In order to construct a closed ecological recirculating aquaculture system (CERAS), a fish-rearing closed tank was developed as the first step. The system consisted of a 55-liter closed tank with two membrane modules for gas exchange, two biofilters, a circulatory pump, and sensors for monitoring dissolved oxygen (DO) and pH. Ten tilapia, Oreochromis niloticus, approximately 100g weighing (total length 15cm) each and fed a commercial diet, were cultured in the closed tank for 6-17 days at 28°C. During the experimental term, the water qualities, such as pH, DO, NH₄, NO₂^-N, NO₃^-N, were monitored. The ammonia excretion from tilapia was 14.4mg/kg/h. Using this value, the nitrification capacity of the biofilter was calculated. The biofilter nitrified 62.5% of ammonia. In this closed tank system, 0.86-1.6% of the daily feeding rate, 40-80% of the standard feeding rate, was sufficient for normal fish growth.

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The closed ecology experiment facilities (CEEF) are composed of the closed plant experiment facilities (CPEF) and the closed geo-hydrosphere experiment facilities (CGEF). CGEF consists of an animal breeding/habitation module and geo-hydrosphere experiment facilities. The construction of CPEF and the establishment of the devices of CPEF have been completed, and at present, partial test operations are now in progress. Reports for these tests are now available. The animal breeding/habitation module of the closed geo-hydrosphere experiment facilities (CGEF) were established in 1996. This report is concerned with the modeling of CPEF with the cultivation of 7 different crops, each crop with differing stages of cultivation. This report will also detail the results of the analysis of the material circulation of this model, which are based on currently available device data.

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The closed plant experiment facilities (CPEF) and closed geo-hydrosphere experiment facilities (CGEF) have a cooperative function which exchanges substances such as gas and water in CEEF. Initially, CPEF and CGEF are operated individually. However, if the material balance and individual devices' performances are satisfactory, substances are exchanged to accommodate any short-falls or excesses between CPEF and CGEF. This report demonstrates the modeling of CGEF and the results of the analysis of the substance exchanges as part of the cooperative operation between CPEF and CGEF.

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We have investigated several microalgal culturing systems for CO₂ elimination and O₂ regeneration in closed air. We constructed an experimental microalgal culturing system and studied the effects of temperature, pH, O₂ concentration in a supply gas using a reactor aerated with low CO₂ concentration (1000ppm) on the cell growth of Chlorella sorokiniana ATCC22521 and the CO₂ elimination rate in a reaction vessel on batch culture. We also studied repeated batch culture under a low concentration of CO₂. Our study suggested that the CO₂ concentration in the supply gas limitted the algal system performance.
We tested the system under a high concentration of CO₂ (5%) as an optimum growth condition of Chlorella sorokiniana ATCC22521 cells on batch culture and repeated batch culture as a first step of continuous culture.
As a result, we confirmed that the maximum CO₂ elimination rate under a high concentration of CO₂ was about 5 times higher and the maximum chlorophyll synthesis was about 2 times higher than those values under the low concentration of CO₂. The gas exchange efficiency under the high concentration of CO₂ was little affected by bacterial contamination in comparison with being under a low concentration of CO₂. The maximum O₂ evolution rate and CO₂ elimination rate showed little difference among each tested concentration of nitrogen source but the nitrogen source concentration in the culture medium was one of the most important factors to maintain the performance of O₂ evolution and CO₂ elimination in the system.

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