Use of experimental planning to evaluate the effect of the C/N and N/P ratio on the growth kinetics of a cyanobacterium

Abstract

Aphanothece microscopica Nägeli is a cyanobacterium with the ability to grow in effluents originated from industrial activities by exploiting its auxiliary mechanisms such as respiration to remove nutrients from the effluents and to generate bioproducts with aggregated values. The present work aims to contribute to the optimization of the C / N and N / P ratio in the dairy effluent, allowing the evaluation of the effect of these elements on the growth kinetics of Aphanothece microscopica Nägeli. The cultivation of the cyanobacteria were conducted in the dairy effluent in a heterotrophic bioreactor under initial cell concentration conditions of 200 mg L-1, initial pH 7.6, temperature of 30 ° C, continuous aeration and absence of light. A factorial experimental design (3²) was used with the following factors: C/N (20, 40, and 60) and N/P (5, 10, 15). The C/N and N/P ratios were adjusted based on the previously determined COD/N-NTK and N-NTK / P-PO4-3 ratios in the effluent. The C/N ratio was adjusted with glucose and N/P with disodium phosphate. The cultivation of Aphanothece in the effluent with the C/N 20 and N/P 10 ratios obtained the best kinetic values with a maximum cell concentration of 1045 mg. L-1, maximum specific growth velocity of 0.250 h^-1, generation time of 2.77 h and batch time to reach the maximum cell concentration of 6 h.