Microalgal culture using fish-excreted carbon dioxide and ammonia

Abstract

Microalgae were tried to grow in flasks and laboratory-scale aquaria using carbon dioxide and ammonia excreted from fish as sole sources of carbon and nitrogen. Chlorella sp. and Spirogyra sp. were selected as representatives of microalgae, and Misgurnus sp., loach was used as a representative of fish. For the solid culture of the microalgae on agar slants or agar plates, large desicators were used as culture devices. In the lower part of the desicators, tap water was filled and in which loaches were grown, whereas, in the top part, the agar slants and agar plates were placed. For the liquid culture of the microalgae, a two-stage culture method using flasks was employed. In the flasks of the first-stage culture, loaches were grown, and the microalgae were grown in the second-stage flasks. The carbon dioxide liberated from the fish respiration and the ammonia from the fish excretion are first dissolved in the water and then evaporated into the headspace to enrich the air in the solid culture device with those gasses. For the liquid culture of the microalgae, the gasses in the headspace were transferred into the second-stage flasks with compressed air. A third type of culture was performed with aquqria filled with the tap water which was devided into two horizontal zones by fine nylon nets. In the upper zone, the filamentous microalgae, Spirogyra sp. were inoculated with some loaches and in the bottom zone, only loaches were grown. Through these cultures, it was confirmed that the carbon dioxide and ammonia excreted from the fish servsd as carbon source and nitrogen source, and supported the growth of the microalgae.