In this study, we used the minute gas-liquid interfaces around CO2/NH3 micro-bubbles as new reaction fields where the crystal nucleation progresses and developed a crystallization technique to control the crystal structure (polymorph) of calcium carbonate (CaCO3). At the minute gas-liquid interfaces, numerous local supersaturation regions are generated due to minimizing bubble size and mixing of NH3 gas with CO2 gas; hence, the polymorph change of CaCO3 is expected to occur. CaCO3 was crystallized at 298K by a semi-batch type reaction in which CO2/NH3/N2 bubbles were continuously supplied to an aqueous Ca(NO3)2 solution using a self-supporting bubble generator. The solution pH during crystallization was maintained constant at 9.7 by adding HNO3 and NH4OH solution. The average bubble size (dbbl) was varied within the range of 40 – 1000μm by controlling the N2 flow rate, and the molar ratio of CO2/NH3 (αCO2/NH3) was set at a specified value of 0.20 – 1.00 at a constant CO2 flow rate. By varying dbbl and αCO2/NH3, the effects of minimizing bubble size and mixing of NH3 with CO2 on the polymorphism of CaCO3 were examined. Consequently, during reactive crystallization of CaCO3 using CO2/NH3 micro-bubbles, the crystallized polymorph was changed from vaterite to aragonite when dbbl was decreased, and the production of aragonite with minimizing bubble size was accelerated markedly with a decrease in αCO2/NH3.
Aquaculture has developed in the enclosed bays and coves along Japanese coast since the 1970s, and the total catch reached approximately 1.2 million tons per year by 2007. However, many fish farms are suffering from a deterioration in water quality. To keep DO conditions of the farms is one of the most serious tasks for sustainable development. Two different measures have been adopted recently for the management of water quality of the farms. One is to move the farms to offshore areas in the open seas to increase water exchange, and another is to develop a new technique to increase DO supply to the water of the present farms in the enclosed coastal seas with microbubble injectors. In this review, I focus on recent achievements of microbubble techniques for aquaculture, and refer to the sustainable development of fish farming in the enclosed coastal seas with this technique.
This paper describes the examination results for clarifying the first maturation and season of hanging cultured iwagaki oyster Crassostrea nippona in Uragou Bay, Oki, Shimane, Japan. 0-year old oysters were collected monthly from May to December in 1995, and shell height, soft tissue weight, gonad index and standard histological analysis were measured to observe the stages of gametogenic development and spawning. From the results, it was clear that the season for starting early gametogenic development of 0-year-old oysters was later than that of fishery size oysters in published reports. Most of the oysters were mature in August, with a mean shell length of 50mm. It was estimated that the spawning peak occurred between August and September, coinciding with a decrease in water temperature from the highest temperature, which is the same season for fishery size oysters