| The surface treatment process of aluminum profiles uses a large amount of phosphorus-containing chemicals,resulting in excessive phosphorus content in the effluent,and direct discharge will seriously endanger the water environment.The eutrophication of water is one of the most common problems in water pollution,and the biggest threat to the water environment.Phosphorus is the key factor affecting eutrophication.Therefore,it is especially important to control the total phosphorus content in wastewater discharge.The text research wastewater has high acidity and TP,which is a typical high-phosphorus wastewater.In this paper,the removal and recycling of phosphorus from the surface treatment wastewater of aluminum profiles are studied.Before the treatment,the existence form of phosphorus in the wastewater was analyzed,and the soluble phosphate was determined as the main form,and the phosphorus removal by chemical precipitation was determined.First,calcium hydroxide?CaO?and sodium metaaluminate?NaAlO2?were used as precipitants to carry out one-step precipitation experiments,and the effect of dosage on phosphorus removal was observed.On the basis of one-step precipitation,a step-by-step precipitation process was experimented.The treatment process of calcium oxide pretreatment desulfurization,struvite precipitation and recovery of phosphorus,and subsequent treatment of PAC flocculation precipitation was finally determined.The specific research contents and results are as follows:?1?Analyze the wastewater quality,the TP concentration is 24500 mg/L,the SO42-concentration is 55000 mg/L,and the pH is 0.6.?2?In the separate precipitant dosing test,when CaO and NaAlO2 were added at 81.2g/L and 88g/L,respectively,the remaining amount of phosphorus reached the minimum,50.0mg/L and 416.4mg/L,respectively.The amount is still not up to the discharge standard and the dosage is too much.Calcium oxide alone was added to the experiment.When the dosage was 38g/L,the removal rate of sulfate was more than 90%,and the phosphate concentration was basically unchanged,which achieved the separation effect of sulfate and phosphate.Therefore,the calcium oxide dosage was 38 g/L,stirred for 30 min,and allowed to stand for 1 h as a pretreatment process for the phosphoric acid-containing wastewater.?3?In the step-by-step precipitation experiment,after pre-treatment with calcium oxide,the phosphorus-concentrating agents of[Mg?OH?2+NH4Cl],NaAlO2 and CaCl2 were separately precipitated at different initial pH and dosage conditions.Experiments show that the[Mg?OH?2+NH4Cl]combination precipitant has better phosphorus removal effect than NaAlO2 and CaCl2,and can recover phosphorus from struvite.?4?In the experimental study on the recovery of phosphorus from the struvite precipitation method,[Mg?OH?2+NH4Cl],[MgCl2·6H2O+NH4HCO4]and[Mg5?CO3?4?OH?2·4H2O+NH4Cl]Three groups of phosphorus-reducing agents were used to carry out phosphorus removal research,and a[Mg?OH?2+NH4Cl]combination precipitant was obtained.The initial pH=4,the Mg:N:P molar ratio was 1.6:1:1,the reaction time was30 min,and the reaction time was 30 min.The treatment was better under the condition of20 min.The total phosphorus residue was 4.91 mg/L,the total phosphorus removal rate was99.98%,and the pH after the reaction was 8.62.[MgCl2·6H2O+NH4HCO4]combined precipitant at initial pH=7,Mg:N:P molar ratio of 1.05:1.2:1,reaction time 30min,standing for 20min,the residual amount of TP in the wastewater is 5.72mg/L,the total phosphorus removal rate is 99.98%,after the reaction The pH value is 7.55;[Mg5?CO3?4?OH?2·4H2O+NH4Cl]combined precipitant,at initial pH=4,Mg:N:P molar ratio is 1.2:1.1:1,reaction time 30 min,standing Under the condition of 20 min,the residual amount of TP in the wastewater was 2.98 mg/L,the total phosphorus removal rate was99.99%,and the pH after the reaction was 7.85.?5?XRD pattern and scanning electron microscopy analysis were carried out on the precipitate produced by the struvite method to recover phosphorus,and the main component of the reaction product was determined to be magnesium ammonium phosphate.By comparison,the[Mg5?CO3?4?OH?2·4H2O+NH4Cl]group of reagents was selected as the final precipitant for the recovery of phosphorus from the struvite method.According to the nutrient element analysis of the struvite precipitate formed under the optimal conditions,the mass fraction in P2O5 reached 25.22%,which is equivalent to the high-grade phosphate rock,and the economic value of the recovered struvite was determined.Finally,PAC flocculation and sedimentation were used for subsequent treatment.Under the condition of PAC dosage of 3g/L and reaction time of 30min,the residual amount of TP was further reduced to 0.898mg/L,reaching the grade C standard of total phosphorus emission in the standard for sewage quality in urban sewage?GB 31962-2015?. |
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