Ammonia-nitrogen and orthophosphate removal by immobilized Chlorella sp. isolated from municipal wastewater for potential use in tertiary treatment

Abstract

Chlorella sp. isolated from municipal wastewater and entrapped in calcium alginate as algal sheets was employed to remove inorganic nutrients from domestic secondary effluents in parallel-plate bioreactor after starvation. The key factors affecting the nutrient removal efficiency, system stability and reuse efficiency of screens were discussed. The results show that cell density and starvation time significantly affected the nutrient uptake. A complete removal of NH₄⁺-N and PO₄^3--P was achieved within 4 h of treatment with the optimal cell density in the mixture of algal and 3 mm gel sheets after third cycle. Six cycles of wastewater treatment were accomplished in 18 days, achieving higher removal efficiency. NH₄⁺-N removal efficiency was 81% after 1.25 h and 98.81% after 4 h, while PO₄^3--P removal efficiency was 77.4% after 1.25 h and 100% after 4 h. It was confirmed that the immobilized Chlorella sp. has great potentialities in nutrient removal.

Key words: Immobilized Chlorella, starvation, wastewater treatment, nitrogen removal, phosphorus removal.