# A Cyclic Graywater Treatment Model for Sustainable Wastewater Management Applied in a Small Scale
## 3 Results
### Effect of Irrigation with Graywater on Quinoa  
#### 3.2.1 Effect on Soil Parameters  
The soil samples were collected before and after quinoa planting to examine the changes in soil salinity under cyclic irrigation with treated graywater. The average electrical conductivity of the saturated paste extract (ECe) was calculated for each cyclic treatment level (Figure 4). Overall, soil salinity increased compared to the initial value (ECe = 0.99 dS/m), with significant increases in all trials. Figure 5 shows considerable variation in ECe based on the graywater quality and treatment level, following the same trend for both cultivated and bare soils. The average ECe increased from 2.58 to 4.10 dS/m in bare soils and from 2.80 to 4.36 dS/m in cultivated soils. Figure 3: Variation in biological parameters and microbiological water quality of graywater depending on the treatment. (**a**) BOD; (**b**) COD; (**c**) fecal coliforms (FC); (**d**) total coliforms (TC); (**e**) _E. coli_; (**f**) fecal streptococci (FS); RGW—raw graywater; GWT1: graywater drained from the first treatment; GWT2: graywater drained from the second treatment; and GWT3: graywater drained from the third treatment. Figure 4: Variation in soil ECe according to the cyclic treatment. Figure 5: Variation in quinoa growth parameters. (**a**) Aerial parts; (**b**) root part. Similarly to the drained graywater section, the geometric sequence was applied to evaluate the effect of irrigation with treated graywater. Measured and calculated values for ECe followed a geometric model with low common ratios (q). Significant correlations were found between the same parameters at different treatment levels for both trials (bare and cultivated soil). This study compares the soil Ece as the function of cyclic treatment for two types of soil: bare soil and cultivated soil. For bare soil, the relationship is described by the equation y = 1.045x + 0.23, with a q value of 1.72 and a coefficient of determination R\({}^{2}\) = 0.94, indicating a strong correlation. For cultivated soil, the equation y = 1.086x + 0.21 also shows a high correlation, with a q value of 1.77 and a coefficient of determination R\({}^{2}\) = 0.94. These results suggest that both soil types respond similarly to cyclic treatment. This consistency, in response, highlights the reliability of the geometric model in predicting Ece under varying conditions. Table 4 shows the average concentrations of contaminant microbes (FC, TC, _E. coli_, and FS) in the soil. Soil irrigated with treated graywater via cyclic treatment system showed a significant reduction in pathogenic bacteria: 91%, 73%, 69%, and 84% for FC, TC, _E. coli_, and FS, respectively. The levels at the third treatment stage met the WHO recommended thresholds for the reuse of treated wastewater in agriculture, which include a maximum of 1000 MPN/100 mL for TC, 100-1000 MPN/100 mL for _E. coli_, and 35 MPN/100 mL for FS. Similarly to the previous section, a geometric sequence was applied to the microbial data to assess the impact of irrigation with treated graywater. A strong correlation was observed between the measured and calculated values for all microbes in the soils (Table 5), following a geometric model with low common ratios (q). Correlations were established for each microbe across the different treatment levels (Table 5). These correlations were negative and statistically significant.