Carbon Adsorption in Water Treatment

Adsorption is the process by which liquid or gaseous molecules are concentrated on a solid surface, in this case activated carbon. This is different from absorption, where molecules are taken up by a liquid or gas. Activated carbon can made from many substances containing a high carbon content such as coal, wood and coconut shells. The raw material has a very large influence on the characteristics and performance activated carbon. 

The term activation refers to the development of the adsorption properties of carbon. Raw materials such as coal and charcoal do have some adsorption capacity, but this is greatly enhanced by the activation process. There are three main forms of activated carbon. 

Activated carbon has the strongest physical adsorption forces or the highest volume of adsorbing porosity of any material known to mankind. 

Activated carbon is also available in special forms such as a cloth and fibres. Activated Charcoal Cloth (ACC) represents a family of activated carbons in cloth form. These products are fundamentally unique in several important ways compared with the traditional forms of activated carbon and with other filtration media that incorporate small particles of activated carbon. Developed in the early 1970 s ACC products are 

Gas Phase Adsorption - This is a condensation process where the adsorption forces condense the molecules from the bulk phase within the pores of the activated carbon. The driving force for adsorption is the ratio of the partial pressure and the vapour pressure of the compound. 

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Sztark W. Methods of studies rewiev of activated carbon adsorptivity in water treatment. Conf.. .Activated carbon , Zakopane 1980. 

Chapter 6 Activated Carbon Adsorption in Water Treatment.437... 

Discuss how carbon adsorption works and how it can be used in water treatment applications. Give some specific examples where this technology is used to remove specific contaminants. 

The most common application of carbon adsorption in municipal water treatment is in the removal of taste and odor compounds. Figure 12 provides an example of a process flow diagram for a municipal water treatment plant. In this example water is pumped from the river into a flotation unit, which is used for the removal of suspended solids such as algae and particulate matter. Dissolved air is the injected under pressure into the basin. This action creates microbubbles which become attached to the suspended solids, causing them to float. This results in a layer of suspended solids on the surface of the water, which is removed using a mechanical skimming technique. Go back to Chapter 8 if you need to refresh your memory on air flotation systems. 

Carbon adsorption is preferably used in water treatment... 

Steam regeneration is most commonly applied to activated carbon that has been used in the removal and/or recovery of solvents from gases. At volatile organic compound (VOC) concentration levels from 500 to 15,000 ppm, recovery of the VOC from the stream used for regeneration is economically justified. Below about 500 ppm, recovery is not economically justifiable, but environmental concerns often dictate adsorption followed by destruction. While activated carbon is also used to remove similar chemicals from water and wastewater, regeneration by steam is not usual. The reason is that the water-treatment carbon contains 1 to 5 kg of water per kg of adsorbent that must be removed by drying before regeneration or an excessive amount of superheated steam will be needed. In water treatment. 

It has long been known that, under appropriate conditions and especially in the liquid phase, synergistic associations can develop between microbiological systems and activated carbons or other support media (e.g.. in trickling bed filters for aerobic water treatment). In liquid phase applications, bacterial colonization of activated carbon can occur quite readily [76-79]. For example, the adsorptive capacities of activated carbon beds used in water treatment are often greatly enhanced by the presence of microorganisms, and the useful filter life is extended beyond that expected for a process of purely physical adsorption. Essentially, the... 

According to the above, most tested carbons may be used as filter beds in water treatment plants. The choice of carbon should be carried out on the basis of indicators, analysis of costs, possibiUty and rate of regeneration. Adsorption capacity and parameters of work should be determined by pilot scale studies. Studies of testing methods and model adsorption should give standard carbons for removal of characteristic groups of water pollutants. Both powdered and granular carbons should be used, the former to pre—treatment or periodically at the time of peak load, and the latter, to final water treatment in compensated conditions. 

Activated carbons should be selected on the basis of different model substances and then tested in dynamic conditions. Analysis of adsorption isotherms and curves of filter breakthrough gives a lot of information about adsorption and kind of diffusion. Carbon selected for water treatment should be tested in real conditions of semi—technical scale. 

The history of SPE dates from more than fifty years ago, with granulated active carbons previously used in water treatment technologies. The pioneer work was conducted by the U.S. Public Health Service (Cincinnati, OH). After that, other approaches were investigated with petroleum pollutants, insecticides and VOCs. Disadvantages such as irreversible adsorption, analyte reactions on the activated carbon surface and low recoveries started research in new sorbent materials. See the historical review of SPE by I. Liska. ... 

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