Effects of organic carbon addition on microbial floc formation and water quality in closed aquaculture system

Abstract

This research examined the closed-water aquacultures by using the concept of biofloc technology. The first part of research studied the optimal condition for biofloc formation based on manipulating the substrate C:N ratio while the latter part used the information obtained from the first part to cultivate tilapia in suspension systems without any water exchange. The research also investigated the characteristics of biofloc. For the first section, tapioca starch can be substituted for glucose as means to stimulate biofloc formation. With the presence of essential elements in shrimp diets the biofloc production was more productive. The weight C:N ratio at 16:1 was able to promote the highest biofloc production and was efficient in maintaining TAN and nitrite compared to the lower C:N ratios. Pond water containing natural biofloc appeared more effective than tap water in controlling inorganic nitrogen. For the second part of this research, the daily use of C:N ratio at 16:1 was more effective in maintaining TAN and nitrite in water. Despite a significant increase of suspended solids from 30 to 1,118 mg SS/L, the effective nitrogen treatment did not proceed until a complete nitrification was established in the tanks, thereby implying that the water must be pre-acclimated to achieve the complete nitrification process. The morphology of biofloc was irregular shape containing filamentous microorganisms, rotifers, nematode, and small amount of microalgae. The proximate analysis revealed that the carbon and nitrogen contents of biofloc in the treatments were at 34.5% and 4.2%, respectively whereas the carbon and nitrogen contents in the controls were at 21.7% and 2.19%. Finally, the nitrogen balance and PCR-DGGE analysis indicated that biofloc were highly diverse and dynamics.