| In this study, chemical precipitation methods were used as the pretreatment method to remove high concentration of phosphorus from the wastewater of caprolactam production by HPO method. In laboratory scale, the dephosphorization effects and the impact factors of the precipitation methods for the CaCl2, CaF2, Ca(OH)2, MgCl2with NH4Cl, Ca(NO3)2as precipitation agents were compared, and the process conditions for precipitation reaction were optimized. It was found that, for simulated phosphate wastewater, CaCl2and Ca(NO3)2showed good phosphorus removal effect. The phosphate removal efficiency by CaCl2reached above99%with Ca/P=4and pH=12; and phosphorus removal efficiency by Ca(NO3)2was above99%with pH≥11and the Ca/P ratio≥4. For the actual wastewater, when pH=11and the Ca/P ratio=3, the phosphorus removal efficiency exceed95%with CaCl2being as the precipitation agents; and when the Ca/P ratio being about2.5and the pH being about10.2, the phosphorus removal efficiency of the limewater as precipitation agent could exceed95%. Based on the results of pilot scale experiments, it was found that limewater could remove phosphorus in wastewater effectively and the phosphorus removal efficiency was above95%, with the ratio of1%lime water and wastewater being more thanl:10. Thus the phosphorus concentration of15t/h wastewater from caprolactam production by HPO method could fall to below5mg/L after pretreatment of chemical precipitation. After the mixing with all caprolactam production wastewater, it could reach200t/h and would be further treated by A/O biological process. Therefore, the effluent could completely meet the requirements of national discharge standard. The treatment process of limewater precipitation pretreatment combined with biological treatment showed high dephosphorization effects and lower agent cost. This technology could be applied for engineering reform of practical wastewater treatment with desired dephosphorization effects. |
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