| Ammonium-nitrogen is an important reason for causing the eutrophication of water body in petrochemical wastewater. Low treatment efficiency, high cost and large treatment system volume have become urgently solved problems at present. Based on a large number of papers and experimental researches, this paper put forward that the most promising ammonium-nitrogen removal process is chemical precipitation, which can recover the ammonium-nitrogen from petrochemical wastewater as magnesium ammonium phosphate precipitate.According to chemical precipitation theory, in the experiment, two chemicals containing Mg2+ and PO4~ ions were used to put into wastewater to generate the MgNH4P04-6H20 precipitation. So ammonium-nitrogen could be removed from wastewater as a precipitate effectively. Repeated experiments proved that optimum precipitators and stirring speed were selected as Na2HP04 12H20, 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 ammonium-nitrogen contained in the petrochemical wastewater could be quickly reduced from 1480mg/L to below 30mg/L and surplus phosphate less than 10mg/L with 10 minutes. When Na2HP04-12H20 and MgS04-7H2O were added at a molar ratio of P:Mg:N=l:1.2:1, minimum concentrations of residual ammonium- nitrogen 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 percent in 10min; (3) the precipitate yield and its composition of nutrition were similiar to the standard composition of MgNH4P04-6H2O; (4) SEM and X-ray figures indicated that the precipitate had a typical morphology of a short prismatic crystal, and its main compositon 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. To investigate the fertility of the precipitate, a set of pot trial testes was conducted. Three kinds of flowers, calendula officina lise, cabbage flower and dianthus chinens were cultivated in red earth and the precipitatewas applied as a fertilizer. The germination and growth of the selected flowers with the precipitate showed significantly greater growth ratios than those in the control pots without the precipitate. The experiment also demonstrated that over-dosing of about 2-8 times of the precipitate in the soil did not cause any problems with the flower, whereas add more precipitate, would stimulate vegetables growth. These tests proved that the precipitate as a slow release fertilizer was good for flowers' growth. So this paper is also to preliminarily design the recovering process of ammonium-nitrogen from petrochemical wastewater, and to discuss the product process of the precipitate from small experiment to industrialization.Recovery of high concentration ammonium-nitrogen from petrochemical wastewater as a slow release fertilizer could turn waste into resource, which was proved to be an optimum method to deal with petrochemical wastewater. |
