Adsorption Capacity Of Granular Activated Carbon Research Articles

Efficiency of GAC for Treatment of Leachate from Soil Washing Process

Granular activated carbon (GAC), granular activated alumina (GAA) and a ferric chloride solution (FCS) were tested for the treatment of leachate contaminated by heavy metals. The leachate was collected following the remedation of soils using weak organic acids and/or their salts, EDTA and DTPA. Only GAC was found to effectively remove heavy metals (Cd, Cu, Cr, Hg, Mn, Pb and Zn as chelates) from the leachate. At optimum pH ranging from 5.4 to 6.9, 97% of Hg was removed while at optimum pH ranging from 6.9 to 7.7, 78 to 96% of Cd, Cu, Mn, Pb and Zn were removed. Some 77% of the Cr was removed at optimum pH of 5.4. Adsorption rate constant and Langmuir adsorption capacity of GAC were found to be 0.01 min−1 and 19 mg metal chelate g−1 of GAC, respectively. Freundlich constants, k and n were found to be 21 mg g−1 and 2.778, respectively. The brown color of the leachate turned colorless after GAC treatment.

Effect of ozonation on preloading of background organic matter in granular activated carbon filters

Background Organic Matter (BOM) preloading is adsorption of BOM onto Granular Activated Carbon (GAC) prior to the adsorption of target compounds, such as pesticides and other organic micropollutants (e.g. atrazine). BOM preloading is commonly found to speed up the breakthrough of target compounds during GAC filtration. Ozonation of GAC filter influent may be expected to lower BOM preloading, because it results in less adsorbable and more biodegradable BOM compounds. Short Fixed Bed (SFB) tests with virgin and preloaded GAC, performed within this study, confirmed that preloading of BOM present in pretreated river Rhine water speeds up the breakthrough of atrazine in GAC filters. BOM preloading was found to lower equilibrium adsorption capacity of GAC for atrazine, and to slow down both external and internal mass transfer rate of atrazine on/into GAC. Adsorption capacity of (crushed) GAC was determined from atrazine adsorption isotherms, while mass transfer rate coefficients were determined by fitting the Homogeneous Surface Diffusion model to the breakthrough of atrazine in the SFB tests. More pronounced BOM preloading was found in the GAC filter receiving non-ozonated influent than in its ozonated counterpart. Biodegradation of ozonated BOM was shown to lower BOM preloading in GAC filters.

Effects of molecular oxygen on GAC adsorption of energetics

Munitions wastewaters are commonly treated by granular activated carbon (GAC) adsorption followed by incineration of the spent carbon. The design of effective GAC unit processes hinges on the knowledge of GAC adsorption capacity for the compounds of interest as well as the types of chemical interactions to expect. GAC can often catalyze polymerization or chemical degradation of the adsorbate in the presence of molecular oxygen. Some adsorbates, though less common, may be subject to catalytic activity even when no molecular oxygen is present. The products of these interactions may enhance or interfere with effective waste treatment. This study individually evaluated the adsorption properties of a variety of energetics compounds. A number of surface catalyzed polymerization and degradation reactions were noted.

Effect of ozonation on preloading of background organic matter in granular activated carbon filters

Background Organic Matter (BOM) preloading is adsorption of BOM onto Granular Activated Carbon (GAC) prior to the adsorption of target compounds, such as pesticides and other organic micropollutants (e.g. atrazine). BOM preloading is commonly found to speed up the breakthrough of target compounds during GAC filtration. Ozonation of GAC filter influent may be expected to lower BOM preloading, because it results in less adsorbable and more biodegradable BOM compounds. Short Fixed Bed (SFB) tests with virgin and preloaded GAC, performed within this study, confirmed that preloading of BOM present in pretreated river Rhine water speeds up the breakthrough of atrazine in GAC filters. BOM preloading was found to lower equilibrium adsorption capacity of GAC for atrazine, and to slow down both external and internal mass transfer rate of atrazine on/into GAC. Adsorption capacity of (crushed) GAC was determined from atrazine adsorption isotherms, while mass transfer rate coefficients were determined by fitting the Homogeneous Surface Diffusion model to the breakthrough of atrazine in the SFB tests. More pronounced BOM preloading was found in the GAC filter receiving non-ozonated influent than in its ozonated counterpart. Biodegradation of ozonated BOM was shown to lower BOM preloading in GAC filters.

Effects of molecular oxygen on gac adsorption of energetics

Munitions wastewaters are commonly treated by granular activated carbon (GAC) adsorption followed by incineration of the spent carbon. The design of effective GAC unit processes hinges on the knowledge of GAC adsorption capacity for the compounds of interest as well as the types of chemical interactions to expect. GAC can often catalyze polymerization or chemical degradation of the adsorbate in the presence of molecular oxygen. Some adsorbates, though less common, may be subject to catalytic activity even when no molecular oxygen is present. The products of these interactions may enhance or interfere with effective waste treatment. This study individually evaluated the adsorption properties of a variety of energetics compounds. A number of surface catalyzed polymerization and degradation reactions were noted.

Evaluation of granular activated carbon for removal of trace organic compounds in drinking water

Drinking water supply from Feng Yuan waterworks was studied by bench-scale experiments examining effects of different particle size of granular activated carbon (GAC), pH, dosage, and temperature, and by forming the Freundlich adsorption model. The adsorption performance could be significantly improved by using small-size GAC, low pH, low temperature, and an increase in the dosage of GAC. The use of the Freundlich adsorption, model had the potential in evaluating the behavior of GAC. The results reflected the better adsorption efficiency of GAC in the higher initial concentration of total organic carbon (TOC) from the drinking water source. In addition, the adsorption capability (q e) and the Freundlich constant (n) increased with increasing operation time. In a single column study, a low flow rate led to an increase in adsorption capacity and breakthrough time and a decrease in the treated water volumes. In the next step, the bed depth/service time or BDST design method was used to predict the breakthrough profiles for TOC in the four serial columns. The column service time and treated water volumes were all reduced while high adsorption efficiency of GAC could be achieved. Furthermore, the operation at a low flow rate improved the adsorption capacity (N o) of GAC for the same TOC removal percentages.

Biological Colonization of Granular Activated Carbon Filters in Drinking‐Water Treatment

A study of biological filtration on granular activated carbon (GAC) has been performed at the Neuilly‐sur‐Marne (France) treatment plant using experimental pilot filters. Bacterial colonization of GAC was monitored in three carbon filters having varying depths and filtration velocities, but similar empty bed contact time (EBCT). About three months were required to colonize the GAC in the filters and a steady state bacterial biomass of around 2 μgC/cm3 GAC was reached. During the colonization period, removal of nonbiodegradable organic carbon (NBDOC) by filtration decreased from 50% to less than 10% showing a gradual saturation of GAC adsorption capacity. However, biological processes take turn with adsorption to ensure a significant removal of biodegradable dissolved organic carbon (BDOC) during the study period (more than 200 days). Filters operating under different conditions did not show any difference in the BDOC removal. This indicates that biological removal of organic matter in GAC filters having a given EBCT is independent of filtration rate (in the range 6 m/h–18 m/h). The maximum bacterial density in the filter effluent water was 1.5×105bacteria/mL during the colonization phase; this seemed to be linked to a lag in establishing a protozoan population, which, at equilibrium, efficiently removed bacterial biomass produced within the filters. Once established, the efficiency of this complex microbial assemblage was remarkable; the removal of about 0.25 mgC/L of BDOC resulted in the release of less than 0.5×105bacteriapermillileter, around 0.0015 mgC/L as bacterial biomass in the effluent.

Comparative study of adsorption capacity of various adsorbents for treating dye wastewaters

The objective of this laboratory study was to determine the effect of dosage, contact time and type of adsorbents on the color and COD (chemical oxygen demand) removal for dye wastewaters. The adsorption parameters for Langmuir and Freundlich isotherms and mass transfer coefficients from bulk solution to particle surfaces for disperse dye were also determined. The adsorbents used in this study included powdered activated carbon (PAC), granular activated carbon (GAC), activated alumina, molecular sieves, diatomite, and sawdust. For an initial dye concentration of 150 ppm and adsorbent dosage of 15 g/1 and a contact time of 2 hours, the COD removal efficiency was 98%, 60–65%, and 24–30%, for PAC, activated alumina, and molecular sieves, respectively. The order of adsorbent efficiency was found to be: PAC > activated alumina > molecular sieves > GAC > diatomite. The adsorption capacity of diatomite and GAC was very poor. The color removal (color difference or AE∗ab) varied from 45 to 55 for most adsorbents s...

Molecular oxygen and the adsorption of phenols—effect of functional groups

ABSTRACT: This study reveals that the presence of molecular oxygen (oxic conditions) has a significant impact on the exhibited adsorptive capacity of granular activated carbon (GAC) for several phenolic compounds. The increase in the GAC adsorptive capacity under oxic conditions results from polymerization of these adsorbates on the carbon surface. The mechanism of polymer formation is through oxidative coupling of phenolic molecules. The extent of an increase in the GAC adsorptive capacity is in accordance with the ease of oxidation of these compounds. However, substituting a nitro group on the parent phenol molecule suppressed polymerization reactions and no increase in the GAC adsorptive capacity was observed under oxic conditions for these substituents.

Operating capacity of GAC adsorbers—dissolved oxygen and extended service life

ABSTRACT: The effect of molecular oxygen on the adsorptive capacity of activated carbon was evaluated in this study. It was determined that the capacity of granular activated carbon (GAC) for o‐cresol under oxic conditions can be more than 2.5‐fold the capacity attainable under anoxic conditions. This increase in the GAC adsorptive capacity under oxic conditions cannot be attributed to biological activity. The observed phenomenon was found to result from carbon mediated polymerization reactions of o‐cresol that occur in the presence of molecular oxygen. The rate of adsorbate polymerization was slower than the rate of adsorption and the presence of molecular oxygen did not affect adsorption kinetics during the initial phase of adsorbent‐adsorbate contact. However, the presence of molecular oxygen was demonstrated to have a significant impact on the breakthrough of o‐cresol from 5 GAC adsorbers operated in series (total bed length = 4 m, total GAC mass = 1 kg). During the first phase of the experiment, which was conducted under anoxic conditions, breakthrough of o‐cresol from all 5 adsorbers was accurately predicted using a plugflow homogeneous surface‐diffusion model and independently determined kinetic and capacity parameters. Furthermore, the effluent profiles collected under anoxic conditions exhibited almost no tailing during the later part of breakthrough as saturation was approached. On introduction of oxygen to this system the effluent o‐cresol concentration dropped significantly (from 200 mg/L to only 6 mg/L). The total exhibited GAC adsorptive capacity for the entire experiment was accurately predicted by the oxic adsorption isotherm.

Role of dissolved oxygen on the adsorptive capacity of activated carbon for synthetic and natural organic matter

Parameters affecting the adsorptive capacity of granular activated carbon (GAC) for o-cresol, phenol, o-chlorophenol, 3-ethylphenol, trichloroethylene, and natural organic matter are investigated in this study. Experimental results prove that the presence of molecular oxygen significantly increases the adsorptive capacity of GAC for five of these six compounds. The oxic GAC adsorptive capacity for o-cresol, for example, can be up to 2.6-fold the capacity that is attainable under anoxic conditions

Evaluating Layered Upflow Carbon Adsorption for the Removal of Trace Organic Contaminants

The primary objective of this investigation was to compare layered upflow carbon adsorption (LUCA) with conventional fixed‐bed adsorbers for removing chlorinated hydrocarbons from drinking water sources. During LUCA operation, the granular activated carbon (GAC) is added in thin layers, with a new layer being added whenever the maximum allowed effluent concentration of the contaminants is reached. Thus, the time of exposure of the GAC to dissolved organic carbon, which is known to reduce GAC's adsorption capacity for organic contaminants, is reduced. This mode of operation was found to produce approximately 50 percent longer operating times and correspondingly higher throughputs.

Evaluating GAC adsorptive capacity

Potential sources of error in evaluating the adsorptive capacity of granular activated carbon (GAC) are identified and discussed, with special attention given to carbon sampling and preparation, preparation of test solutions, and selection of GAC dosages, adsorbate concentration, and equilibration time. Adsorptive capacity can vary with particle size, but data are presented to show that this may not always occur. Heterogeneous solutions require careful selection of GAC dosages and adsorbate concentration, and the data for such solutions require careful interpretation. Model simulations are used to illustrate the importance of closely approaching equilibrium and to estimate the time required to approach equilibrium under various conditions. For large GAC particles and slowly diffusing adsorbates, several years may be required to reach equilibrium. Failure to reach equilibrium can result in a significant underestimation of adsorptive capacity. Pulverizing GAC greatly reduces the time required to reach equilibrium, thus reducing the possibility of biodegradation of the adsorbate.