Effects of three kinds of organic acids on phosphorus recovery by magnesium ammonium phosphate (MAP) crystallization from synthetic swine wastewater

• The optimal pH range was 9.0–10.5 for MAP crystallization.
• Three kinds of organic acids could affect the initial P removal rate.
• High concentration of citric acid fully inhibited P removal in the whole reaction.
• Citric acid and succinic acid have effects on the shape of crystallized products.
• Complexation between organic acids and Mg2+/NH4+ caused decline of P removal.

P recovery from swine wastewater has become a great concern as a result of the high demand for P resources and its potential eutrophication effects on water ecosystems. The method of magnesium ammonium phosphate (MAP) crystallization was used to recover P from simulated swine wastewater, and the effects of three organic acids (citric acid, succinic acid and acetic acid) on P removal efficiency and rate at different pH values were investigated. The results indicated that the P removal efficiency was worst affected by citric acid in the optimal pH range of 9.0–10.5, followed by succinic acid and acetic acid, and the influencing extent of organic acids decreased with the increasing pH value. Due to the complexation between organic acid and Mg2+/NH4+, all of three organic acids could inhibit the P removal rate at the beginning of the reaction, which showed positive correlation between the inhibition effects and the concentration of organic acids. The high concentration of citric acid could completely suppress the MAP crystallization reaction. Moreover, citric acid and succinic acid brought obvious effects on the morphology of the crystallized products. The experimental results also demonstrated that MAP crystals could be obtained in the presence of different kinds and concentrations of organic acids.