**3. Results and discussion**

#### **3.1 Effect different initial of Mg:P ratios on % P removal and precipitate**

Bubble column reactor was used in laboratory studies with hopefully, it can be implementation in wastewater industry. From a structural point of view, they are very simple units equipped with added a dose pump as mixing system that allows for the homogenization of the wastewater with the reactants. The mixing condition inside the reactor represents a fundamental aspect because it affects the struvite formation [17]. An effective mixing promotes the crystals nucleation and growth by improving the mass of ions from the solution to the solid phase. Generally, completely mixed reactors can operate continuously or in batch mode. A batch column reactor works according to a series of phase and the struvite-K production and precipitation occur in the same unit (**Figure 2**).

In this study, we used MgCl2.6H2O as magnesium source which have advantages of being very soluble allowing to recovery a precipitate with a high purity degree [18]. Due to easy management was used in many studies through which the kinetics of the nucleation process have been assessed [19, 20]. While the pH was maintained in alkaline condition of 11 which following based on [21]. Since the conditions favorable precipitation of struvite-K. Based on **Figure 3** shows that P removal rate was decreased from 98.5–80% which increasing of molar ratios of Mg:P from 0.8 to 1.22 since strong influence of precipitation in many scientist [22]. While for hydraulic retention time we maintained at 1.98 h; since in around of this was much more consistent than the rate reported in the literature and no effect with difference of HRT in precipitation [3, 4]. Furthermore, P recovery of struvite-K we conducted only for Mg:P of 0,8 since these concentrations was effective for % P removal than others with precipitate of Mg:P of 0,7 and K:P of 1 are shown in **Table 2**.

The optimal molar ratios must be assessed case-by-case as it depends heavily on the chemical–physical characteristics of wastewater and the reactor used. On the contrary, other works in which unconventional reagents were exploited, found that greater dosages are necessary. For example, Quintana et al. [23] found a strong influence a Mg:P molar ratio on the abatement of phosphate amount and the major removal was detected when used MgO dosed at molar ratio of 1.5. Moreover, the authors observed that the increase of the molar ratio promoted the removal rate growth (Quintana et al. [24]). In agreement with this consideration, Jaffer et al. [25] affirmed that with Mg:P addition lower than 1.05 the precipitation resulted was greater to avoid the formation of magnesium sodium phosphate [4].

**Figure 2.** *Percentage of P removal with different of initial of Mg:P ratios concentration.*

*Simultaneously Recovery of Phosphorus and Potassium Using Bubble Column Reactor… DOI: http://dx.doi.org/10.5772/intechopen.100103*

**Figure 3.** *Procedure for measure exchangeable cation and CEC via NH4.*


**Table 2.**

*Effect of the magnesium dosage on the Mg:P molar concentration ratio in precipitate.*

However, an excess of Mg can cause the formation of magnesium phosphate and reducing the precipitation of struvite which following for P removal rate. Korchef et al. [26] observed the phosphate removal caused by precipitation for Mg:P molar ratio under 4 and newberyite (MgHPO4.3H2O) and cattiite (Mg3(PO4)2.22H2O) formation for Mg:P = 5.
