Adsorption of organic compounds onto activated carbon

Adsorption isotherms of acetone, propionaldehyde, methylisobutylketone and sucrose from aqueous solutions onto granular activated carbon have been determined.Multi-solute data have been compared with the theoretical prediction obtained from ideal adsorbed solution model.The agreement between calculated and observed results is satisfactory. Only the system sucrosemethylisobutylketone shows significant deviation between experimental and predicted values. Therefore the model can be successfully utilized in design of activated carbon units.     

粉末活性炭吸附对超滤膜污染的影响研究

进行了粉末活性炭(PAC)吸附缓解浸没式和内压式超滤膜污染试验研究,并探讨了PAC吸附缓解膜污染的机理。浸没式超滤膜试验结果表明:PAC通过吸附溶解小分子有机物,减少了膜孔堵塞和膜孔内吸附污染,缓解了运行初期通量的快速下降;但PAC在膜表面的累积会降低浸没式超滤膜的起始通量。内压式超滤膜试验结果表明:膜前PAC吸附预处理能提高对有机物的去除效能,降低膜表面的污染负荷,从而降低TMP及其增长速度。     

Modeling equilibrium adsorption of organic micropollutants onto activated carbon

Solute hydrophobicity, polarizability, aromaticity and the presence of H-bond donor/acceptor groups have been identified as important solute properties that affect the adsorption on activated carbon. However, the adsorption mechanisms related to these properties occur in parallel, and their respective dominance depends on the solute properties as well as carbon characteristics. In this paper, a model based on multivariate linear regression is described that was developed to predict equilibrium carbon loading on a specific activated carbon (F400) for solutes reflecting a wide range of solute properties. In order to improve prediction accuracy, groups (bins) of solutes with similar solute properties were defined and solute removals were predicted for each bin separately. With these individual linear models, coefficients of determination (R²) values ranging from 0.61 to 0.84 were obtained. With the mechanistic approach used in developing this predictive model, a strong relation with adsorption mechanisms is established, improving the interpretation and, ultimately, acceptance of the model.     

The adsorption of heavy metals onto hydrous activated carbon

The absorption characteristics of some heavy metals, namely CU(II), Pb(II), Ni(II) and Zn(II) onto the hydrous activated carbon surface are studied. Carbon type, pH and surface loading are the most important factors affecting the extent of metal removal. The adsorption reaction can be best described by a surface complex formation model. The free metal ions, M²⁺, and their hydroxo species, M(OH)_y^2−y all participate in the absorption reaction. Specific chemical bonding, probably hydrogen bonding provided the sole energy needed for adsorption reaction.     

Natural organic matter (NOM) and pesticides removal using a combination of ion exchange resin and powdered activated carbon (PAC)

The combination of anion exchange resins (AERs) and powdered activated carbon (PAC) was studied to remove both natural organic matter (NOM) and pesticides. Experiments were conducted with high dissolved organic carbon (DOC) surface water (about 6.0mg DOC/L) spiked with both atrazine and isoproturon. AERs, like MIEX and IRA938, showed up to 75% removal of DOC after 30min contact time. The addition of PAC after treatment with these AERs only slightly decreased the residual DOC from 1.4 to 1.2mg/L. Experiments conducted with high (200microg/L) and low (1microg/L) initial pesticide concentrations showed that simultaneous and successive combinations of AER and PAC significantly improve the removal of both pesticides compared with PAC treatment on raw water. The improvement of short-term adsorption kinetics was explained by the adsorption of pesticides on AERs (about 5%) and the removal of high molecular weight (MW) NOM structures by AERs that reduce pore blockage phenomena. For 24h contact time with PAC (adsorption isotherms), the benefit of AER treatment was lower, which indicates that the refractory DOC to AER treatment still competes through direct site competition mechanism. MIEX resin had a distinct behavior since the simultaneous treatment with PAC showed no benefit on pesticide adsorption. The presence of fine residues of MIEX was shown to interfere with PAC adsorption.     

Comparison of natural organic matter adsorption capacities of super-powdered activated carbon and powdered activated Carbon

We examined the natural organic matter (NOM) adsorption characteristics of super-powdered activated carbon (S-PAC) produced by pulverizing commercially available, normal PAC to a submicron particle size range. The adsorption capacities of S-PAC for NOM and polystyrene sulfonates (PSS) with molecular weights (MWs) of 1.1, 1.8, and 4.6 kDa, which we used as model compounds, were considerably higher than those of PAC. The adsorption capacity increases were observed for all five types of carbon tested (two wood-based, two coconut-based, and one coal-based carbon). The adsorption capacities of S-PAC and PAC for polyethylene glycols (PEGs) with MWs of 0.3 and 1.0 were the same. The adsorption capacities of S-PAC for PEGs with MWs of 3.0 and 8.0 kDa were slightly higher than the adsorption capacities of PAC, but the difference in adsorption capacity was not as large as that observed for NOM and the PSSs, even though the MW ranges of the adsorbates were similar. We concluded that the adsorption capacity differences between S-PAC and PAC observed for NOM and PSSs were due to the difference in particle size between the two carbons, rather than to differences in internal pore size or structure, to differences in activation, or to non-attainment of equilibrium that resulted from the change in particle size. The difference in adsorption capacity between S-PAC and PAC was larger for NOM with a high specific UV absorbance (SUVA) value than for low-SUVA NOM. The larger adsorption capacities of S-PAC compared with PAC were explained by the larger specific external surface area per unit mass. We hypothesize that a larger fraction of the internal pore volume is accessible with carbon of smaller particle size because the NOM and PSS molecules preferentially adsorb near the outer surface of the particle and therefore do not completely penetrate the adsorbent particle.     

Removal of aromatic compounds from water on biologically activated carbon

We have carried out an assessment of the content of aromatic compounds (o-nitrophenol, o-aminobenzoic acid) in grains of activated carbon of a biofilter at the stage of stationary water treatment. It was found that the removal degree of aromatic compounds by the biofilm of biologically activated carbon in great measure is determined by the value of the decreasing of Gibbs free energy of adsorption (−ΔG _a ). It is shown that due to the competing action of the biofilm part of the accessible surface of activated carbon is not used for adsorption of organic matter.     

Thermal regeneration of powdered activated carbon (pac) and pac-biological sludge mixtures

A temperature-programmed graphite microfurnace apparatus with mechanical stirring is described for the thermal regeneration of powdered activated carbon (PAC) alone or PAC-biological sludge mixtures from the PAC enhancement of the activated sludge process. Three PACs with widely differing BET areas were evaluated to determine the effects of regeneration on their physical and chemical properties. PAC weight % recoveries were in the range of 60–80%, and the recovery of wastewater (filtered mixed liquor) adsorption capacity regularly exceeded 100% for all carbons. In one case, 222% recovery was achieved. Regeneration always reduced BET area but the effects on I₂ number, pore size distribution and particle size were mixed.Compared to the regeneration of PAC alone, the presence of 40–50% biological sludge was clearly detrimental to the regeneration process. Nevertheless, essentially complete regeneration could be achieved with biomass present by adding a 20-min 400°C, N₂-purge-gas charring step to the usual 20-min, 825°C, H₂O-N₂-CO₂ purge-gas reactivation step. Unfortunately, charring the biomass produced a regenerated material containing 27–34% inerts including carbonaceous char and mineral ash. This black inert material was quite insoluble in dilute HCl and had no useful adsorption capacity. The controlled application of H₂O or trace amounts of O₂ during charring is suggested for the minimization of detrimental char but further research is needed.     

External mass transfer during the adsorption of various pollutants onto activated carbon

A wide range of experimental studies are reported for the adsorption of phenol and p-chlorophenol onto activated carbon—Type Filtrasorb 400—in an agitated batch adsorber. A model has been used to determine the external mass transfer coefficient for the systems and the effect of several experimental variables have been investigated: these include agitation, initial pollutant concentration, carbon mass, carbon particle size and solution temperature. The mass transfer coefficient has been correlated in terms of the dimensionless Sh/Sc^0.33 against each variable. The Sherwood number, Sh = k_fR/D_mol, relates the external mass transfer coefficient k_f to particle radius, R, and molecular diffusivity, D_mol. The Schmidt number, Sc, is the ratio of kinematic viscosity, v, to molecular diffusivity. A few results are also reported for the adsorption of sodium dodecyl sulphate and mercuric ions onto activated carbon.     

粉末活性炭对马拉硫磷的吸附性能研究

以马拉硫磷作为突发性污染物,考察了粉末活性炭对其的吸附效果。试验结果表明,粉末活性炭对纯水和滤后水中的马拉硫磷均具有较好的去除效果,对前者的去除效果更为明显,去除率随活性炭投加量的增加而升高。当马拉硫磷浓度为1.25 mg/L,纯水、滤后水中的活性炭投加量分别为12.0和20 mg/L时,反应120 min后马拉硫磷剩余浓度均低于0.25 mg/L。对滤后水而言,药剂费用约为0.06～0.08元/m3。     

Single and competitive adsorption of Cd and Zn onto a granular activated carbon

Single and competitive adsorption of cadmium and zinc onto granular activated carbon DARCO 12–20 mesh has been investigated. This activated carbon has been shown as an effective adsorbent for both metals. Cadmium and zinc removals increased with pH and decreased with molar metal/carbon ratio. Surface precipitation phenomena have been detected for the higher pHs and molar ratios. The adsorption process has been modelled on the surface complexation Triple Layer Model (TLM). For this purpose, the amphoteric nature of the activated carbon has been studied. Single metal adsorption data have been used to calibrate TLM parameters. A dependence of the adsorption constants on pH and molar metal/carbon ratio has been observed, and a correlation for log K_ads has been determined. In the competitive system, the removal efficiency of the activated carbon decreased for both metals. The TLM model, using surface complexation constants determined from single adsorption experiments, successfully predicted cadmium and zinc removal from the two metal solutions.     

The application of powdered activated carbon for MIB and geosmin removal: predicting PAC doses in four raw waters

Blooms of blue-green algae in reservoirs often produce the musty-earthy taste and odour algal metabolites 2-methylisoborneol (MIB) and geosmin. MIB and geosmin are not removed by conventional water treatment and their presence in the distribution system, even at low ng L-1 levels, can result in consumer complaints. Powdered activated carbon (PAC) can effectively remove MIB and geosmin when the correct dose is applied. The homogeneous surface diffusion model (HSDM) was used to predict PAC doses required to reduce MIB and geosmin concentrations to below 10 ng L-1 at four water treatment plants in Adelaide, South Australia. In jar tests, undertaken under treatment plant conditions, the predicted doses were found to produce water of the desired quality in three of the four waters. The poor predictions found in the fourth water, which had a considerably higher turbidity, were attributed to the incorporation of PAC in a larger, denser floc, leading to a reduced effective contact time of the adsorbent. It was found that higher doses of PAC were required for both compounds to produce acceptable quality water when turbidities rose above 26 NTU.     

Effect of natural organic matter on powdered activated carbon adsorption of trace contaminants: characteristics and mechanism of competitive adsorption

Batch adsorption experiments using powdered activated carbon (PAC) to remove trace synthetic organic chemicals (SOCs) from water containing natural organic matter (NOM) were conducted. The percentage of SOC removed at any contact time and at any PAC dose was observed to be independent of the initial SOC concentration. Equations derived from the ideal adsorbed solution theory and the pore surface diffusion model validated this observation. For the strongly adsorbing SOCs (simazine and simetryn), the percentage of SOC removed was independent only at low initial SOC concentrations. The NOM fraction competing with the weakly adsorbing SOC (asulam) constituted a larger percentage of the total NOM than that competing with the strongly adsorbing SOCs. Although the adsorptive capacities of the SOCs were greatly reduced in water containing NOM compared with those in pure water, the change in the pore diffusion coefficient was insignificant. Therefore, NOM competed with the SOCs for adsorption sites, reducing the adsorptive capacity, but the amount of NOM loading was not so severe that it blocked or filled the pores, hindering the internal diffusion of the SOCs.     

Direct observation of solid-phase adsorbate concentration profile in powdered activated carbon particle to elucidate mechanism of high adsorption capacity on super-powdered activated carbon

Decreasing the particle size of powdered activated carbon (PAC) by pulverization increases its adsorption capacities for natural organic matter (NOM) and polystyrene sulfonate (PSS, which is used as a model adsorbate). A shell adsorption mechanism in which NOM and PSS molecules do not completely penetrate the adsorbent particle and instead preferentially adsorb near the outer surface of the particle has been proposed as an explanation for this adsorption capacity increase. In this report, we present direct evidence to support the shell adsorption mechanism. PAC particles containing adsorbed PSS were sectioned with a focused ion beam, and the solid-phase PSS concentration profiles of the particle cross-sections were directly observed by means of field emission-scanning electron microscopy/energy-dispersive X-ray spectrometry (FE-SEM/EDXS). X-ray emission from sulfur, an index of PSS concentration, was higher in the shell region than in the inner region of the particles. The X-ray emission profile observed by EDXS did not agree completely with the solid-phase PSS concentration profile predicted by shell adsorption model analysis of the PSS isotherm data, but the observed and predicted profiles were not inconsistent when the analytical errors were considered. These EDXS results provide the first direct evidence that PSS is adsorbed mainly in the vicinity of the external surface of the PAC particles, and thus the results support the proposition that the increase in NOM and PSS adsorption capacity with decreasing particle size is due to the increase in external surface area on which the molecules can be adsorbed.     

粉末活性炭对邻苯二甲酸二乙酯的吸附性能研究

考察了投加粉末活性炭吸附去除水中邻苯二甲酸二乙酯的可行性,并采用Freundlich公式拟合纯水和原水条件下的等温吸附方程。试验结果表明,采用粉末活性炭可有效去除水中邻苯二甲酸二乙酯,活性炭投加量为30mg／L,吸附120min后,纯水和原水条件下邻苯二甲酸二乙酯去除率分别为93．3％和89．3％。根据吸附等温方程计算得出,以邻苯二甲酸二乙酯的标准限值（0．3mg／L）为平衡浓度,纯水、原水条件下最大投炭量（80mg／L）可应对的邻苯二甲酸二乙酯最高质量浓度分别为7．575和5．731mg／L。     

Biological regeneration of powdered activated carbon added to activated sludge units

Powdered activated carbon equilibrium concentrations of 0, 50, 300 and 1000 mg l⁻¹ were studies in plug-flow activated sludge units maintained at sludge ages of 3, 5, 10 and 15 days. It was noted that the percentage removal of the effluent organic matter with respect to that of a control unit increased with increasing carbon equilibrium concentration. At a given activated carbon equilibrium concentration the COD removal tended to be independent of sludge age. Freundlich isotherms showed that the apparent adsorptive capacity gradually increased with increasing solids retention time, possibly caused by partial biological regeneration of the carbon. The regeneration is determined by the ratio of biological solids to carbon solids. A preliminary model was formulated to describe the relation between the daily regenerated adsorptive capacity and influent organic matter concentration.     

p-Nitrophenol removal by combination of powdered activated carbon adsorption and ultrafiltration - comparison of different operational modes

Ultrafiltration is classified as a low-pressure membrane technology which effectively removes particulate matter and microorganisms and to a certain extent dissolved organic matter (15-25%) and colour. The technology has been optimized and is becoming competitive compared to conventional processes for larger scale plant capacities. In combination with activated carbon it is an effective barrier regarding the removal of synthetic organic chemicals. Growing interest in ultrafiltration raises the question of better usage of the adsorption capacity of powdered activated carbon (PAC) used in combination with this low-pressure membrane technique. This paper presents a pilot plant study of different PAC dosing procedures within a combined hybrid membrane IN/OUT process for removal of p-nitrophenol (PNP) from water (c(0)=1mg/L) under real case conditions (e.g. usage of the same module for the whole duration of the experiment, backwashing with permeate water, no separate saturation of the membrane with substance without presence of carbon). p-Nitrophenol was chosen as an appropriate test substance to assess the efficiency of different operation modes. Dead-end and cross-flow filtration were compared with respect to different PAC dosing procedures: continuous dosing into a continuously stirred tank reactor (CSTR) in front of the module and direct dosing into the pipe in front of the module (continuous, single-pulse and multi-pulse dosing). There was no advantage in cross-flow mode over dead-end referring to PNP concentration in the permeate. Relating to the carbon dosing procedure, the best results were obtained for continuous PAC addition. The option of dosing directly into the pipe has the advantage of no additional tank being necessary. In the case of single-pulse dosing, the formation of a carbon layer on the membrane surface was assumed and an LDF model applied for a simplified estimation of the "breakthrough behaviour" in the thus formed "PAC filter layer".     

Application of powdered activated carbon for the adsorption of cylindrospermopsin and microcystin toxins from drinking water supplies

Cylindrospermopsin (CYN) and microcystin are two potent toxins that can be produced by cyanobacteria in drinking water supplies. This study investigated the application of powdered activated carbon (PAC) for the removal of these toxins under conditions that could be experienced in a water treatment plant. Two different PACs were evaluated for their ability to remove CYN and four microcystin variants from various drinking water supplies. The removal of natural organic material by the PACs was also determined by measuring the levels of dissolved organic carbon and UV absorbance (at 254 nm). The PACs effectively removed CYN and the microcystins from each of the waters studied, with one of the PACs shown to be more effective, possibly due to its smaller particle diameter. No difference in removal of the toxins was observed using PAC contact times of 30, 45 and 60 min. Furthermore, the effect of water quality on the removal of the toxins was minimal. The microcystin variants were adsorbed in the order: MCRR > MCYR > MCLR > MCLA. CYN was found to be adsorbed similarly to MCRR.     

The impact of aromatic compounds on the efficiency of biofiltration through activated carbon

The article has investigated the sorption process on activated carbon of aromatic compounds with different functional groups (o- nitrophenol, o-aminophenol, aniline). We have showed the possibility of assessing the efficiency of biofiltration depending on such factors as the variation of the Gibbs free energy of adsorption of sorbates and the value of the specific load of an organic substance on activated carbon. For determining a contribution of the biological component to the total efficiency of the process we used the value of the ratio between the specific dynamic adsorption to the specific equilibrium adsorption at uniform loads in terms of the organic matter on biologically activated carbon.     

粉末活性炭对水中呋喃丹的吸附性能研究

考察了粉末活性炭吸附去除水中呋喃丹的可行性,并采用Freundlich公式拟合去离子水和自来水条件下的吸附等温方程.结果表明,采用粉末活性炭可有效去除水中的呋喃丹,在去离子水条件下,呋喃丹初始质量浓度为0.035 mg/L,投炭量为20 mg/L,吸附时间为120 min时,呋喃丹的去除率大于98％.根据吸附等温方程计...