MAP technology for nitrogen and phosphorus removal of biopharmaceutical wastewater

1. Overview of MAP method

MAP technology is to add some ions in the wastewater, so that it reacts with the nitrogen and phosphorus ions in the wastewater to form a precipitate, and finally filter it to achieve the purpose of nitrogen and phosphorus removal. The specific operation is: add Mg2+ to the wastewater containing nitrogen and phosphorus elements, if the PO43- content is small, it can be added according to the actual situation, until the NH4+, PO43- and Mg2+ ions in the wastewater are supersaturated.

This method can not only effectively remove the high concentration of ammonia nitrogen and phosphate in the wastewater at the same time, but also does not produce some nitrogen oxide as traditional treatment methods. MAP produced at the end of the reaction can act as a catalyst to improve the reaction speed in wastewater. At the same time, if it is heated, it can be decomposed to produce NH and MgHPO4, which can be recycled again, and the latter can still play the role of nitrogen and phosphorus removal in wastewater. In addition, due to the large amount of nitrogen, phosphorus and magnesium in MAP, it is widely used in various industries, such as agricultural fertilization, medicine, coatings and soft foam flame retardants.

At present, because of its pollution-free and recyclable characteristics, MAP technology has been widely used in wastewater treatment in various industries such as urine, mining, livestock industry, food processing industry and metallurgical coking industry. In addition, MAP technology has also played a great role in the treatment of landfill leachate and sludge anaerobic digestion solution.

2. Factors affecting the treatment of nitrogen and phosphorus wastewater by MAP method

2.1 Experimental content

2.1.1 Effect of pH

If MAP technology is used to treat wastewater containing ammonia nitrogen ions, the influence of pH on the experimental results should be analyzed. Generally, the treatment effect is most obvious when pH8.5 ~ 10.5. Because in an alkaline environment, the greater the pH, the less MAP dissolves, and is only soluble in acids but not bases. Therefore, NaOH and HCl are used to regulate the pH in the wastewater so that it can always be maintained at about 10. Normally, the main reaction in wastewater occurs at pH7 ~ 10.5. If pH is lower than 7, the mass fraction of PO43- is low, which will hinder the occurrence of its reaction; If the pH is higher than 10.5, the ammonium magnesium phosphate will be decomposed, and the free ammonia nitrogen will react with magnesium ions to form Mg3(PO4)2 precipitation, which is more unfavorable to the reaction.

2.1.2 Influence of reaction temperature

Temperature will also have a great impact on the process of nitrogen and phosphorus removal, the test found that the removal of ammonia nitrogen in wastewater at 25 ~ 30℃, the most obvious effect. The experiment shows that before the temperature is 30℃, the removal effect of ammonia nitrogen is positively correlated with the temperature, that is, the higher the temperature, the better the effect. However, when the temperature is higher than 30℃, the removal effect of ammonia nitrogen decreases, because the temperature greatly affects the ionization of NH4OH, HPO4- and MgNH4PO4 contained in the solution. However, not all solutions will be greatly affected by temperature. For example, MAP technology is used to remove nitrogen and phosphorus from landfill leachate with a mass fraction of 15%-35%, which is basically unaffected by temperature changes.

In summary, temperature is still an important factor affecting nitrogen and phosphorus removal. Therefore, it is necessary to ensure that the experiment is carried out at 25 ~ 30℃. MAP technology can be used in any season in our country.

2.1.3 Influence of reaction time

The reaction rate in wastewater will slow down with the increase of time, because the concentration of ammonia nitrogen in the solution gradually decreases with the increase of time. The experimental results show that the removal efficiency of ammonia nitrogen increases with the increase of reaction time, and the concentration of residual ammonia nitrogen decreases. However, the power consumption also increases correspondingly, and the processing cost is high.

In the test, the time of fast stirring 180r/min was 1min, and the time of slow stirring 30min was 120r/min. In practice, it can be determined according to the water quality test. The relationship between the removal effect of nitrogen and phosphorus and the molar ratio of Mg and N was analyzed by controlling the molar ratio of Mg and N in a certain pH, temperature and time range.

When the initial mass fraction of NH4+-N is 150mg/L, pH=10, when the initial mass fraction of Mg: N increases from 0.2:1 to 1.2:1 (0.2:1, 0.4:1, 0.6:1, 0.8:1, 1:1, 1.2:1), the removal rate of NH4+-N, the removal rate of PO43-P and Mg are analyzed: The relationship between the mole ratio of N.

2.2 Results and discussion

2.2.1 Influence of different Mg: N molar ratio on ammonia nitrogen removal

The effect of Mg: N molar ratio on the removal rate of ammonia nitrogen is shown in Figure 1. It can be seen from the results that the pH is controlled at about 10 and the experimental temperature is 20-30 ℃. After complete precipitation, it can be seen from the experimental data that the removal rate of ammonia nitrogen changes with the change of the molar ratio of Mg: N, and the Mg: N increases from 0.2:1 to 1: 1, the percentage of ammonia nitrogen removal increased from 33.98% to 83.03%, and MgNH4PO4·6H2O precipitation was generated from it, and the theoretical removal rate ratio of n(Mg2+) : n(NH4+) : n(PO43-) was 1:1:1.

2.2.2 Effect of Mg: N molar ratio on phosphorus removal

Figure 2 shows the effect of different Mg: N molar ratios on phosphorus removal rates.

The ratio of magnesium to nitrogen was increased from 0.2:1 to 1:1, and the removal rate of phosphorus was increased from 73.14% to 94.17%, and a high removal rate had been achieved. In the course of the experiment, attention should be paid to controlling the content of magnesium to avoid its excessive and reduce the removal rate of nitrogen and phosphorus. In general, adding an appropriate amount of magnesium can increase the removal rate. The ratio of phosphorus to nitrogen is generally kept in the range of 1.0 ~ 1.1. Because the same ion will speed up the reaction rate, it will also control the magnesium-phosphorus ratio to 1.3:1 incorone.

2.3 Conclusion

1) When the test temperature is 20 ~ 30℃, pH is controlled at 10, and the ratio of n(Mg2+) : n(NH4+) : n(PO43-) is 1.3:1:1, the removal rate of ammonia nitrogen and phosphorus is > 90%.

2) With the main purpose of removing ammonia nitrogen, increasing the content of Mg2+ and PO43- in actual water treatment can increase the amount of ammonia nitrogen removed. However, if the phosphoric acid content in the reaction increases, the residual phosphorus content after the reaction increases, resulting in new pollution. Therefore, it is usually adopted to increase the magnesium salt content to speed up the reaction, and thus improve the removal rate of ammonia nitrogen. If the magnesium content is not up to standard, a large amount of precipitation of MgNH4PO4·6H2O cannot be formed.

3. Feasibility of MAP method as pretreatment for nitrogen and phosphorus removal of bioengineering pharmaceutical wastewater

Ammonia nitrogen in pharmaceutical wastewater mainly comes from fermentation wastewater and is the main metabolic by-product in the process of cell culture. TP(total phosphorus) in wastewater is mainly derived from phosphate buffer solutions in the form of PO43-, HPO42- and H2PO4- used in downstream purification of target proteins. Adding magnesium salt can precipitate MgNH4PO4·6H2O which is insoluble in wastewater. The method can be applied to the pretreatment of biological engineering pharmaceutical wastewater for nitrogen and phosphorus removal.

In order to ensure that the nitrogen removal rate of A2O process reaches 65% ~ 85%, the phosphorus removal efficiency reaches 75% ~ 85%, and the phosphorus removal efficiency of PAC(coagulant) and other chemical precipitation methods reaches more than 80%. In order to ensure that the ammonia nitrogen concentration in the discharged sewage is less than 30mg /L, the TP concentration should be 4mg/L to meet the municipal requirements. In the treatment process of A2O+ chemical precipitation, the ammonia nitrogen concentration should be less than 120mg/L, and the TP concentration should be less than 100mg/L. According to the process requirements, the ammonia nitrogen content in the fermentation wastewater is generally 500 ~ 1500mg/L, and the TP content in the purified wastewater is generally 500 ~ 1200mg/L. The phosphorus removal efficiency of this method is more than 95%, and the concentration of ammonia nitrogen and total nitrogen after pretreatment are lower than 75mg/L and 60mg/L, respectively. The combination of A2O process and chemical precipitation can make the wastewater discharge up to the standard.

4. Application examples

The construction technology of "reaction precipitation +UASB(upflow anaerobic sludge bed)+A2O+ coagulation precipitation + disinfection" was selected to treat the wastewater of 80t/d bioengineering pharmaceutical plant. After sorting and collecting enterprise wastewater, the cell culture and purification wastewater is collected into the reaction sedimentation tank, and magnesium chloride is added for reaction to produce precipitation to pre-remove ammonia nitrogen and phosphorus, and then pumped into the concentrated wastewater collection tank, and the two streams of wastewater are self-flowing to the comprehensive regulation tank. Before the pre-decomposition of organic matter in the wastewater, the wastewater in the regulation tank should be transferred to the pre-hydrolysis tank and UASB reactor by using the lifting pump. The COD must be removed and then transferred to the anaerobic tank before hydrolysis can be carried out. The nitrogen, COD and TP removal operation can be carried out successively by the art-flow into the anoxic and aerobic tank. PAC and PAM(flocculant for sewage) were added to the supernatant after separation of sludge and water to complete the phosphorus removal. Finally, adding sodium hypochlorite to complete the disinfection can be discharged into the municipal sewage network. After the design test, the water quality of the inlet and outlet of the sewage station is shown in Table 1.

As can be seen from Table 1, the water quality of pharmaceutical wastewater treated by "MAP precipitation +UASB+A2O+ coagulation precipitation + disinfection" process meets the take-over standards of municipal sewage treatment plants, and the removal rates of ammonia nitrogen and TP by MAP method are above 95%. The results showed that the ammonia nitrogen and TP were removed by precipitation, and the MAP process had a good effect on nitrogen and phosphorus removal and could be used as a treatment process for pharmaceutical wastewater.