Activated Carbons are mostly used in absorption of wide variety of water pollutants or in water treatment because of its ability to improve water by removing disagreeable tastes and odors, including objectionable chlorine and many chemicals and dissolved gases, and in some cases it can be effective against microorganisms. Nevertheless this activated carbon will not affect total dissolved solids as unable by sorption, hardness, or heavy metals. Limited use of carbon filter systems have been certified for the removal of lead metal, asbestos, cysts, and coliform. Such activated carbon gets created from a variety of carbon-based bio-materials in a high-temperature process to create a matrix of millions of microscopic pores and crevices. Half kilo of activated carbon provides anywhere from 60 to 150 acres of aerial surface area to trap microscopic pollutants and large organics, while the activated surface areas cling to, or adsorb, small organic molecules.The ability of an activated carbon filter to remove certain microorganisms,organic especially pesticides, THMs (chlorine by-product), trichloroethylene (TCE), PCBs, depends upon several factors, like type of carbon and amount used, design of filter and flow rate, how long filter has in use, types of impurities filter has previously removed. Thus carbon adsorption process is controlled by diameter of pores in carbon filter and by diffusion rate of organics via pores. Adsorption rate is a function of molecular weight, molecular size .

Major Disadvantages of Adsorption process are

• Product recovery possibly requiring a special, expensive distillation (or extraction)

• Adsorbent progressively deteriorating in capacity as number of cycles increases

• Adsorbent regeneration requiring a steam or vacuum source

• Relatively high capital cost

• Prefiltering of gas stream possibly required to remove any particles capable of

plugging adsorbent bed

• Cooling of gas stream require to get usual range of operation temp (below 50C°)

• Relatively high steam requirements to desorb high-molecular-weight pollutants

• Spent adsorbent may be considered a hazardous waste

• Some contaminants may undergo violent exothermically with adsorbent (explosion danger).

In addition to Rajendras detailed answer

beside the very common use of a bed of adsorbent, addition of powdered activated carbon, clay, microsilica, lime is in use and may provide also sludge ballasting.

Towards your question of a combination with other processes, yes these are interesting and some are already in use, e.g. combination adsorption/biodegradation.

The potential of these combinations is mainly in the field of difficult to treat contaminants.

Thank you Rajendra and Dr.Titus for sharing your views... what could be the best process to couple with adsorption.. any studies in that context ? (apart from adsorption/biodegradation)

Apart from the thorough details aforementioned, one major drawback of adsorption technologies, especially if you are dealing with toxic compounds and/or micropollutants, is that what you actually achieve is to accumulate and transfer the pollution load from the aqueous to the adsorbent phase. You do not eliminate the pollutants but simply transfer the problem. On the contrary, chemical oxidation processes (conventional chemical processes such as Fenton reagent, permanganate, hypochlorite but also Advanced Oxidation Processes such as photocatalysis, eloctrochemical oxidation etc. ) are destructive techniques. A sequential treatment is often used by employing chemical oxidation initially to degrade toxic agents and possibly major oxidation by-products that could reduce the efficacy of the adsorption process and adsorption as a next step. Check indicatively Rodriguez et al., 2008 and Shon et al., 2005

See e.g. carbo-iron http://www.ufz.de/index.php?en=7038

Thank you Theodora Velegraki for sharing a critical point in adsorption process.

Thank you Dr. Titus, the link you posted was very interesting and very important for me. One of my understanding is that, it is challenging to remove certain kind of pollutants using adsorption process alone, in such cases, coupling chemical oxidation with adsorption is a wise option.

Please see the link suggested by Dr.Titus it's very useful

Regards

We have worked on the post-sorption valorization of biosorptionally treated wastewater by the integration technology approach. please have a look at it.

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