**3. The kind and characteristics of sorbents**

It is well known that alkali sorbents such as CaO, CaCO3, Ca(OH)2, NaOH, Na2CO3, NaHCO3, KOH, MgO, Mg(OH)2, dolomites, and dolomite limestones(CaCO3/MgCO3) are used to remove SO2 and acid gases in the flue gas cleaning processes (Kunio et al., 1994; Jonas et al., 1984; Jung et al., 2000). Under these sorbents, calcium-based alkali sorbents are the most widely used to remove SO2. Because calcium-based sorbents have good reactivity toward acidic gases and lower cost compared to other sodium-based alkali adsorbent.

The sorbent should be selected in consideration of the most important factors, hygroscopicity and price. Sodium-based sorbents have better removal efficiency of pollutant gases but is more expensive than calcium-based sorbents. While calcium-based sorbents exhibit hygroscopicity, but sodium-based sorbents deliquescency. In Table 2, various sorbents frequently used in flue-gas desulfurization processes are compared and the physical properties of the sorbents are also described as a part of basic research to understand whether they are utilized in flue-gas desulfurization processes. In addition, in Table 3 the molecular weight, specific gravity, density, decomposition temperature, melting point, particle size, solubility, and maleficence of the sorbents frequently used in flue-gas desulfurization processes are presented.

**2.2.3 Application to waste water treatment (nitrogen, phosphorous, heavy metals, pH** 



Recycling of waste oyster shells has much limitation in environmental engineering. First, the quantity of waste oyster shells is too much to be recycled in environmental engineering. Second, a plan to retreat the waste oyster shells contaminated after adsorption of heavy metals should be prepared above all. Third, recycling of waste oyster shells would require removal of impurities through proper processing and treatment through a calcination process, which decreases the economic feasibility. Fourth, the repeated use lowers the

It is well known that alkali sorbents such as CaO, CaCO3, Ca(OH)2, NaOH, Na2CO3, NaHCO3, KOH, MgO, Mg(OH)2, dolomites, and dolomite limestones(CaCO3/MgCO3) are used to remove SO2 and acid gases in the flue gas cleaning processes (Kunio et al., 1994; Jonas et al., 1984; Jung et al., 2000). Under these sorbents, calcium-based alkali sorbents are the most widely used to remove SO2. Because calcium-based sorbents have good reactivity toward acidic gases and lower cost compared to other sodium-based alkali adsorbent.

The sorbent should be selected in consideration of the most important factors, hygroscopicity and price. Sodium-based sorbents have better removal efficiency of pollutant gases but is more expensive than calcium-based sorbents. While calcium-based sorbents exhibit hygroscopicity, but sodium-based sorbents deliquescency. In Table 2, various sorbents frequently used in flue-gas desulfurization processes are compared and the physical properties of the sorbents are also described as a part of basic research to understand whether they are utilized in flue-gas desulfurization processes. In addition, in Table 3 the molecular weight, specific gravity, density, decomposition temperature, melting point, particle size, solubility, and maleficence of the sorbents frequently used in flue-gas

**2.2.4 Improvement of sludge dehydration capacity (digested sludge etc.)** 

mixture reduces the required dehydration time.

**2.2.5 Others (calcination, red tide, coagulation, fertilizer, etc.)** 


**neutralization, etc.)** 

prepared.

**2.3 Recycling limitation** 

efficiency below commercial products.

desulfurization processes are presented.

**3. The kind and characteristics of sorbents** 


Table 2. Characteristics of selected sorbents.


Table 3. Characteristics of sorbents in FGD process.
