**5. Struvite as fertilizer**

One of the main concerns of applying alternative fertilizer obtained by P-recovery from waste streams is related to the potential presence of pathogens, heavy metals, and also low levels of bio-utilization [38]. However, these drawbacks are case-specific and could be solved on a technological level. Usually, the heavy metal content of struvite is below the detection limit and it is suggested that is mainly linked to total organic matter in the samples and not to the struvite crystals themselves [39]. It is already known that MAP is suitable for feeding decorative plants like grass, tree seedlings, decorative plants, vegetables, flowers, and grass gardens [40]. The main question for the agriculture industry remains the efficiency of alternative fertilizers, such as struvite, when they are used to replace (or complement) commercially available products.

The chemical nature of struvite defines it as a combined fertilizer source of nitrogen, phosphorus, and magnesium which is an important microelement for the photosynthetic systems of plants [41]. Due to the limited water solubility (Ksp value of 7.59 × 10–14), it is also a natural slow-releasing fertilizer that could provide a steady supply of plant nutrients over an extended period of time. The nutrient release could be significantly influenced and regulated by the soil microbiology and physical characteristics matching the plant utilization rate [42]. Contrarily, conventional mineral fertilizers are readily soluble and could be washed out by rainfalls and irrigation increasing the risk of surface and groundwater pollution and eutrophication [43].

Recently, the author's research group tested struvite fertilization toward maize growth which was followed for 6 months of vegetation in a test field [44]. The quantity and quality of the crops harvested were compared with control samples

*Phosphorus Recovery through Waste Transformation: Implication for an Alternative Fertilizer DOI: http://dx.doi.org/10.5772/intechopen.111856*


#### **Table 6.**

*Productivity of maize applying different fertilizers (M1000 – The absolute weight of 1000 grains).*


**Table 7.**

*Qualitative characteristics of maize while using different fertilization options.*

obtained by cultivation with conventional fertilizers. The evaluation was performed based on the yield and nutritional characteristics of the corn. According to the results obtained, the struvite is a very efficient complement to the nitrogen fertilizers (such as ammonium nitrate and carbamide) as an alternative to the normal superphosphate and triple superphosphate in the role of P source. Considering overall P availability, different struvite samples show patterns with a continuous soil release of phosphorus without peak concentrations followed by fast decline which is typical for super phosphates or rock phosphate for instance [45] (**Tables 6** and **7**).
