Culture and nitrite uptake in immobilized Scenedesmus obliquus

Scenedesmus obliquus cells were immobilized by mixing cell suspension with sodium alginate solution (2 per cent) and adding the mixture dropwise into calcium chloride solution so that gel beads were formed. Cell growth after immobilization was studied by cell counting. Nitrite reductase activity was determined by nitrite measurements and was not affected by immobilization except that a longer lag phase was observed. This was attributed to a barrier effect of the matrix. Cell pretreatment with glycerol before immobilization in a batch reactor induced an increase in nitrite uptake which disappeared after a limited number of runs. The effect of the glycerol decreased as the number of immobilized cells increased and could be related to decreased light efficiency and reduced substrate accessibility. When buffer containing nitrite growth medium depleted in combined nitrogen was used, cellular growth occurred inside the beads up to a maximum and then the number of cells in the beads decreased.