Cu(II) removal by Nostoc muscorum and its effect on biomass growth and nitrate uptake: A photobioreactor study

•Complete removal of Cu(II) by N. muscorum was achieved at all initial concentration.•A high initial Cu(II) concentration inhibited the biomass growth and nitrate uptake.•Han-Levenspiel model best described the nitrate uptake in presence of Cu(II).•Critical Cu(II) concentration for nitrate uptake is 32.5 mg L−1.

This study investigated the Cu(II) removal by Nostoc muscorum, a cyanobacterium isolated from a toxic metal polluted site in Meghalaya, using a batch photobioreactor with an aim to elucidate the removal mechanism and its effect on nitrate uptake by the cyanobacterium. Experiments were carried out using a batch photobioreactor by varying the initial Cu(II) concentration in the range of 5-30 mg L−1. Results obtained in this study showed that a maximum of 5.628 ± 0.05 g L−1 of biomass concentration could be obtained in the absence of Cu(II), whereas this value of biomass reduces to 4.3 ± 0.0057 g L−1 in presence of 5 mg L−1 of initial Cu(II) concentration, which further reduces to 2.51 ± 0.01 g L−1 for an initial Cu(II) concentration of 30 mg L−1. Besides, an increase in the initial Cu(II) concentration delayed the uptake of nitrate by the cyanobacterium. However, complete removal of Cu(II) was observed for all the four different initial Cu(II) concentration. The estimated value of nitrate uptake rate in the absence of Cu(II) was found to be 0.115 mg L−1 d−1, which was reduced to 0.029 mg L−1 d−1 due to 30 mg L−1 initial Cu(II) concentration in the medium. The experimental nitrate uptake rate values were fitted to three unstructured kinetic models reported in the literature for estimating the biokinetic constants. Among the three models, Han-levenspiel and Andrew models fitted the experimental data closely with a determination coefficient (R2) value of 0.942 and 0.921, respectively. The critical Cu(II) concentration obtained as per the Han-levenspiel model was found to be 0.0325 g L−1.