Growth and nutrient removal in free and immobilized planktonic green algae isolated from pig manure

Laboratory experiments were performed to study the growth rate and phosphorus (P) and nitrogen (N) uptake of two nanoplanktonic algal species, Scenedesmus intermedius Chod. and Nannochloris sp. that were isolated from different sources of pig manure. Experiments were carried out for immobilized and free cell cultures simultaneously, with three replicates for each type of culture. Algal immobilization was prepared in calcium alginate beads. The growth rate (measured as chlorophyll increase per hour) and the P and N uptake rate (measured as P and N increase per hour) were estimated by linearization of the logistic growth and nutrient uptake curves, which allowed us to apply proper statistical comparative analyses. P and N uptake rates for S. intermedius were 0.014 and 0.012 mg P h−1 and 0.022 and 0.009 mg N h−1 for free and immobilized cells. Rates for Nannochloris sp. were 0.006 and 0.009 mg P h−1 and 0.011 and 0.006 mg N h−1 for free and immobilized cells. P and N removal rates obtained in the present study, which used species isolated from wastewater, are markedly higher than rates described in experiments that used commercial species, probably because the former species are better adapted to high nutrient concentrations. Utilizing autochthonous species for wastewater treatment may be a simple method to increase nutrient removal efficiency.