Research On Chemical Precipitation Recycle Treatment Of The High Concentration Ammonia Nitrogen Wastewater

Ammonia nitrogen removal in high concentration ammonia-nitrogen wastewater, which has become urgently solved problems at present,is catching attention of experts and scholars from all of the word.Adding Mg²⁺and PO₄^3-into high ammonia-nitrogen wastewater to form insoluble compound MgNH₄PO₄ is called the magnesium ammonium phosphate chemical precipitation method.The method for ammonia nitrogen removal with simple technology,fast reaction speed and high removal efficiency has been taken more and more attention.MAP precipitation was carried out by adding Na₂HPO₄ and MgCl₂.Based on an amount of experiments,the paper studied the relationship among pH value,reaction chemicals molar ratio and reaction time.And by orthogonal experiments the paper drew an optimal reaction condition and the sequence of actors.The effect of P:N was the most significant.The highest removal was obtained at pH 9.5.Mg²⁺:NH₄⁺:PO₄^3-molar ratio of 1.3:1:1.1 was found to be beneficial for the higher removal of NH₄⁺-N and the lower remnant of phosphate.However,reaction time showed little effect.It showed that a highest NH₄⁺-N removal of more than 98%.In addition,a set of reaction separator was developed by author.The paper also analyzed the reaction mechanism and precipitation character of the reaction product.The influence of pH on ammonium nitrogen removal follows the acid effect and the chemical equilibrium principle.The acid effect and common ion effect can explain the influence of mole ration to ammonium nitrogen removal.The reaction product is easy to precipitate,which is in favor of MAP recovering.XRD pattern indicated that the precipitate's main composition was magnesium ammonium phosphate.In order to reduce the consumption of chemicals,two methods of ammonium elimination from MAP have been investigated in present study.The study result showed that MAP decomposition residues heating under alkali conditions compromise less ammonium than that heating without alkali conditions.The MAP decomposition residues can be reused as magnesium and phosphate chemicals.Based on an amount of experiments,the paper studied the relationship among OH^-:NH₄⁺ molar ratio,reaction temperature and reaction time.And by orthogonal experiments the paper drew an optimal reaction condition and the sequence of actors. About 96-97%of ammonium in MAP powder could be released under the following conditions:OH^-:NH₄⁺ molar ratio,1:1;temperature,90℃;heating time,2 h. Ammonium incorporation into the MAP decomposition residues has been investigated in present study.Up to 93%ammonium removal was achieved by using the MAP decomposition residues as the sole phosphate and magnesium sources on pH 9.5 and reaction time 3h.The ammonium removal decreased gradually following the increase of MAP reuse cycles,and in the 4th cycle,ammonium removals of 81.62%.The avarage cost is 9.69 yuan in 5 cycles.Ammonia nitrogen can be efficiently removed from high concentration ammonia nitrogen wastewater by chemical precipitation method.MAP precipitated in the reaction decomposes under alkali and thermal conditions.Recovery of decomposition residues as Mg and P resources will save chemical costs in chemical precipitation greatly,which was proved to be a practical support for widely use of chemical precipitation.