## 3 Results and Discussion
### Nutrient and Metal Composition Analysis  
Trace elements and heavy metals in biological samples can be analyzed using ICP-MS and ICP-OES, which are widely applied in assessing the potential of biofertilizers. In this study, the macronutrient, micronutrient, and heavy metal concentrations in the microalgal-derived biofertilizer were evaluated against EU fertilizer standards [65]. Macronutrients were converted into their oxidized forms for direct comparison with EU regulations. The results confirmed that key nutrients such as phosphorus, potassium, calcium, magnesium, sodium, and sulfur were present at sufficient levels (Table 6). For comparison, the EU requires a minimum of 10,000 mg kg\({}^{-1}\) P\({}_{2}\)O\({}_{5}\) for phosphorus, 30,000 mg kg\({}^{-1}\) K\({}_{2}\)O for potassium, 12% CaO for calcium, 5% MgO for magnesium, and 10% SO\({}_{3}\) for sulfur. Sodium remained within the acceptable limits, ensuring no risk of excessive salt accumulation.  
Micronutrient analysis showed that zinc, copper, manganese, and iron concentrations were above the EU threshold for inorganic micronutrient fertilizers, which requires at least 2% for liquid fertilizers and 5% for solid fertilizers. However, boron and molybdenum were not detected, which does not meet the minimum EU requirement for micronutrient fertilizers (boron \(\geq\) 10 mg kg\({}^{-1}\), molybdenum \(\geq\) 5 mg kg\({}^{-1}\)). While the biofertilizer provides a rich source of trace elements required for plant metabolism, supplementation with boron and molybdenum may be necessary to achieve a more balanced nutrient profile.  
Heavy metal concentrations were within safe limits according to EU organic fertilizer regulations. Arsenic was well below the EU limit of 40 mg kg\({}^{-1}\), cadmium remained significantly lower than the EU limit of 1.5 mg kg\({}^{-1}\), and lead was well below the threshold of 120 mg kg\({}^{-1}\). These results suggest that the microalgal biofertilizer offers a high nutrient profile while maintaining environmental safety, highlighting its potential for sustainable agricultural use.  
The overall findings indicate that _Desmodesmus_ sp. KNUA231 could serve as a promising alternative to conventional fertilizers. The high macronutrient and micronutrient content ensures an adequate nutrient supply for plant growth, while the low heavy metal  
\begin{table}
\begin{tabular}{c c c} \hline \hline  & **Element** & **Concentration (mg kg\({}^{-1}\))** \\ \hline  & K & 8495.826 \\  & Ca & 1558.945 \\  & Mg & 2148.444 \\ Macronutrient & Na & 1519.323 \\  & S & 5595.413 \\  & P & 5877.109 \\  & Si & 74.623 \\ \hline  & Zn & 55.919 \\  & Cu & 20.072 \\  & Mn & 407.678 \\ Micronutrient & Fe & 1972.932 \\  & B & N.D. * \\  & Mo & N.D. \\ \hline  & As & 0.482 \\ Metal & Cd & 0.02 \\  & Pb & 0.366 \\ \hline \hline \end{tabular} \({}^{*}\)N.D.(Not Detected): below 10 mg L\({}^{-1}\).  
\end{table}
Table 6: Nutrient and metal composition analysis of _Desmodesmus_ sp. KNUA231.  
levels minimize environmental contamination risks. Moreover, microalgae-based biofilet-tilizers can be produced sustainably, reducing dependency on synthetic fertilizers and mitigating the ecological impact of agricultural practices. However, the absence of certain essential micronutrients, such as boron and molybdenum, suggests the need for further optimization in nutrient formulation. Future research should explore the supplementation of these missing elements and assess long-term soil and crop responses to microalgal biofertilizer application.