지속가능한 연안 환경 복원을 위한 패류부산물의 활용 기술에 관한 연구

Abstract

The disposal of oyster shells is a major concern in Korea, which produces more than 300,000 tons of oysters per year. Oyster shells were mainly recycled for fertilizer and feed, but their demand has been decreasing over time, and about 30% are now being accumulated and left on the coast, causing social problems. Oyster shell recycling has not received much attention due to its low economic feasibility, but as oyster shell disposal has become a serious issue, it has emerged as a value that should take precedence over economic feasibility. Studies conducted domestically and abroad have demonstrated that oyster shells are capable of adsorbing contaminants such as nutrients, hydrogen sulfide, and heavy metals. A suitable solution for improving coastal pollution could be to use oyster shells, which are environmentally friendly materials. However, research in Korean is limited to lab experiments and it is difficult to obtain field experiment data. Three technologies were proposed in this study to remediate coastal environments through laboratory and field experiments. The technology of using oyster shells as a filler for sewage treatment reduced the phosphorus concentration in sewage by more than 90%. Sulfur compounds that generate odors in sewage were also not identified after applying oyster shells. In sewage with an average phosphorus concentration of 0.8 mg-PL-1, 90% adsorption efficiency by oyster shells was maintained for about 14 days, indicating the replacement cycle of oyster shells calcined at 700 °C. Oyster shells were economical with a lower price than phosphorus coagulants in existing sewage treatment facilities. As a capping material for coastal sediments, oyster shells (calcined at 450°C) can reduce phosphate and hydrogen sulfide concentrations by 38% and 100%, respectively. Anaerobic bacteria in sediment decreased after oyster shell capping, and macrobenthos recovered quickly from the initial disturbance of capping, confirming the restoration of coastal benthic environment. Coastal sediment capping through recylcing oyster shells is considered a competitive technology because oyster shells are cheaper than other capping materials and the improvement effect is maintained for more than one year. The third technique is to attach uncalcined oyster shells to the surface of artificial reefs and use them as substrates for marine algae epiphyses. Oyster shells attached to the surface of a rectangular concrete block increased algae coverage by up to 49%. Attaching oyster shells to the surface of the reef increases the cost of manufacturing the reef, but if the number of artificial reefs is reduced due to algae growth, the economic feasibility can be increased. The above results confirmed that oyster shells are economical for improving the coastal environment. Considering ease of use, accessibility, secondary contamination, and scope of application, commercialization of oyster shell capping technology for coastal sediment remediation is considered the most suitable for mass oyster shell treatment. However, f the experimental and technical limitations that were not addressed in this study are overcome in future studies, oyster shell recycling technology is likely to become a more complete technology and contribute to commercialization.