In Situ Photosynthesis Of Immobilized Chlorella Sorokiniana GXNN01and Removal Of Nitrogen And Phosphorus From Wastewater

Considerable attention has focused on the use of microalgae for the treatment of wastewater. However, many practical application problems associated with this treatment method remain, particularly concerning secondary pollution by cells in treated effluent and the high cost of the treatment process. We captured Chlorella sorokiniana GXNN01, that had been isolated from a wastewater treatment pond, in calcium alginate as algal beads and used these to measure growth and photosynthetic activity in immobilized, and free-living, cells. We also investigated nutrient uptake (of N and P) by Chlorella sorokiniana GXNN01from synthetic wastewater under autotrophic (AA), heterotrophic (HA), mixotrophic (MA) and micro-aerobic (MNA) conditions. Results indicated that immobilized and free-living cells both grow well in micro-anaerobic conditions. By the end of the experiment, the biomass, growth rates and photosynthetic activity were noted to be higher in immobilized cells than in free-living cells. Immobilized cells also had a slightly higher rate of removal of ammonium (43.59%and21.84%), under HA and AA conditions, from synthetic wastewater, than was the case for free-living cells (38.57%and14.35%). In the case of phosphate removal, however, the rates in immobilized cells (88.65%,87.49%and84.84%) were significantly higher than those measured in free-living cells (42.27%,20.21%and53.52%) under MA, HA and MNA conditions. Because the pH values of immobilized cell flasks were>8.0, precipitation of phosphate as calcium phosphate results in leakage of cells from alginate beads. We therefore suggest that other methods should be used to initially remove phosphorus from wastewater, after which immobilized cells can be used to remove nutrients from wastewaters. We therefore found that immobilized Chlorella sorokiniana GXNN01is a suitable species for use in wastewater treatment.