Nitrate and Phosphate Removal by Co-immobilized Chlorella pyrenoidosa and Activated Sludge at Different pH Values

sludge was studied. The results showed that the co-immobilized system was adaptable to the environment; the micro-algae reproduced rapidly inside a PVA gel carrier under pH ranging from 5.0 to 10.0. Phosphate removal efficiency of the co-immobilized system was distinctly affected by pH but nitrate removal efficiency was not affected very much. The co-immobilized system had a higher removal efficiency in the water when close to neutral. Under suitable circumstances, the removal efficiency of nitrate reached 80% in all four experimental periods; meanwhile, the highest removal efficiency of phosphate was 88% but decreased to 56% from the first period to the fourth period in the experiment.