Bulletin of the Society of Sea Water Science, Japan
Online ISSN : 2185-9213
Print ISSN : 0369-4550
ISSN-L : 0369-4550
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Volume 73, Issue 1
Displaying 1-9 of 9 articles from this issue
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Preface
Special Issue : “A Study of the Seawater of West Japan (8)”
Introduction
Review
  • Principle and Recent Technological Trend of Power Generation Using Salinity Gradient Energy
    Mitsuru HIGA
    2019 Volume 73 Issue 1 Pages 3-8
    Published: 2019
    Released on J-STAGE: October 01, 2020
    DOIhttps://doi.org/10.11457/swsj.73.1_3
    JOURNAL FREE ACCESS
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    One of the renewable energies is salinity gradient power which converts salinity gradient energy existing between salt water such as sea water and fresh water such as river water into electricity. Mixing 1 m3 of seawater with 1 m3 of fresh water theoretically generates 1.7 MJ of energy, which is equivalent to about 500 Wh. Salinity gradient power is expected as a base load power source derived from renewable energy with low environmental impact, high equipment utilization rate, and small footprint. There are two types of salinity gradient power using separation membranes: Pressure Retarded Osmosis （PRO） using semipermeable membranes, turbine and generators, and Reverse ElectroDialysis （RED） using ion exchange membranes. There were reports that in the case of using seawater, RED will be superior to PRO, and in the case of high concentration salt solution such as concentrated sea water etc. PRO will be better than RED. World's first RED power generation pilot plant was installed in Afsluitdiik, Netherlands. Recently, SWRO-PRO hybrid plant was built in Busan, Korea. In the future, the improvement in the performance of the forward osmosis membrane and ion exchange membrane will give practical applications of the two technologies.
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Commentary
Note
  • Removing Sulfate Ions from ED Brine by Reactive Crystallization of Calcium Sulfate with Adding Calcium Chloride
    Taichi KIMURA, Koji MASAOKA, Hayato MINEO, Yoshinari WADA, Toshihiko H ...
    2019 Volume 73 Issue 1 Pages 24-29
    Published: 2019
    Released on J-STAGE: October 01, 2020
    DOIhttps://doi.org/10.11457/swsj.73.1_24
    JOURNAL FREE ACCESS
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    In Japan, during the salt manufacturing process, electrodialysis （ED） brine is obtained by concentrating seawater via electrodialysis by using ion-exchange membranes. A method that enables the elimination of SO42－ from the ED brine by the reactive crystallization of calcium sulfate （CaSO4） has been developed to utilize ED brine as a raw material in the electrolytic alkali industry and improve the efficiency of the salt manufacturing process by minimizing scale formation during evaporative concentration and crystallization. Powdered calcium chloride （CaCl2） was added to the simulated ED brine containing inorganic ions （Na＋, K＋, Ca2＋, Mg2＋, Cl－, SO42－, and Br－） in concentrations identical to those in the actual ED brine, and CaSO4 was crystallized for 18 days at a reaction temperature of 303 K. The concentration of added CaCl2 （（CCaCl2）add） was used as a variable operating parameter, and the effects of CaCl2 addition on the reduction in SO42－ ion concentration in the simulated ED brine were investigated. When （CCaCl2）add was higher than 0.297 mol/L, a decrease in the concentration of SO42－ ions （CSO4） was induced by the crystallization of CaSO4 with increasing reaction time, and CSO4 became approximately constant six days after CaCl2 addition. After six days, CSO4 decreased with increasing （CCaCl2）add; however, the decreasing trend in CSO4 with increasing （CCaCl2）add was less significant when （CCaCl2）add was higher than 1.0 mol/L. When （CCaCl2）add was set to 1.0 mol/L, CSO4 can be reduced to 0.002 mol/L. Thus, the addition of powdered CaCl2 can be considered effective for reducing the SO42－ ion concentration in the ED brine produced during salt production in Japan.
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  • Promotion of Cyanobacteria Growth Induced by Fine Bubble Injection
    Sawako KATOH, Yoshinari WADA, Mitsunori KATAYAMA, Chikako NORO, Kazuak ...
    2019 Volume 73 Issue 1 Pages 30-34
    Published: 2019
    Released on J-STAGE: October 01, 2020
    DOIhttps://doi.org/10.11457/swsj.73.1_30
    JOURNAL FREE ACCESS
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    In this study, a cultivation technique enabling growth promotion of cyanobacteria with low efficiency CO2 absorption and conversion to organic compounds was developed utilizing the gas-liquid interfaces surrounding fine air bubbles as new reaction fields for photosynthesis. Cyanobacteria CO2 absorption efficiency is increased in the regions near the fine bubble surfaces because of the accelerated CO2 mass transfer caused by minimizing the bubble diameter, as well as cyanobacteria accumulation due to the negative charge on the fine bubble surface; hence, the rate of photosynthesis is increased and cyanobacteria growth is promoted. Fine air bubbles with an average bubble diameter （dbbl） of 80 μm were continuously supplied to culture medium containing cyanobacteria in a semi-batch photobioreactor equipped with a self-supporting bubble generator, a fluorescent lamp, and a reaction vessel and the cyanobacteria were grown at a reaction temperature of 30 ℃. The light intensity was changed by the number of fluorescent lamps located inside and outside of the reaction vessel. Additionally, the dbbl was varied along a range of 40 to 6,000 μm at a constant light intensity. Consequently, when the light intensity range was 37 - 527 μmol·m－2·s－1 at a dbbl of 80 μm, the specific growth rate of the cyanobacteria （rsg） showed a maximum value at a light intensity of 365 μmol·m－2·s－1. Furthermore, at a light intensity of 365 μmol·m－2·s－1, the rsg noticeably increased with a decrease in dbbl and the rsg at a dbbl of 40 μm was approximately 2.5-fold greater than that at 1,500 μm. These results indicate that fine bubble injection promoted cyanobacteria growth in a semi-batch photobioreactor under CO2-limited conditions.
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