Seasonal assessment of groundwater quality and irrigation suitability using a solar-powered AgNP/activated carbon treatment system in a coastal aquifer.

The increasing water scarcity, groundwater degradation, and climate variability have increased the demand for sustainable groundwater management strategies in arid and semiarid regions. This work presents an integrated framework for groundwater monitoring and irrigation suitability assessment of groundwater from 13 borehole at a university campus in Alexandria, Egypt, under climate change conditions. The developed system was implemented via a field-scale, solar-powered fixed-bed column packed with a green-synthesized silver-nanoparticle/activated-carbon nanocomposite (AgNPs/AC-NC). Groundwater from the 13 wells was sampled over 4 consecutive seasons to investigate the spatial and temporal variations in physicochemical, microbiological, and hydrochemical characteristics before and after treatment. In addition, water quality indices were calculated to assess water suitability for irrigation in accordance with the Food and Agriculture Organization of the United Nations (FAO) guidelines. The preliminary hydrochemical analysis of the raw samples indicated that sodium and bicarbonate ions were the dominant ions, which is typical for the sodium-bicarbonate water type, with elevated salinity, turbidity and dissolved constituents during the warm seasons. The AgNPs/AC-NC treatment resulted in reductions in salinity-related parameters, major dissolved ions, and irrigation hazard indices averaged across all wells and seasons. Most of the physicochemical parameters showed an overall reduction of 30-80%, with the most significant reductions in sulphate (80.3%), alkalinity (71.0%), sodium and potassium (67.4%), nitrate (52.6%), electrical conductivity (54.2%), chloride (53.5%), and total dissolved solids (47.3%). In addition, the potential salinity, residual sodium carbonate and total hardness decreased by 50-72%, and the total and fecal coliform concentrations were < 1 CFU/100 mL in most samples. While most of the parameters were within the FAO irrigation standards, copper, nitrite, acidity and turbidity remained above the standard, suggesting that a dedicated copper removal and polishing step is still needed. Nonetheless, the framework provides a practical, decentralized groundwater treatment and irrigation reuse model that is climate-resilient, making it suitable in water-scarce regions.