Nitrate and phosphate removal by co-immobilized Chlorella pyrenoidosa and activated sludge at different pH value

Abstract

A new immobilization method, the simplifying modified polyvinyl alcohol (PVA)-sulfate method, has been evaluated. The influence of pH value on nitrate and phosphate removal by co-immobilized Chlorella pyrenoidosa and activated 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.