Integrated Aquaculture System of Fish, Microalga, Zooplankton and Aquatic plants

Abstract

This work was designed to give engineering detail for the design of a recirculating aquaculture system where wastes from one part are being consumed as feed for other organisms in the whole concocted ecosystem (Integrated Multi-Trophic Recirculating Aquaculture System, IMRAS). The experiments were separated into 2 main parts. Part I (Algal nutrition adjustment) aimed to study the effect of several environmental parameters (light intensity, temperature, and aeration rate) on the accumulation of nutritional components and lutein production in a green microalgae Chlorella sp. It was proven in this work that the biochemical composition of Chlorella sp. could be manipulated through the control of environmental conditions during the cultivation. Six simple 2L bubble column photobioreactors installed in a well controlled culture chamber were employed as a model system where temperature, light intensity, and aeration rate (usg) could be controlled in the range from 30-40ºC (± 0.5ºC), 10-30 kLux (± 0.1 kLux), and 0.5-1.5 cm/s (± 0.05 cm/s), respectively. Lipid and protein productivity were the most abundant at 35°C, 10 kLux and 1 cm/s, whereas carbohydrate productivity was found to be maximized at 30°C, 30 kLux and 0.5 cm/s. In addition, Chlorella sp. could also generate strong antioxidizing agents like lutein which was found to be mostly produced at 35°C, 10 kLux and 1 cm/s. Part II (Outdoor cultivation) aimed to study outdoor cultivation of integrated multi-trophic recirculating aquaculture system, where Chlorella sp. and aquatic plants tanks acted as a nitrogen conversion unit. In this work, three densities of the sex-reversed male Nile tilapia, Oreochromis niloticus (20, 25, 50 fish/m3) were cultivated in IMRAS that involved the ecological relationship between several living organisms, i.e. phytoplankton, zooplankton, and aquatic plants. The results indicated that, by providing proper interdependency between various species of living organisms, the concentrations of ammonia, nitrite, nitrate, and phosphate in the system were controlled below dangerous level for Nile tilapia throughout the cultivation period. The highest wet weight productivity of Nile tilapia of 11±1 kg/m3 was achieved at the initial fish density of 50 fish/m3. The aquatic plants in the treatment tank could effectively uptake the unwanted nitrogen (N) and phosphorus (P) compounds with the highest removal efficiencies of 9.52 and 11.4%, respectively. The uptake rates of nitrogen and phosphorus by aquatic plants could be ordered from high to low as: Egeria densa > Ceratophyllum demersum > Vallisneria spiralis and Vallisneria Americana > Hygrophila difformis. The remaining N (39.67%) was further degraded through denitrification process whereas the remaining P (54.46%) could well precipitate in the soil sediment in the treatment tank.