A novel Fe(II)-Ca synergistic phosphorus removal process: process optimization and phosphorus recovery.

Phosphorus removal from wastewater is an important means to control eutrophication and to recover phosphorus from wastewater. In this study, a novel Fe(II)-Ca synergistic phosphorus removal process is developed using the complex of ferrous and calcium salts. The results showed that ferrous and calcium had an antagonistic effect at Fe(II)/Ca molar ratio of lower than 1:4, but a synergistic effect at Fe(II)/Ca molar ratio of higher than 1:4, with the strongest synergistic effect at Fe(II)/Ca molar ratio of 7:3. The optimal parameters of this novel process were as follows: Fe(II)/Ca = 3:1, ferrous-calcium complex/phosphorous (M/P) ≥ 1.5:1, pH = 7.0-8.0, and fast mixing speed (FMS) = 100-150 rpm. The cost of phosphorus removal agents was US$1.024 (kg P)-1, reduced by 30.39% compared with that of the traditional phosphorus removal process. The phosphorus content (by P2O5) in the precipitate produced in the new process was 32.70%, which had a high recycling value.