Experimental study on phosphorus form of sludge and response surface method to optimize phosphorus release

Based on the characteristics of the process flow of the sewage treatment plant, different process sections were selected to determine the phosphorus concentration in order to determine the optimal range of phosphorus release conditions from sludge. The results showed that the phosphorus content in the sludge was the highest, accounting for 68% of the phosphorus in the sewage plant. The total phosphorus (TP) concentration in the sludge was 47.12 mg/g, and inorganic phosphorus was the main component, accounting for 89.3% of the TP. Aiming at the composition characteristics of phosphorus in sludge, the experiment adopted low temperature pyrolysis coupled acid hydrolysis and addition of ethylenediamine tetraacetic acid (EDTA) to release phosphorus in sludge. The process was optimized according to Box-Behnken Design experiments and response surface methodology. The single effect and interaction effects of pH values (X₁), reaction temperature (X₂) and EDTA concentration (X₃) were investigated, and the regression equation was established. The results showed that the regression equation had a good fit (R²= 0.987 0). The linear effect of X₁ and the curve effect of X₁² on the phosphorus release rate were extremely significant. Combined with economy and practicality, the optimal process conditions for selecting phosphorus release from sludge were: pH was 4, reaction temperature was 53 ℃, EDTA concentration was 14.5 mmol/L, and the phosphorus release rate of the verification experiment was 62.85%, and the forecast value of regression equation was 62.91%. The simulated values agreed well with the predicted values, which could provide technical support for the sludge phosphorus release process and subsequent phosphorus recovery technology applications.