# A Cyclic Graywater Treatment Model for Sustainable Wastewater Management Applied in a Small Scale
## 4 Discussion  
The experiment aimed to assess the quantity and quality of graywater treated by a cyclic treatment system (GWT1, GWT2, and GWT3), with a focus on its potential for reuse,  
Figure 7: Evaluated parameters concentrations variation in roots, stems, leaves, and seeds of quinoa. (a) Na\({}^{+}\); (b) K\({}^{+}\); (c) P; (d) N; (e) Ca\({}^{2+}\); (f) (Mg\({}^{2+}\)). particularly in terms of its effects on soil properties and quinoa growth. The results revealed several noteworthy trends that merit further scientific discussion. The treatment process yielded graywater with a slightly alkaline pH, demonstrating minimal variation across treatment stages (7.7-7.9). This suggests that the cyclic treatment system effectively stabilizes the pH, keeping it within acceptable limits for agricultural reuse. This finding is consistent with the typical pH range observed in graywater treatment, which usually falls between 7.5 and 8, indicating a neutral to slightly alkaline quality suitable for various applications. This pH range is important for ensuring the safety and effectiveness of graywater reuse, particularly in agricultural contexts, as reported in previous studies [28; 29]. According to [32], a neutral to slightly alkaline pH is beneficial for agricultural irrigation, as it minimizes the risk of soil acidification and promotes healthy plant growth. However, a marked increase in EC, especially in GWT3 compared to GWT1, indicates that the treatment leads to an accumulation of dissolved salts, particularly in the later stages of the process. These results are in line with previous research, which also documented increased salinity after graywater treatment [33; 34], reinforcing the idea that salinity control is a key challenge in graywater reuse for irrigation. The increase in EC of treated graywater is influenced by various electrochemical processes, particularly through methods such as electrocoagulation and high-voltage electric fields. These treatments not only enhance the EC but also improve the overall quality of graywater for potential reuse. The reduction in BOD\({}_{5}\) and COD across all treatment stages highlights the efficacy of cyclic treatment in reducing organic pollutants. In our experiment, the raw graywater initially exceeded the COD limits outlined in the NT 106.03 standard, but the treatment process progressively brought COD levels into compliance with these regulatory thresholds. This suggests that the cyclic treatment system is effective at removing organic contaminants, a critical factor for ensuring that treated graywater meets water quality standards for agricultural reuse. The significant reduction in BOD\({}_{5}\) and COD also aligns with previous findings on the benefits of treatment systems in reducing organic load [35; 36]. Similarly, Ref. [29] reported the efficiency of a graywater treatment system based on aeration and filtration in removing the BOD\({}_{5}\) and COD parameters was 98-100 and 76-100%, respectively. Although the cyclic treatment system successfully removed a substantial proportion of targeted pathogens, the microbial load in the treated graywater still failed to meet the stringent standards set by the WHO. This underscores a critical limitation of the system, as effective pathogen removal is essential for ensuring safe reuse of graywater in agriculture. The gap between the treatment's performance and the WHO's guidelines suggests the need for further research to optimize microbial disinfection processes and enhance the overall safety of treated graywater [37]. In fact, various treatment methods have been explored, demonstrating significant effectiveness in pathogen reduction. According to [38], multi-stage filtration, including sand, activated charcoal, and coconut husk, achieved 100% removal of _E. coli_ and coliforms in treated graywater. Moreover, Green roofs combined with chlorination effectively reduced total coliforms by up to 1.2 log units, with chlorination ensuring pathogen inactivation for up to three days [39].