Satoshi Asaoka

Removal of hydrogen sulfide using crushed oyster shell from pore water to remediate organically enriched coastal marine sediments.

Hydrogen sulfide is highly toxic and fatal to benthic organisms as well as causing depletion of dissolved oxygen and generating blue tide in eutrophic coastal seas. The purposes of this study are to reveal adsorption characteristics of hydrogen sulfide onto crushed oyster shell, and to evaluate removal efficiency of hydrogen sulfide from pore water in organically enriched sediments using container experiment in order to develop a coastal sediment amendment. The crushed oyster shell was mainly composed of CaCO(3) with calcite and CaO crystal phase. The batch experiment showed removal kinetics of hydrogen sulfide can be expressed as the first order equation and Langmuir plot fitted well in describing the adsorption behavior with the adsorption maximum at 12 mg-S g(-1). The container experiments suggested the oyster shell adsorbs hydrogen sulfide in pore water effectively and reduces oxygen consumption in the overlying water. Furthermore, oxidation-reduction potential of the sediment was higher with addition of crushed oyster shell than the control without oyster shell. Thus, it is concluded that crushed oyster shell can be an effective amendment to remediate organically enriched sediments in eutrophic coastal seas.

Combined adsorption and oxidation mechanisms of hydrogen sulfide on granulated coal ash

Hydrogen sulfide is highly toxic to benthic organisms and may cause blue tide with depletion of dissolved oxygen in water column due to its oxidation. The purpose of this study is to reveal the combined adsorption and oxidation mechanisms of hydrogen sulfide on granulated coal ash that is a byproduct from coal electric power stations to apply the material as an adsorbent for hydrogen sulfide in natural fields. Sulfur species were identified in both liquid and solid phases to discuss removal mechanisms of the hydrogen sulfide with the granulated coal ash. Batch experiments revealed that hydrogen sulfide decreased significantly by addition of the granulated coal ash and simultaneously the sulfate ion concentration increased. X-ray absorption fine structure analyses showed hydrogen sulfide was adsorbed onto the granulated coal ash and successively oxidized by manganese oxide (III) contained in the material. The oxidation reaction of hydrogen sulfide was coupling with reduction of manganese oxide. On the other hand, iron containing in the granulated coal ash was not involved in hydrogen sulfide oxidation, because the major species of iron in the granulated coal ash was ferrous iron that is not easily reduced by hydrogen sulfide.

Remediation of coastal marine sediments using granulated coal ash

It is very important to reduce phosphorus flux from sediment as well as cutting down terrigenous loads in order to control eutrophication in semi-enclosed coastal seas. Hydrogen sulfide is also a noxious substance which is highly toxic and fatal to benthic organisms. The purpose of this study is to evaluate remediation efficiency of organically enriched sediments using granulated coal ash (GCA) in terms of reducing benthic phosphorus flux and hydrogen sulfide. A flow-through experimental system was used to simulate the semi-enclosed water bodies. The application of GCA decreased the concentration of PO4(3-) in the pore water effectively, and reduced phosphate releasing flux from the sediment into overlying water by 37-44% compared to the control. The hydrogen sulfide in the pore water was also decreased by 77-100%, due to adsorption onto the GCA and deactivation of sulfate-reducing bacteria due to increasing pH. Thus, GCA is a promising recycled material for reducing phosphate releasing flux from organically enriched sediment to alleviate eutrophication as well as reduce the concentration of hydrogen sulfide in pore water.

Characteristics of phosphate adsorption onto granulated coal ash in seawater

The deterioration of sediments is a serious environmental problem. Controlling nutrient release fluxes from sediments is important to alleviating eutrophication and to reducing terrigenous nutrient loads. The purpose of this study was to evaluate the phosphate removal performance of granulated coal ash (GCA) from seawater, which is produced from coal thermal electric power generation. Batch experiments were carried out to investigate the removal kinetics of phosphate from seawater under both oxic and anoxic conditions. Phosphate was removed well from seawater under both oxic and anoxic conditions. The adsorption isotherm for phosphate revealed that GCA could remove phosphate effectively from seawater above a concentration of 1.7micromolL(-1). GCA can reduce the concentration of phosphate in seawater effectively under anoxic conditions where iron type adsorbents cannot be applied. Therefore, GCA could potentially be used to adsorb phosphate in the organically-enriched sediment, which generally occurs under highly reductive conditions.

Remediation of muddy tidal flat sediments using hot air-dried crushed oyster shells

In order to prove that hot air-dried crushed oyster shells (HACOS) are effective in reducing hydrogen sulfide in muddy tidal flat sediments and increasing the biomass, field experiments were carried out. The concentration of hydrogen sulfide in the interstitial water, which was 16 mg SL(-1) before the application of HACOS, decreased sharply and maintained almost zero in the experimental sites (HACOS application sites) for one year, whereas it was remained at ca. 5 mg SL(-1) in the control sites. The number of macrobenthos individuals increased to 2-4.5 times higher than that in the control site. Using a simple numerical model, the effective periods for suppression of hydrogen sulfide were estimated to be 3.2-7.6 and 6.4-15.2 years for the experimental sites with 4 and 8 tons per 10 × 10 × 0.2m area, respectively. From these results, it is concluded that HACOS is an effective material to remediate muddy tidal flats.

Blast furnace slag can effectively remediate coastal marine sediments affected by organic enrichment

There is an urgent need to control nutrient release fluxes from organically-enriched sediments into overlying waters to alleviate the effects of eutrophication. This study aims to characterize blast furnace slag (BFS) and evaluate its remediation performance on organically-enriched sediments in terms of suppressing nutrient fluxes and reducing acid volatile sulfide. BFS was mainly composed of inorganic substances such as CaO, SiO(2), Al(2)O(3) and MgO in amorphous crystal phase. Container experiments showed that the phosphate concentration in the overlying water, its releasing flux from sediment and AVS of the sediment decreased by 17-23%, 39% and 16% compared to the control without BFS, respectively. The loss on ignition was significantly decreased by 3.6-11% compared to the control. Thus, the application of BFS to organically-enriched sediment has a suppressive role on organic matter, AVS concentration and phosphate releasing flux from sediments and therefore, is a good candidate as an effective environmental remediation agent.

Growth and uptake kinetics of phosphate by benthic microalga Nitzschia sp. isolated from Hiroshima Bay, Japan

In the present study, we experimentally investigated the phosphate uptake kinetics of benthic microalga Nitzschia sp. isolated from Hiroshima Bay, Japan. The maximum uptake rate (ρmax) obtained by short‐term experiments was 6.84u2003pmolu2003cell−1u2003h−1 for phosphate. The half‐saturation constant for uptake (KS) was 61.2u2003µmol cell−1u2003h−1. Both the ρmax and Ks of this species were extremely high, suggesting that Nitzschia sp. is adapted to benthic environments, where nutrient concentrations are much higher than in the water column. The specific maximum growth rate (µmax) and minimum cell quota (Q0) for the P‐limited condition, obtained by a semi‐continuous growth experiment, were 0.48u2003day−1 and 0.045u2003pmolu2003cell−1, respectively. It is concluded that Nitzschia sp. could be a ‘storage strategist’ species, meaning it adapts so as to minimize the influence of fluctuations in phosphate conditions resulting from the change in redox conditions of sediment due to bioturbation.

Phosphorus mass balance in a highly eutrophic semi-enclosed inlet near a big metropolis: A small inlet can contribute towards particulate organic matter production

Terrigenous loading into enclosed water bodies has been blamed for eutrophic conditions marked by massive algal growth and subsequent hypoxia due to decomposition of dead algal cells. This study aims to describe the eutrophication and hypoxia processes in a semi-enclosed water body lying near a big metropolis. Phosphorus mass balance in a small inlet, Ohko Inlet, located at the head of Hiroshima Bay, Japan, was quantified using a numerical model. Dissolved inorganic phosphorous inflow from Kaita Bay next to the inlet was five times higher than that from terrigenous load, which may cause an enhancement of primary production. Therefore, it was concluded that not only the reduction of material load from the land and the suppression of benthic flux are needed, but also reducing the inflow of high phosphorus and oxygen depleted water from Kaita Bay will form a collective alternative measure to remediate the environmental condition of the inlet.