COST OF NUTRIENTS IN DIFFERENT METHODS OF FERTILIZATION FOR AEROBIC MICROBIAL FLOC PRODUCTION IN INDOOR TANKS
The aim of this study was to evaluate the effect of two methodologies of fertilization on the volume and characteristics of floc. Nine aquarium glass tanks (75 litres each) were divided into three treatments. The treatment 1 followed the fertilization regimes of including nitrogen fertilizers, treatment 2 was studied with the inclusion of both nitrogen and phosphorus fertilizers and treatment 3 was the control where the conventional method of fertilization was adopted. In treatment 1 & 2, the tanks received daily molasses fertilization throughout the entire rearing period. In control, molasses was used only initial fertilization was done. Distillery spentwash obtained as effluent from sugarcane industries were used as the carbon source. The tanks were operated with no water exchange and the total suspended solids concentration were kept between 300 and 400 mg L−1 .The sludge produced at harvest were quantified and their characteristics were determined. The production of TSS in the treatment 1 was higher than in the treatment 2 (P < 0.05). The analysis of the sludge revealed a high amount of volatile solids in both treatments, between 636 and 702 g kg−1. The BOD: TSS ratio was also low in both treatments, but the treatment 2 showed lower values (11.3 ± 0.6%) than the treatment 1 (15.9 ± 0.0%) (P < 0.05). Both fertilization strategies were able to modify the characteristics of sludge produced during cultivation. Moreover, the nitrogen and phosphorus content in treatment 2 showed a increased floc volume (15.42±0.2ml) within 7 days and it was much easier to maintain the floc in both the treatments. The TPC was significantly different in treatment 2 (P < 0.05) indicates the growth of heterotrophic bacteria. The study concludes that cost of application of nitrogen and phosphorus fertilizers in treatment 2 was comparatively higher and increases the floc volume within seven days.