## 4 Conclusions  
This study examined the growth performance and adaptability of _Desmodesmus_ sp. KNUA231 under pH and salinity stress conditions to assess its potential as a biofuel resource. The strain exhibited stable growth across a broad pH range (4-10) and moderate salinity levels (up to 5 g L\({}^{-1}\) NaCl), demonstrating its ability to thrive under diverse environmental conditions. This environmental adaptability suggests that _Desmodesmus_ sp. KNUA231 may contribute to cost-effective large-scale cultivation by reducing the sensitivity to fluctuating culture conditions. FAME analysis indicated that the biodiesel properties of _Desmodesmus_ sp. KNUA231 comply with ASTM and EN standards in specific parameters, supporting its feasibility as a renewable bioenergy feedstock. The strain exhibited a favorable fatty acid profile, contributing to desirable biodiesel characteristics such as kinematic viscosity, oxidative stability, and cold filter plugging point (CFPP). Furthermore, its high calorific value (CV) confirms its potential as an energy-dense biomass source. In addition, the strain accumulated essential nutrients while maintaining low heavy metal levels, supporting its potential as a biofertilizer. Overall, the findings highlight _Desmodesmus_ sp. KNUA231 as a valuable candidate for third-generation bioenergy production, particularly in non-optimal environmental conditions where pH and salinity fluctuations are common.  
The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app15095097/s1](https://www.mdpi.com/article/10.3390/app15095097/s1)]([https://www.mdpi.com/article/10.3390/app15095097/s1](https://www.mdpi.com/article/10.3390/app15095097/s1)), Table S1: Sequence of ITS, 18S, and _tufA_ primers; Figure S1: (a) Light microscope image of _Desmodesmus_ sp. KNUA231. (b) Phylogenetic relationship of _Desmodesmus_ sp. KNUA231 and its closely related species based on 18S rRNA sequence data. Numbers at nodes indicate percentage values derived from 500-bootstrap-analysis samples. The scale bar represents differences in nucleotide sequences, and nodes indicate percentage values derived from 500-bootstrap-analysis samples. The scale bar represents differences in nucleotide sequences; Figure S2: Daily pH variation during the 9-day cultivation of _Desmodesmus_ sp. KNUA231 under control conditions; Table S2. Summary of pH values during the 12-day cultivation of Desmodesmus sp. KNUA231 under various pH and salinity stress conditions; Table S3. Comparison of pH tolerance, salinity tolerance, and calorific value (CV) of Desmodesmus sp. KNUA231 and other microalgae species based on the published literature. Table S4. Comparison of pH tolerance, salinity tolerance, and calorific value (CV) of Desmodesmus sp. KNUA231 and other microalgae species based on published literature.  
Conceptualization, Y-S.S.; methodology, Y-S.S. and H-S.N.; validation, Y-S.S.; data curation, Y-S.S.; writing--original draft preparation, Y-S.S. and J-M.D.; writing--review and editing, J-M.D. and H-S.Y.; funding acquisition, H-S.Y. All authors have read and agreed to the published version of the manuscript.  
This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (Grant Number 2021R1I1A2055517), and the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. RS-2024-00406555).  
Not applicable.  
Data Availability Statement: The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.  
The authors declare no conflicts of interest.