**2. Environmental problems of oyster shells and utilization plans for each field**

#### **2.1 Environmental problems caused by oyster shells**

Environmental problems caused by waste oyster shells were as follows [Kim, 2007]; i) increase of waste, ii) pollution of marine eco-system due to illegal landfill, iii) increase of

Steel Corp., 1993), sludge conditioners (Lee et al., 2001), eutrophication control (Kwon et al., 2004), filtering medium (Park and Polprasert, 2008), catalyst (Nakatani et al., 2009), soil conditioner (Lee et al., 2008a,b), and desulphurization sorbents (Jung et al., 2000) have been reported. The desulphurization system can be divided into three groups such as dry adsorption (Garea et al., 2001), wet scrubbing (Chu et al., 1997), and wet/dry system

Year Oyster Production(ton) Estimated Generation of Oyster

1997 17,210 258,150 1998 9,905 148,575 1999 11,690 175,350 2000 15,939 239,085 2001 10,056 150,840 2002 7,950 119,250 2003 20,201 303,015 2004 25,690 385,350 2005 27,320 409,800 2006 31,016 465,240

Table 1. Oyster production and estimated generation of oyster shells in Korea.

is an acidic gas, the use of waste shells as mixed sorbents is judged to be feasible.

The research on application of oyster shells to a sorbent for incineration and desulfurization is judged to be very helpful in preserving marine eco-system, preventing the damage of natural landscape and solving health/sanitation problem. Therefore, new applications utilizing these wasted oyster shells are expected to contribute towards recycling consciousness within the society [Asaoka et al., 2009]. The application of many kinds of waste shells, which have been dried, crushed and calcined, to sorption of acidic gases and nitrogen oxides is not only economically valuable but also very significant in the aspect of waste recycling. In addition, considering that chlorine which has been found to be a precursor of such toxic organic substances as dioxin and furan lately creating social concerns

In this research, we are going to provide a basic data to a process for removing both sulfur oxides and nitrogen oxides at the same time from exhaust gases. For this purpose, first of all, the basic physical and chemical properties of waste oyster shells were investigated. In addition, the calcination and hydration reaction of waste oyster shells were experimented and the preparation method of sorbents was investigated. In order to investigate the feasibility of using oyster shells as a sorbent for removal of sulfur and nitrogen oxides, the performance of prepared sorbents was compared for understanding reaction characteristics

**2. Environmental problems of oyster shells and utilization plans for each field** 

Environmental problems caused by waste oyster shells were as follows [Kim, 2007]; i) increase of waste, ii) pollution of marine eco-system due to illegal landfill, iii) increase of

Shells(ton)

(O'Dowd et al., 1994).

using a fixed bed reactor.

**2.1 Environmental problems caused by oyster shells** 

bad smell due to negligence, iv) a huge amount of treatment expense, and v) weak demand on recycled materials (fertilizer, etc.) from oyster shells. Fig. 1 shows the generation process of waste oyster shells. Oyster meat is consumed and a significant amount of waste oyster shell is discarded.

Fig. 1. Generation steps of the waste oyster shells.

### **2.2 Recycling plan of oyster shells on the aspect of environmental engineering**

Environmental engineering research on recycling of oyster shells has been somewhat conducted in China and Japan, but most of the research has focused on the purpose of water purification in a limited scope [Kim, 2007].

### **2.2.1 Removal of air pollutants (SO2, H2S, CO2, HCl, NOx, etc.) from the exhaust gases**


#### **2.2.2 Soil improvement (acidity reduction, organics adsorption) and adsorption of heavy metals**


Reuse of Waste Shells as a SO2/NOx Removal Sorbent 305

NaOH Yes Yes Spray Drying, Wet Scrubbing, Dry

CaCO3 No Yes Spray Drying, Wet Scrubbing, Dry

No Yes FGD absorbent

Ca(OH)2 No Yes Wet Scrubbing, Dry Scrubbing CaO No Yes Spray Drying, Wet Scrubbing, Dry

Sorbent Description CaCO3 CaO Ca(OH)2 NaHCO3 Na2CO3 NaOH Molecular Weight 100 56.08 74.09 84 106 40 Specific Gravity 2,93 3.37 2.24 - 2.53 2.13 Bulk Density(ton/m3) 1.11 - 1.7~2.3 - 2.08 -

Temp.(℃) 898 - 580 - - -

Melting Point(℃) - 2,572 - - 851 318.4 Size of Particle(㎛) 4~44 - 4~100 - >100 -

at 20℃) 0.0014 - 0.185 7.1 6.9 - Impact of Human low low low low low large

The seashells of oyster, hard-shelled mussel, clam, and seashell from Tong Young province around South Sea in Korea were used as a main material. Salts and other organic substances were removed by washing and drying the waste seashells. Limestone from Danyang and Jungsun province in Korea was adapted for comparison of physicochemical properties of oyster shells. All the materials were crushed 2 times by Jaw crusher and Ball mill after drying enough. The physical and chemical characteristics of the waste oyster shells were analyzed by ICP (ICPS-7500 Shimadzu, Japan), SEM (JEOL superprobe JSM-5400, USA), XRD (SIMENS, Deutsche), and BET surface area (Micromeritics Co., USA). ICP was applied to analyze the atomic properties of the materials. SEM was used to observe the microtissue of the surface of wasted shells. Surface area of the sorbents was measured by BET technique

Scrubbing

Scrubbing

Scrubbing

Sorbent Deliquescent Hygroscopic Application

Na2CO3 Yes Yes Spray Drying NaHCO3 Yes Yes Dry Scrubbing

**Waste oyster shells (WOS)** 

Decomposition

Solubility(g/100cc ,

**4. Materials and methods** 

Table 2. Characteristics of selected sorbents.

Table 3. Characteristics of sorbents in FGD process.

**4.1 Physicochemical analysis of oyster shells** 

#### **2.2.3 Application to waste water treatment (nitrogen, phosphorous, heavy metals, pH neutralization, etc.)**

