It is necessary to adjust reaction pH when a single kind of PO3-4 is used as phosphorus source to remove NH+4-N in a chemical precipitation process.However,this tedious step could be avoided in experiments that use the buffering effect of the composite phosphate and employ PO3-4 and HPO2-4 as phosphorus sources.pH was controlled by properly changing the proportion of PO3-4 to HPO2-4.The influences of pH,material proportion and different addition modes of magnesium on NH+4-N removal efficiency were investigated,with NH+4-N concentration in influent being 200mg/L.It showed that the ratio of HPO2-4:PO3-4 was concerned with phosphorus and NH+4-N removal.Under the condition that the total amount of phosphate is definite,the removal efficiency of NH+4-N decreased with the enhancement of HPO2-4 concentration,while the efficiency of phosphorus increased.When increasing PO3-4 concentration,it benefited the removal of NH+4-N,but the remaining phosphorus was high.The results showed that NH+4-N concentration decreased from the initial 200mg/L to 39.14mg/L with the remaining PO3-4 at 5.14mg/L if the ratio of HPO2-4:PO3-4 remained at 1:3.
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