Research on the effects of ferric salt added into aeration tank for phosphorus removal on biochemical system

In this paper, two iron salts, ferrous chloride (FeCl₂) and ferric chloride (FeCl₃), are directly added into an aeration tank for phosphorus removal, and their effects on the biochemical system are studied; the water quality parameters such as pH and alkalinity are also investigated. The extent of influence of the added iron salts on the pH and alkalinity of aerated solutions is demonstrated to be FeCl₃ > FeCl₂. When the dosage of iron ions is 20 mg/L, the decrease in pH and alkalinity caused by FeCl₃ is 0.5 and 65 mg/L, which is higher than FeCl₂ by 2% and 26%. The initial phosphorus removal effect of FeCl₂ is worse than that of FeCl₃, but after continued aeration and oxidation, the phosphorus removal effect of FeCl₂ can be improved; however, the final phosphorus removal effect is basically the same as that of FeCl₃ added directly. The results show that FeCl₂ is preferred when iron salt is added directly into the aeration tank to remove phosphorus. The proposed scheme can reduce the effect of iron salts on the alkalinity of the biochemical system on the premise of ensuring the phosphorus removal effect of the system, and is conducive to ensuring the stable operation of the biochemical system.