Nitrogen and phosphorus removal for swine wastewater using intermittent aeration batch reactor followed by ammonium crystallization process

A process for the crystallized precipitation of ammonium by adding magnesium salt and phosphate were carried out in order to remove nitrogen and phosphorus as well as to improve the C/N ratio in swine wastewater. The optimal operation conditions were obtained as follows: reaction temperature (25°C), reaction time (1 h), pH (7.5) and the molar ratio of NH4---N:PO4---P:Mg = 1.0:0.9:0.9. Under these conditions, the maximum quantity of the crystallized precipitation occurred, the removal ratio of NH4---N increased to more than 90% and the C/N ratio increased from 1.98 to more than 8, but phosphorus was not removed. On the other hand, when the molar ratio of NH4---N:PO4---P:Mg = 1.0:0.6:0.9, the ammonium and phosphorus removal ratio would be 79.32–87.45% and 40.3–88.5%, respectively. After completion of the crystallized precipitation of ammonium, an intermittent aeration process with an aeration to anaerobic time ratio of 1:1 h is used for this improved swine wastewater (T-N/BOD = 0.14, in which BOD = 8200 mg/l, T-N = 1166 mg/l, and NH4---N = 519 mg/l). The results obtained from these experiments showed that the removal ratio of T-N and NH4---N are 91 and 99%, respectively. T-P is not removed, while the removal ratio of PO4---P is 60% when 3% CaCl2 liquid is added.