**1. Introduction**

Lately, many environmental pollution problems are taking place due to advancement of science and technology, enhancement of industry, rapid economic development, change of life style, and population increase. Not only in Korea but also worldwide consciousness of crisis over environmental pollution problems is spreading and especially countermeasures to solve the environmental pollution come into the limelight as concerns of the entire globe beyond any regions and nations. In the past, environmental pollutions including abnormal weather changes, global warming, El Nino, Ra Nina, ozone layer destruction, and marine pollution were issues of a limited area, but now they appear in fact as issues of the entire globe [Jung, 1999, 2008].

In the southern coast of Korea, a lot of oyster shells are dumped as a by-product of marine aquaculture industry. A large amount of oyster shells is a general waste fishermen should take care of but it seems difficult to handle it effectively due to the problems of securing of landfill sites and collection/transportation of oyster shells [Jung, 2005, 2007]. This waste piles up at coastal areas and causes many environmental problems including pollution of coastal fisheries, management problem of public water surface, damage of natural landscape, and health/sanitation problem.

In Japan, 200,000 tons of oysters were produced in 2007 [Asaoka et al., 2009]. And Table 1 shows oyster production of Korea from 1997 to 2006. On the basis of these data, generation of oyster shells is estimated on the average at 270,000 tons/year [Kim, 2007], and more than 50~70% of which was dumped into public waters and reclaimed lands, which cause an unpleasant fishy smell as a consequence of the decomposition of fresh remnant attached to oysters (Kim, 2007; Yoon et al., 2003; Shin et al., 1998). Approximately 30~50% of shells from harvested oysters was utilized and the remainder was disposed (Yoon et al., 2003; Kwon et al., 2004). Thus, recycling of waste oyster-shells has arisen as an imminent issue in the mariculture industry. As a recycling process, a lot of studies on the application of waste oyster-shells to construction materials (Yoon et al., 2003), laver farming, fertilizer (Nippon

Reuse of Waste Shells as a SO2/NOx Removal Sorbent 303

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

**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

**2.2.1 Removal of air pollutants (SO2, H2S, CO2, HCl, NOx, etc.) from the exhaust gases**  - As a desulfurization sorbents of power plants, the oyster shell is more efficient and less expensive than limestone and so its commercialization is judged to highly feasible. - The oyster shell used in the desulfurization process exhibits a high efficiency without




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

plants due to increased exchange capacity of cations used by plants.

and the cost involved in calcination should be estimated.

shell is discarded.

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

purification in a limited scope [Kim, 2007].

plant growth should be reviewed.

calcination processing.

**heavy metals** 

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 (O'Dowd et al., 1994).


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

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

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 using a fixed bed reactor.
