Simultaneous Ammonia Nitrogen And Phosphorus Recovery By Struvite From Wastewater Treatment Plant

The accumulation of nitrogen and phosphorus compounds by discharge of wastewater is one of the main causes of eutrophication in water bodies. How to control nutrients pollution high-efficiency and economically has become an urgently solved problem at present. On the part of wastewater treatment, control over the wastewater of nitrogen and phosphorus has shifted from removal to recovery. Biological nutrient removal for eutrophication control creats a prerequisite for nitrogen and phosphorus recovery. Because nutrient-enriched liquid could be produced in some of the treatment units, such as anaerobic tank, sludge digester, sludge thickening and dewatering pond. The technology of struvite precipitation researched in this paper could be applied to recovery nitrogen and phosphorus simultaneously.According to chemical precipitation theory, in the experiment, two chemicals containing Mg²⁺ and PO₄^3- ions were used to put into wastewater to generate the struvite(MgNH₄PO₄·6H₂O) precipitation. So ammonium-nitrogen and phosphorus could be recovered from wastewater as a precipitate effectively. Repeated experiments proved that optimum precipitators and stirring speed were selected as Na₂HPO₄·12H₂O,MgSO₄·7H₂O and 100r/min, respectively. Then this experiment made use of orthogonal experiment and single optimizing experiment to determine optimum process parameters. The results indicated that the highest percetages recovery of ammonium-nitrogen and phosphorus reached about 88% and 98% respectively with 10 minutes. When Na₂HPO₄·12H₂O and MgSO₄·7H₂O were added at a molar ratio of N:P=1.1, Mg:P=1.3, the maximum recovery of ammonium- nitrogen and phosphorus occurred between pH 9.0 and 9.5. Moreover, physical chemistry characterstics of the precipitatate were also studied in this experiment. And some results could be obtained: (1) the precipitate was easily settled; (2) SV was below 20 percents in 10min; (3) the precipitate yield and its composition of nutrition were similiar to the standard composition of struvite;(4) SEM indicated that the main compositon of precipitate was magnesium ammonium phosphate. In addition, as low solubility and containing N, P and Mg vegetable nutrition elements, the precipitate could be used as a fertilizer.Simutaneous recovery of ammonium-nitrogen and phosphorus from wastewater treatment plant by struvite precipitation could complement resources of nitrogen and phosphorus, which satisfies the sustanable development request of society, economy...