REMOVAL OF NITRATE FROM WATER BY FOAM-IMMOBILIZED PHORMIDIUM-LAMINOSUM IN BATCH AND CONTINUOUS-FLOW BIOREACTORS

Cells of the non-N2-fixing cyanobacterium Phormidium laminosum were immobilized in polyurethane (PU) foams either by absorption or by entrapment in the PU prepolymer followed by polymerisation and by adsorption onto polyvinyl (PV) foams. Although entrapment caused toxicity problems which lead to rapid death of the immobilized cells, they were immobilized successfully by adsorption onto PU or PV foams and maintained their photosynthetic electron transport activities (PS I, II, I + II) for at least 7 weeks. Changes in the morphology resulting from immobilization, as revealed by scanning electron microscopy (SEM) and low temperature-SEM, were investigated. Batch cultures and a continuous-flow packed bed photobioreactor were used to study nitrate removal from water. The effects of light intensity and CO2 concentration on bioreactor performance were studied with respect to the nitrate uptake efficiency of the system. It was concluded that P. laminosum immobilized on polymer foams is of potential value for biological nitrate removal in a continuous-flow system.