms fitted the observed nonlinear adsorption results, but the mechanism of removal of phosphate changed from adsorption to precipitation at concentrations higher than 1 mg/l in zeolite, sand, and iron filings; therefore, the adsorption models are valid below this concentration limit. A typical application of these batch adsorption test results is presented in the design of a field in-ground permeable filter system.     

不同基质去除水中氮、磷的作用机理及效应

对粉煤灰、矾土、活性炭、蛭石和火烧石5种基质的元素含量和表面化学性状进行了研究,并比较了这5种基质对P和NH4+-N的吸附性能。结果表明:粉煤灰呈碱性,具有较高的Fe、Ca含量,胶体氧化铁和水溶性Ca含量也最高,矾土呈酸性,Al含量和游离氧化铝含量最高,蛭石和火烧石呈中性,其中蛭石含有21.6%的Mg,活性炭比表面积最大。Langmuir等温吸附曲线方程能够对上述基质的P、NH4+-N吸附过程进行了很好的拟合,其中P理论饱和吸附量由大到小依次为粉煤灰>矾土>火烧石>活性炭>蛭石,NH4+-N饱和吸附量由大到小依次为蛭石>粉煤灰>火烧石>活性炭>矾土。双元素(P和NH4+-N)溶液下,基质对P或NH4+-N的理论饱和吸附量较单元素(P或NH4+-N)溶液下要低。在5种基质中,粉煤灰对P、NH4+-N的综合吸附能力较强,推荐其作为水体N、P污染修复的首选基质。     

Adsorptive Removal of Chromium(VI) from Aqueous Solution by an Agricultural Waste-Based Activated Carbon

Activated carbon was prepared from an agricultural waste, coconut coir, and its characteristics were compared with that of a commercial bituminous coal-based activated carbon. The activated carbon possessed higher surface area, micropore area, micropore volume and average pore diameter, and well-developed meso- and micropores. Batch test on adsorption of chromium(VI) by the coconut coir activated carbon showed that the extent of chromium(VI) adsorption was dependent on chromium(VI) concentration, contact time, pH and activated carbon dose. Maximum adsorption occurred at pH 1.0–2.0 and equilibrium adsorption was attained in 2.5 h. Chromium(VI) adsorption followed pseudo second-order kinetics. Equilibrium chromium(VI) adsorption data for the coconut coir activated carbon and the commercial activated carbon were described by the Langmuir and Freundlich isotherm models and indicated higher chromium(VI) adsorption capacity of the coconut coir activated carbon. Chromium(VI) adsorption capacity of the coconut coir activated carbon was compared with that of activated carbon prepared from different waste material and bituminous coal. The coconut coir activated carbon showed high limiting capacity for adsorption of chromium(VI). Coconut coir activated carbon is a suitable substitute for commercial activated carbon in the adsorptive removal of chromium(VI) from water.     

Removal of Remazol Brilliant Blue Dye from Dye-Contaminated Water by Adsorption Using Red Mud: Equilibrium, Kinetic, and Thermodynamic Studies

Utilization of industrial solid wastes for the treatment of wastewater from another industry could help environmental pollution abatement, in solving both solid waste disposal as well as liquid waste problems. Red mud (RM) is a waste product in the production of alumina and it poses serious pollution hazard. The present paper focuses on the possibility of utilization of RM as an adsorbent for removal of Remazol Brilliant Blue dye (RBB), a reactive dye from dye-contaminated water. Adsorption of RBB, from dye-contaminated water was studied by adsorption on powdered sulfuric acid-treated RM. The effect of initial dye concentration, contact time, initial pH, and adsorbent dosage were studied. Langmuir isotherm model has been found to represent the equilibrium data for RBB?CRM adsorption system better than Freundlich model. The adsorption capacity of RM was found to be 27.8?mg dye/g of adsorbent at 40?°C. Thermodynamic analysis showed that adsorption of RBB on acid-treated RM is an endothermic reaction with ?H ⁰ of 28.38?kJ/mol. The adsorption kinetics is represented by second-order kinetic model and the kinetic constant was estimated to be 0.0105?±?0.005?g/mg?min. Validity of intra-particle diffusion kinetic model suggested that among the mass transfer processes during the dye adsorption process, pore diffusion is the controlling step and not the film diffusion. The process can serve dual purposes of utilization of an industrial solid waste and the treatment of liquid waste.     

Activated Carbon Produced from Waste Wood Pallets: Adsorption of Three Classes of Dyes

Activated carbon was derived from waste wood pallets in Hong Kong via phosphoric acid activation and applied to adsorption of basic dye (methylene blue), acid dyes (acid blue 25 and acid red 151), and reactive dye (reactive red 23). The results showed that respective adjustment in phosphoric acid concentration, impregnation ratio, activation temperature, and activation time could maximize the surface area and pore volume of activated carbon. An increase of impregnation ratio or activation temperature significantly influenced the pore size distribution by expanding the porous structure and creating more macropores than micropores. The characterization of the carbon surface chemistry using Fourier-transform infrared (FTIR) spectroscopy, however, revealed a decrease in the amount of several functional groups with increasing activation temperature. The physical properties (surface area and pore volume) of the wood waste-derived activated carbon (using 36% phosphoric acid with an impregnation ratio of 1.5 at an activation temperature of 550°C for 1.5 h) were comparable to those of commercial activated carbon (Calgon F400). The contrasting pH effects on the adsorption of different classes of dyes signified the importance of both electrostatic interaction and chemical adsorption, which correlated to pH-dependent dissociation of surface functional groups. It is noteworthy that the physical properties of activated carbon were insufficient to account for the observed dye adsorption behavior, whereas the surface chemistry of activated carbon and the nature and chemical structure of dyes were more important. The fast kinetics and high capacity of dye adsorption of wood waste-derived activated carbon suggest that production of activated carbon from different types of wood waste should merit further investigation.     

Defluoridation of water by adsorption on fly ash

The ability of fly ash to remove fluoride from water and wastewaters has been studied at different concentrations, times, temperatures and pH of the solution. The rate constants of adsorption, intraparticle transport, mass transfer coefficients and thermodynamic parameters have been calculated at 30, 40, and 50 °C. The empirical model has been tested at various concentration for the present system. The removal of fluoride is favorable at low concentration, high temperature and acidic pH.

     

A Comparison of Inorganic Solid Wastes as Adsorbents of Heavy Metal Cations in Aqueous Solution and Their Capacity for Desorption and Regeneration

The adsorption capacity of seven inorganic solid wastes [air-cooled blast furnace (BF) slag, water-quenched BF slag, steel furnace slag, coal fly ash, coal bottom ash, water treatment (alum) sludge and seawater-neutralized red mud] for Cd²⁺, Cu²⁺, Pb²⁺, Zn²⁺ and Cr³⁺ was determined at two metal concentrations (10 and 100 mg?L^?1) and three equilibrium pH values (4.0, 6.0 and 8.0) in batch adsorption experiments. All materials had the ability to remove metal cations from aqueous solution (fly and bottom ash were the least effective), their relative abilities were partially pH dependant and adsorption increased greatly with increasing pH. At equimolar concentrations of added metal, the magnitude of sorption at pH 6.0 followed the general order: Cr³⁺????Pb²⁺????Cu²⁺?>?Zn²⁺?=?Cd²⁺. The amounts of previously sorbed Pb and Cd desorbed in 0.01 M NaNO₃ electrolyte were very small, but those removed with 0.01 M HNO₃, and more particularly 0.10 M HNO₃, were substantial. Water treatment sludge was shown to maintain its Pb and Cd adsorption capability (pH 6.0) over eight successive cycles of adsorption/regeneration using 0.10 M HNO₃ as a regenerating agent. By contrast, for BF slag and red mud, there was a very pronounced decline in adsorption of both Pb and Cd after only one regeneration cycle. A comparison of Pb and Cd adsorption isotherms at pH 6.0 for untreated and acid-pre-treated materials confirmed that for water treatment sludge acid pre-treatment had no significant effect, but for BF slag and red mud, adsorption was greatly reduced. This was explained in terms of residual surface alkalinity being the key factor contributing to the high adsorption capability of the latter two materials, and acid pre-treatment results in neutralization of much of this alkalinity. It was concluded that acid is not a suitable regenerating agent for slags and red mud and that further research and development with water treatment sludge as a metal adsorbent are warranted.     

Removal of chrome dye from aqueous solutions by fly ash

The ability of fly ash to remove Omega Chrome Red ME (a chrome dye, mostly used in textile industries) from water has been studied. It has been found that low adsorbate concentration, small particle size of adsorbent, low temperature, and acidic pH of the medium favor the removal of chrome dye from aqueous solutions. The dynamics of adsorbate transport from bulk to the solid phase has been studied at different temperatures in light of the adsorption of dye on the outer surface as well as diffusion within the pores of fly ash. The applicability of Langmuir isotherm suggests the formation of monolayer coverage of dye molecules on the outer interface of adsorbent. The thermodynamics of chrome dye-fly ash system indicates spontaneous and exothermic nature of the process. The pronounced removal of chrome dye in the acidic range may be due to the association of dye anions with the positively charged surface of the adsorbent.