Effects of Chlorella vulgaris on phosphorus release from ferric phosphate sediment by consecutive cultivations

Iron phosphate (Fe–P) is a main phosphorus storage form, especially in phosphorus-polluted environments. The re-release of Fe–P is a problematic result during microalgal remediation. In this study, pre-incubated Chlorella vulgaris was cultured in a BG-11 culture medium with different amounts of Fe–P. The effects of Fe–P re-release on biomass, flocculation and removal of PO(4)(3−) were investigated. The results indicated that C. vulgaris can promote the dissolution and release of Fe–P when the pH is 7, and the amount of Fe–P (ΔQ) released in 200 ml water reaches 0.055–0.45 mg d(−1) under a C. vulgaris concentration of 5.6 × 10(5)–8 × 10(5) cells ml(−1). The growth of C. vulgaris was inhibited because of the flocculation behaviour of Fe(3)(+) in the release stage, which is associated with a specific growth rate of 0.3–0.4 d(−1) and a phosphorus removal rate below 30%. However, this process, in the long term, indicates a favourable transformation in which Fe–P becomes bioavailable under the action of C. vulgaris. Microalgae outbreaks may be triggered by persistent interactions between Fe–P and C. vulgaris. This study provides an important reference for the application of C. vulgaris in a Fe–P-rich environment.