Struvite crystallization for recovering ammonia nitrogen from landfill leachate
鸟粪石结晶法回收垃圾渗滤液氨氮研究

A lab-scale study was conducted to precipitate the ammonia from landfill leachate in the form of magnesium ammonium phosphate( MAP) by applying such chemicals as MgSO_4·7H_2O and Na_2HPO_4·12H_2O. The influences of pH value, reactive time and concentration on removal rate of ammonia nitrogen were tested. Results showed that the feasible pH values of crystallization and precipitation were between 9 and 9. 5. The struc-ture of struvite crystallization was destroyed under high pH value condition resulted in ammonia nitrogen dissocia-ting from MAP, which reduced the removal rate of ammonia nitrogen. Results also demonstrated that ammonia nitrogen was effectively reduced from initial 3 500mg/L to final 175 mg/L, which removal efficiency reached 95% with crystallization and precipitation method when the optimal pH, precipitation time mole ratio of Mg~(2+) , NH_4~+ ,PO_4~(3-) were 9. 5, 25 min and 1.5:1:1.5 respectively. Results also showed that MAP hardly absorbed heav-y metal during struvite and crystallization, which was an excellent fertilizer-controlled release.