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The management of wastewater from carwash centers continues to pose a significant global challenge, with the quest for treatment methods that are both effective and economical proving particularly daunting. This underscores the importance of exploring natural materials for wastewater treatment. However, knowledge regarding the efficacy of bio-functionalized wheat straw and pistachio shells specifically for carwash wastewater treatment remains limited. This study explored the potential of wastewater treatment using bio-functionalized agricultural waste materials, specifically wheat straw and pistachio shells. Experimental setups included treatment plants using wheat straw alone, pistachio shell alone, a mixture of both, and a series connection. Removal efficiencies across various water quality parameters revealed the series connection as the most effective treatment, achieving exceptional removal efficiencies for critical parameters such as fat, oil, and grease, total suspended solids, and turbidity. The Mixture treatment demonstrated synergistic effects, surpassing individual treatments in removing contaminants such as Arsenic, Biochemical Oxygen Demand, cadmium, Chemical Oxygen Demand, fluorides, ammonia nitrogen, and surfactants. More precisely, the series treatment setup resulted in nearly complete removal efficiency, approximately 100%, for Fat, Oil, and Grease, turbidity, and total suspended solids in the wastewater samples. The treatment setup using only wheat straw achieved removal efficiencies between 41.3% and 83.3%, whereas the setup using only pistachio shell achieved removal efficiencies ranging from 43.3% to 89.1%. Statistical analyses confirmed the significance of observed differences, with isotherm and kinetic models providing valuable insights into adsorption characteristics. Freundlich constants ranged from 3.6 to 12.38, Moreover, the integrated treatments consistently outperformed individual ones, as demonstrated by Water Quality Index values. The Water Quality Index values ranged from 2114.26 for raw wastewater, classified as “unsuitable for drinking,” to 154.47 for the series connection of wheat straw and pistachio shell, indicating a significant improvement in water quality.