The Removal Ammonia-nitrogen From Sewage

There are two modalities of ammonia-nitrogen in water, one is dissociation ammonium NH₃—N, the other is ammonia nitrogen NH₄⁺—N. In general, NH4+ can't generate the precipitation with negative anions directly, but some salt ammonium is undissolved, just as MgNH₄PO₄(MAP),MnNH₄PO₄,MoNH₄PO₄ and so on. So chemical precipitation method which is to put two chemicals containing Mg²⁺ and PO₄^3- ions into water, generating precipitation MgNH₄PO₄ with NH₄⁺ in water, is applied to remove ammonia-nitrogen in water. The chemical precipitation method has several outstanding advantages including briefness technology, reaction rapid, high effect remove; and especially can be used to treat high concentration of waster-water containing ammonia-nitrogen. MAP is a kind of fertilizers which can be sold for reducing the expense of chemical precipitation method running. Though large numbers of experiments some kinetic parameters, including the value of pH, the relationship between the rate of ammonia-nitrogen removal and the ratio of reagents selected in reaction, reaction time and speed of whisking and so on were obtained. The optimum conditions of technology of chemical precipitation by orthogonal experiment and single optimizing experiment were attained. Among the five kinds of chemical precipitators (MgO and H₃PO₄, MgSO₄ and Na₂HPO₄, MgSO₄ and NaH₂PO₄, MgCl₂ and Na₂HPO₄,MgCl₂ and NaH₂PO₄) can be used to remove the ammonia nitrogen effectively, particularly the MgCl₂ and Na₂HPO₄ are widely applied because of the higher rate removal of ammonia nitrogen and higher solubility. The results showed that for waster water with concentration of ammonia-nitrogen 1000mg/L initial, the rate of ammonia nitrogen removal is more than 99% under the conditions of the value of pH 9.5, speed of whisking 100r/min, the ratio of n(Mg²⁺) to n(NH₄⁺) to n(PO₄^3-) is 1.3 to 1 to 1.1, reaction time 10min ,surplus phosphorus less than 15mg/L. The flocculant can improve the effective of generating MgNH₄PO₄, the effects of PAM and PAC on the removal ammonia were observed. The results indicated that for water with concentration of ammonia-nitrogen 1000mg/L initial, when the experimental conditions were following, namely pH 9.5, speed of whisking 100r/min, the ratio of n(Mg²⁺) to n(NH₄⁺) to n(PO₄^3-) is 1 to 1 to 1, the experimental results are following, when the quantity of PAM 20mg/L, the rate of ammonia nitrogen removal is 99.01%, there is 5.38% improve on the removal of ammonia; when the quantity of PAC is 200mg/L, the rate of ammonia nitrogen removal is 98.77%, there is 5.08% improve on the removal of ammonia.