Blue/green water footprint reduction strategy: Assessment of wastewater recovery and nutrient release

This thesis aimed to synthesize a hydrogel containing municipal sewage sludge (AÇ), which poses environmental disposal challenges. In this context, hydrogels containing guar gum (GG), borax (B), glycerol (Gl), and AÇ were synthesized, and the optimum hydrogel was investigated in detail. First, the effects of GG (%), AÇ (g), Gl (mL), and B (%) on the response variables of water swelling, mass loss, and cycle number were evaluated using the Plackett–Burman design. Based on the results, the AÇ and Gl levels were fixed, and a second-stage optimization design using Response Surface Methodology (RSM) was applied to examine the curvature of the swelling ratio. As a result of the RSM design, the levels were determined as GG = 3.4% and B = 15%. The AÇ-added hydrogel synthesized under this formulation exhibited a swelling capacity of 1255%, a mass loss of 33.3%, and a gel fraction of 52.5%, while showing higher water retention capacity compared to hydrogels without AÇ. The predictive power of the Random Forest (RF) algorithm and the DoE models was compared, and the RF model was found to have the highest predictive power (R²= 0.8242). FTIR, XRD, and SEM analyses indicated that AÇ was integrated into the hydrogel matrix. Nutrient and heavy metal release tests showed that the initial burst release was controlled by the washing process. The results demonstrated that the AÇ-added hydrogel could be an environmentally friendly and cost-effective material that reduces the blue/green water footprint and provides nutrient release under agricultural drought conditions.