Powdered Activated Carbon Adsorption Tests

Example 2 (Powdered Activated Carbon Adsorption Tests) 

A wastewater contains 75 mg/L of TOC following biological treatment. EfQnent TOC gnide-lines reqnire that the waste must contain no more than 15 mg/L TOC prior to discharge. An 

Determine if the desired effluent TOC concentration can be achieved by carbon adsorption. 

Determine the adsorptive capacity of the carbon at this TOC concentration. 

Determine the ultimate capacity of the carbon for treating this wastewater. 

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Most kboratoiy tests are designed for evaluating powdered, activated carbons, with the adsorption isotherms, giving a rough first estimate of how well a carbon will perform in a given application. Data collected during an adsorption test will describe the performance of the carbon and will yield valuable information if properly mterpreted. 

In actual practice, powdered activated carbon is added to the wine or the must in amounts equal to about 0.05 to 1 g. of activated to each liter of wine, but to avoid loss of quality, the smallest effective dose should be used. The dose can be determined by laboratory tests on the wine. A suspension of carbon in a small amount of wine is first prepared and then added to the rest of the wine (must) contained in a vat. The adsorptive purification can be enhanced by stirring the contents of the vat or by bubbfing air fed at the bottom of the vat. This process takes several hours, after which the spent-up activated carbon can be separated by sedimentation followed by filtration in a filter press or in a centrifuge. 

Adsorption of As by AC can be improved by impregnation of AC emplo)dng suitable chemicals (e.g., sulfur contain textile dyes for As(III) and Fe(III) salts for removal of As(V) from aqueous solutions (Ansari, 2007). Recently, an interesting study was carried out by Ahna et al. (2013) on the As removal from water using activated carbon (AC). The authors tested different activated carbons modified with iron hydroxide for their ability to adsorb As from water. They concluded that iron modified activated carbons are efficient adsorbents for As at concentrations lower than 300 [xg. According to Mohan and Pittman (2007) Activated carbon can remove 60% As(V) and As(III) but this removal percentage of As is not sufficient to reach drinking water quality. However, sedimentation or filtration processes are required in case of powdered activated carbons, which in turn adds extra cost to the technology. 

Activated carbon is available in various forms, ranging ftxim light and fluffy powder to hard, dense granules. Besides classification into granular (GAC) and powdered (PAC), commercially available activated carbons are further divided into grades based on adsorptive, physical and chemical properties [6, 18]. Commonly used tests for activated carbons ai e summarized in Table 2. 

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