Ferrous Cooperative Dephosphorization In Denitrifying Phosphorous Removal Process

Water pollution of nitrogen and phosphorus is increasingly serious. The key to solve the problem is the advanced removal of nitrogen and phosphorus in wastewater treatment. The wastewater discharging standards are becoming stricter. It has gradually become a tendency that the effluent discharging standards should achieve to the surface water class IV and class III standard quality index. In southern China, due to insufficient carbon source in sewage, most traditional wastewater treatment technology has weakness of insufficient in nitrogen and phosphorus removal. However, denitrifying phosphorus removal process has significant advantages in treating low carbon source sewage. And the effluent can reach the first grade A standard. This study with the goal of total phosphorus of effluent from denitrifying phosphorus removal process meeting the surface water class III standard?0.2 mg/L?, in the premise without any increase of process unit, research the chemical cooperative phosphorus removal technology based on ferrous salt, explore high phosphorus removal technology solutions.First of all, we optimized the conditions of ferrous chemical cooperative phosphorus removal in the denitrifying phosphorus removal sludge system through beaker experiment. Under the condition of the same dosing quantity, when compared the different dosing position of phosphorus removal effect, the results show that dosing Fe²⁺ at the beginning of the anaerobic and anoxic have better efficiency of phosphorus removal. Then, we investigated the impact of different concentrations of Fe²⁺ on the system at two dosing positions respectively. The results show that in the short term, adding ferrous does not affect the decontamination effect, sludge properties and sludge activity of the system.Secondly, based on small experimental optimization conditions, we studied the influence of dosing ferrous to denitrifying phosphorus removal sludge system running effect, and compared with the aerobic sludge system using the SBR reactor to carry out the long-term dynamic experiment. The results show that the average concentration of phosphorus of reactor R0(without adding the Fe²⁺) is 1.26 mg/L, however both of the phosphorus of the effluent of reactor R1(dosing Fe²⁺ at the beginning of anaerobic) and the reactor R2(dosing Fe²⁺ at the beginning of anoxic) with dosing 3 mg/L Fe²⁺ can stably achieve the surface water class III standard. And the Fe²⁺ has higher efficiency in the phosphorus removal. The mole ratio of iron?ferrous dosing quantity? and phosphate?the increment of phosphorus removal? of R1 and R2 are 0.34:1 and 0.35:1, which are far below the reactor R4(aerobic sludge system with dosing 3 mg/L Fe²⁺) whose ratio is 0.82:1. Compared with reactor R0, the nitrate removal efficiency of R1 and R2 were enhanced, and R1 is slightly better than R2. Besides, the sludge concentration was increased and the sludge settleability was improved with dosing ferrous.Finally, we primarily analyzed the mechanism of cooperation between Fe²⁺ and the denitrifying phosphorus removal sludge. After dosing ferrous, the phosphorus concentration in the sludge EPS of R1 and R2 reduced by an average of 4.10 mg/L and 3.59 mg/L. In addition, EPS could act as a phosphorus reservoir of microorganisms with phosphorus removal function. The result stated that the removal of phosphorus in EPS is one of the ways of phosphorus removal. After a long-term operation of R1 and R2, when interrupting the ferrous dosing, the reactor could also maintain the original biological nitrogen removal efficiency. Besides, the results of high throughput sequencing showed that the microbial community structure of R1 and R2 were similar, but significant different with R0, which stated that the structural change of the microbial community may be an important reason for the strengthening phosphorus and nitrate revomal effect.