Adsorption system, carbon wastewater treatment

In addition to anionic species, some metal cations can also be removed via adsorption processes with LDH materials. Recently, Lazaridis reported an interesting removal of two anions (P04 , SCN ) and three cations (Cd , Pb ", Ni " ) from aqueous solutions in single batch systems using uncalcined and calcined (773 K) Mg/Al LDH carbonate materials [148]. It was found that the calcined material showed higher sorption capacities than the uncalcined material for all the ions. Since the sorption capacities are relatively high, the author suggested that LDHs could be considered as a potential materials for sorption of both anions and cations in wastewater treatment systems. Seida et al. have also reported the rapid removal of dilute Pb from dilute aqueous solutions by a column packed with a pyroaurite-like Mg/Fe-COs LDH compound over a wide range of space velocity (Sv = 150-800 min" ) [149]. 

Activated carbon adsorption is a well-established process for adsorption of organics in wastewater, water, and air streams. Granular activated carbon (GAG) packed in a filter bed or of powdered activated carbon (PAG) added to clarifiers or aeration basins is used for wastewater treatment. In the pesticide industry, GAG is much more widely used than PAG. Figure 10 shows the process flow diagram of a GAG system with two columns in series, which is common in the pesticide industry [11]. 

That carbon adsorption is deemed a suitable technology for a variety of water and wastewater treatment applications is evidenced by the substantial shift of the technology from pilot to full scale implementation over the past decade. However, and particularly in the case of wastewaters, it is difficult to generalize or extrapolate system design from one situation to another, even within a given... 

There are many methods for the desulfurization of nature gas, which can be classified into dry desulfurization, wet desulfurization, and catalytic adsorption. In the dry desulfurization, some solid sorbents, such as iron oxide, zinc oxide, activated carbon (AC), zeolites, and molecular sieves, are used. In wet desulfurization method, liquid-phase chemical/physical solvent absorption systems are usually used for scrubbing H2S amine-based processes are subject to equipment corrosion, foaming, amine-solution degradation, and evaporation, and require extensive wastewater treatment. As a result, this sulfur removal technology is complex and capital intensive,44 although the processes are still employed widely in the industry. The desulfurization of coal gasification gas will be reviewed in detail in Section 5.5. In the catalytic-adsorption method, the sulfur compounds are transformed into H2S by catalytic HDS or into elemental sulfur or SOx by selective catalytic oxidation (SCO), and then, the reformed H2S and SOx are removed by the subsequent adsorption. 

Activated carbon is the most important carbon material used to adsorb organic solutes from aqueous solutions, although the use of activated carbon fibers and activated carbon cloths has been continuously growing in recent years. These carbon materials are applied across a wide spectrum of systems such as drinking water and wastewater treatments and are used in the food, beverage, pharmaceutical, and chemical industries. Furthermore, activated carbon adsorption has been cited by the US Environmental Protection Agency as one of the best available environmental control technologies [1]. 

In wastewater treatment, carbon adsorption systems often use granular activated carbon. The design of the activated carbon system consists essentially in determining ... 

A third plant uses a chemical precipitation step for removing arsenic and zinc from contaminated surface water runoff. Ferric sulfate and hme are alternately added while the wastewater is vacuum-filtered and sludge is contract-hauled. The entire treatment system consists of dual-media filtration, carbon adsorption, ion exchange, chemical precipitation, and vacuum hltration. Sampling results across the entire treatment system indicated that arsenic was reduced from 6.9 to 0.2 mg/L and zinc from 0.34 to 0.11 mg/L. 

Powdered activated carbon may also be coupled to ultrafiltration (UF). This hybrid system, referred to in the literature as the PAC/UF process, incorporates the adsorption capabilities of activated carbon and the microorganism and particle removal ability of the UF membranes [71]. Combined with coagulation as a pre-treatment, tlie coupling has been successfully applied to the treatment of domestic wastewater [72]. Mdtivier-Pignon et al. [73] have proposed a combination of ultrafiltration with activated carbon cloth to treat complex aqueous solutions with suspended solids, colloids and dissolved organic molecules, like highly colored wastewaters from ink manufacture. 

One example (out of many) to illustrate the complexity of adsorption from solution (as compared with gas-phase adsorptions), is the removal of mercury, an unacceptable toxic pollutant in aqueous systems. It is found in wastewaters (before treatment) from such manufacturing industries as chloroalkali, paper and pulp, oil refining, plastic and batteries, and can exist as free metal, as Hg(I) and Hg(II). Mercury adsorption capacity, on AC, increases as the pH of the aqueous systems decreases. Carbons with different activation methods have widely different capacities. Sulfurization of the carbon, loading the carbon with zirconium, as well as the dispersion of FeOOH species over the carbon, enhanced Hg(II) uptake. Mercury vapor can be taken up using AC which have been pre-treated with sulfur, the effect of chemisorbed oxygen being to retard (not prevent) the uptake of mercury, Lopez-Gonzalez et al. (1982). 

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