Struvite crystallization for recovering ammonia nitrogen from landfill leachate

Key words: 
• landfill leachate /
• ammonia nitrogen /
• struvite /
• crystallization

Abstract: 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 MgSO4·7H2O and Na2HPO4·12H2O. 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 structure of struvite crystallization was destroyed under high pH value condition resulted in ammonia nitrogen dissociating 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 Mg2+,NH+4,PO3-4 were 9.5, 25 min and 1.5∶1∶1.5 respectively. Results also showed that MAP hardly absorbed heavy metal during struvite and crystallization, which was an excellent fertilizercontrolled release.