Nutrient uptake and growth of immobilized filamentous microalgae Stigeoclonium nanum (Dillwyn) Kützing 1849 for improvement of water quality

In aquaculture practices, a large amount of water has to be exchanged frequently in order to maintain good water quality. This procedure contributes to the eutrophication of aquatic environment due to flushing of nutrient-enriched waters from aquaculture facilities. Furthermore, the process of frequent water exchange will eventually result in lack of good water supply which can also increase the risk of diseases in the hatchery. To overcome eutrophication and the risk of diseases, an alternative eco-friendly method was investigated to decrease harmful compounds especially ammonia and nitrite by using microalgae. In this study, filamentous green microalgae Stigeoclonium nanum was used. The first objective of this project was to study growth of the filamentous microalgae (S. nanum) immobilized in alginate beads and in free suspension condition. Four experimental treatments, control 1 (no algae and no beads), control 2 (beads with free algae), algae in free suspension and beads with algae were tested. The parameters that were examined included S. nanum growth in terms of chlorophyll-a content, and ammonium loading for the microalgae culture. The ammonia loading is ammonia which was added up during experiment when it has zero reading. From the study, significantly higher (p < 0.05) chlorophyll-a content was observed in alginate beads (5.27 ± 0.63 mg/l) on the final day of the experiment than the microalgae cultured in normal suspension culture (0.62 ± 0.20 mg/l). Significantly higher (p < 0.05) total ammonium loading was also observed in the culture of immobilized microalgae. The second objective of the experiment was to measure the uptake of the ammonia-N (NH4-N) and nitrate-N (NO3-N) by immobilized filamentous microalgae. Five culture media with different concentrations of NO3-N and NH4-N were tested in this experiment, treatment A was Bold’s Basal Medium (BBM), treatment B was zero concentration of NO3-N and NH4-N (control), treatment C was zero concentration of NO3-N with 10 mgL -1 concentration of NH4-N, treatment D was 10 mgL -1 of NO3-N with zero concentration NH4-N, and treatment E was 10 mgL -1 of NO3-N with 10 mgL -1 of NH4-N.. The parameter examined was S. nanum uptake of the NH4-N and NO3-N. This study illustrated that NH4-N was preferred than NO3-N as nitrogen source by the immobilized S. nanum.

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