**1. Introduction**

#### **1.1 Bubble column reactor for struvite-K precipitation**

Magnesium potassium phosphate hexahydrate, commonly known as struvite-K, is a sparingly crystallize consisting of equal molar amount of magnesium potassium and phosphate and six water of hydration, hence the chemical formula is MgKPO4.6H2O. Struvite-K is formed according to the following reaction:

$$\text{Mg}^{2+} + \text{K}^\* + \text{PO}\_4^{3-} \rightarrow \text{MgKPO}\_4.6 \text{H}\_2\text{O} \tag{1}$$

Struvite-K has been synthesized to show its viability for phosphorus and potassium removal from wastewater [1–4] and naturally occurring. Tanaka [5] reported that phosphorus and potassium from effluents of livestock wastewater contains (5.5 mM) and (63.9 mM), respectively. This is a new resource for potassium and phosphorus demand for use as fertilizers which following global population in every year. It was estimated the world population to reach between 9 and 10 billion by 2050 [6, 7].

Struvite-K precipitates as a white powder needle-like structure, which tends to form scale on surfaces of equipment. Struvite-K scaling is a well-recognized problem in many industrial processes and domestic applications. The problem is that not only from pipes but also pumps, centrifuges and aerators can be blocked by struvite [8–10]. In the other hand, this is not problem but solution to supplying nutrient on crop growth.

Struvite-K, similar to NH4-struvite has a desired low solubility and chemical composition of Mg:K:P (1:1:1). It also has a high market value in the agricultural area (Sean 2018). It is called struvite-K because the K replaces the NH4 in struvite (MgNH4PO4.6H2O). The present study, we used synthetic wastewater was designed using bubble column reactor to simulate effluent from livestock wastewater to recovery of phosphorus and potassium as struvite-K which used as fertilizers for increasing global food production.

#### **1.2 Implementation on crop growth**

Most of the nutrients absorbed by plants come from organic matter. Therefore, the unique fertilizer formula comes from compost or struvite-K precipitate. They provide a rich source of nutrients and can be added to the soil to promote the growth of various crops. Therefore, compost and struvite-K precipitation are intended to serve the society by increasing farmers' incomes to revitalize the soil and increase farm yields. We fertilized the two fertilizers from compost and struvite-K precipitate, in order to evaluate the effects of fertilizer on soil and yields of radish (*Raphanus sativus* L.) and Komatsuna (*Brassica rapa var. perviridis*).

#### *1.2.1 Radish (*Raphanus sativus *L.)*

Radish (*Raphanus sativus L*.) belongs to the genus and species of *Radish* in the *cruciferous* family. Radishes are grown and consumed all over the world and are considered part of the human diet, although it is not common in certain populations. It is one of the most important and popular root vegetables in tropical, subtropical and temperate regions of the world (including Japan). It is grown as an annual and biannual vegetable crop, depending on its planting purpose. Radishes are mainly cold-season vegetable crops. Asian varieties can tolerate higher temperatures than European varieties. In a mild climate, radishes can be grown almost all year except for the summer months [10]. Its young roots can be eaten raw in salads or cooked as vegetables. It has a spicy taste and is considered an appetizer. Young leaves can also be cooked and eaten as vegetables. Radish preparations are useful for liver and gallbladder diseases. Roots, leaves, flowers and pods are active against Gram-positive bacteria, urinary system diseases, hemorrhoids and stomach pain. In addition, the salt extracted from the roots can be dried and burned into white ash, which can be used to relieve stomach problems [11].

#### *1.2.2 Komatsuna (Japanese mustard spinach)*

Japanese mustard spinach (*Brassica rapa var. perviridis*) is also called Komatsuna in Japanese. It is a common and popular leafy vegetable in the Japanese diet.

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

Komatsuna contains low energy and high nutrients, which is very effective in lowering serum cholesterol. On the other hand, Komatsuna has a compound called sulforaphane, which can help our body fight cancer. Sulforaphane actively kills cancer stem cells and slows the growth of tumors [12]. Komatsu greens are rich in calcium and are commonly used in kimchi in Japan and as feed crops in many Asian countries.

In 2019, the production of Komatsuna in Japan increased by 26.5% compared with 2006, and the planting area increased by 29.2%, with a total output of 114,900 tons [13]. Komatsuna can be worn in relatively temperate regions most of the year, but it is usually grown as a cool seasonal crop (spring and autumn). It can tolerate some extreme cold and hot conditions, but it cannot stand for long periods of time [14]. Economically important members of this family include vegetables such as broccoli, cabbage, chinese cabbage, radish, cauliflower as well as the oil crop canola [15].
