**3.2 Morphology of struvite-K precipitation**

The morphology of struvite-K was observed by using Microscope images (Olympus CX-32). **Figure 4A** shows needle-like structure. This is agreement with some reported [3, 4, 27, 28]. While for **Figure 4B**, the needle-like was mixed with block and hexagonal structure. Furthermore, there are more blocks and hexagons seen in **Figure 4C**. This shows that as the amount of magnesium increases and the removal rate of phosphorus decreases, the structure is affected which mixed with another structure. The increase in the magnesium dosage also reduces the crystal size. The average of crystal size of 22.45 μm (**Figure 4A**). This is agreement with [29] that increase magnesium dosage reduced the average crystal size. Struvite-K forms a white crystalline solid. When dried in 60°C the struvite-K precipitated into appearance of white powder as shown in **Figure 4D**. While for the struvite-K yields of 11.28 gram.

#### **Figure 4.**

*Struvite-K crystals as seen x10/0.25 of Olympus. Image captured with microscope of Olympus CX-32. (A) Initial Mg:P of 0.8, (B) initial Mg:P 1.08, (C) initial Mg:P of 1.22 and (D) image of struvite-K precipitated dried (crystal of white powder).*

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