Tadashi Hibino

Application of Granulated Coal Ash for Remediation of Coastal Sediment

본 논문에서는 석탄회 조립물을 이용한 저질개선 기술의 안전성 및 저질개선기구에 대해 논하고, 일본 카이타만 석탄회 조립물 피복구간에서의 저질개선효과에 대해 검토하였다. 석탄회 조립물의 중금속 농도 및 용출량은 일본의 환경기준을 만족하는 것으로 조사되었으며, 석탄회 조립물의 저질개선기능은 다음과 같이 요약할 수 있다. (1) 인산염 및 황화수소의 제거 (2) 산성 저질의 중화 (3) 투수성의 증가 및 이로 인한 환원상태 저질의 개선 (5) 지반강도의 증가 (6) 부착성 조류의 서식 기반. 일본 카이타만에서 실시한 현장실증실험 결과로부터 연안저질의 pH중화, 인산염 및 황화수소농도 감소 등 석탄회 조립물의 저질개선효과가 검증되었으며, 이에 따른 저서생물의 증가가 확인되었다. 석탄회 조립물을 이용한 연안저질의 개선기술이 실용화 된다면 오염저질의 정화에 소요되는 비용의 절감은 물론 산업부산물인 석탄회의 재활용에 기여할 것으로 기대된다.Abstract − This paper aims to explain the safety assessment and remediation mechanism of Granulated Coal Ash(GCA) as a material for the remediation of coastal sediments and to evaluate the improvement of the sediment inKaita Bay, where GCA was applied. The concentrations of heavy metal contained in GCA and the dissolvedamounts of heavy metal from GCA satisfied the criteria for soil and water pollution in Japan. The mechanisms onthe remediation of coastal sediments using GCA is summarized as follows; (1) removal of phosphate and hydro-gen sulfide (2) neutralization of acidic sediment (3) oxidation of reductive sediment (4) increase of water perme-ability (5) increase of soil strength (6) material for a base of seagrass. From the results obtained from the fieldexperiment carried out in Kaita Bay, it was clarified that GCA is a promizing material for remediation of coastalsediment. This remediation technology can contribute to promote waste reduction in society and to decrease cost ofcoastal sediment remediation by applying GCA in other polluted coastal areas. Keywords: Granulated Coal Ash(석탄회조립물), Remediation of Coastal Sediment(연안저질개선), HydrogenSulfide(황화수소 ), Phosphate(인산염)

INFLUENCE OF COASTAL GROUNDWATER ON BRACKISH WATER ENVIRONMENT IN A TIDAL ESTUARY

INTRODUCTION Understanding the hydrological dynamics of brackish water bodies is considered important for the effective conservation and management of the natural environment of tidal estuaries. Especially, fresh water inflows and residence times have a marked effect on the salinity within an estuary. Residence time, which refers to the mean time required to transport dissolved or suspended matter out of a water body, can be one of the limiting factors affecting phytoplankton abundance within a system (Monbet, 1992). Howarth et al. (2000) reported that a decrease in river inflows results in increased residence times and primary production in estuaries. Moreover, since the settlement and deposition of suspended matter is dependent on residence time, short residence times are considered to improve the water quality of estuarine water. A box model using salt as a conservative tracer is often applied to estimate both fresh water inflows and residence time within a system, both of which are considered important indicators of the physical condition of the estuarine environment. However, while the box model is simple in principle, the cases to which it can be applied are relatively limited, particularly in tidal estuaries because of its non-steady flow. Tidal flats along the periphery of tidal estuaries are important habitats for a variety of coastal organisms, particularly as nurseries for fish. The tidal flats of Ota River Estuary support numerous benthic fauna (16 Eucrustacea spp., 14 Pelecypoda spp. and Gastropoda spp., and 6 Polychaeta spp.) (Hibino et al., 2006). The salinity and dissolved oxygen concentration of the pore water in these areas and the particle size of the bed material has been shown to restrict the habitat preference of these species (Lalli and Persons, 1993). Submarine groundwater discharge is also important for material circulation in coastal region (Simmons, 1992; Moore, 1996; Burnett, 2003). Nonetheless, the groundwater environment of tidal flats is relatively poorly understood.

Evaluation of Granulated Coal Ash as Artificial Seabed for Eelgrass

ABSTRACT Nakashita, S.; Nakamoto, K.; Koshikawa, Y.; Kim, K.-H., and Hibino, T., 2017. Evaluation of granulated coal ash as artificial seabed for eelgrass. In: Lee, J.L.; Griffiths, T.; Lotan, A.; Suh, K.-S., and Lee, J. (eds.), The 2nd International Water Safety Symposium. Journal of Coastal Research, Special Issue No. 79, pp. 40–44. Coconut Creek (Florida), ISSN 0749-0208. Granulated coal ash (GCA) is a by-product of coal-fired thermoelectric power stations. In this study, GCA was used to create a functional artificial seabed for eelgrass. Moreover, the capability of GCA for the growth of eelgrass in an indoor experiment was examined to elucidate the ability of eelgrass to establish itself and grow in a GCA artificial seabed created in an actual marine environment. The eelgrass in the GCA artificial seabed branched and adapted similar to that on sandy ground. A stable eelgrass community was established in one year in an actual marine environment. Furthermore, five years after transplantation, the eelgrass community was maintained. For the GCA artificial seabed, the oxidation–reduction potential of the bottom sediments was approximately 100 mV higher than that of the surrounding ground, and the amount of sulfide decreased to approximately one third of that of the surrounding ground. Even five years after construction, a stable environment was preserved. Therefore, it is concluded that GCA is an effective material for an eelgrass seabed.

Remediation of Muddy Tidal Flat using Porous Pile

Field experiment were carried out to investigate the formation of ground water flow and remediation of muddy tidal flat by installation of porous pile at the tidal flat of brackish river located in Hiroshima City, Japan. After the installation of porous pile, the concentrations of Dissolved Oxygen (DO) in the interstitial water in the porous pile increased with maximum concentration of 4 mg/L due to a formation of groundwater flow. It was observed that a increase in Oxidation Reduction Potential (ORP) and a decrease in Ignition Loss (IL) in the porous pile site and these must be caused by the increase of dissolved oxygen in the interstitial water. From these results obtained above, it is concluded that the porous pile is an effective technology for remediation of muddy tidal flats.