Sustainable pretreatment and adsorption of chemical oxygen demand from car wash wastewater using Noug sawdust activated carbon

Abstract

Wastewater treatment in developing countries remains inadequate due to limited awareness of its environmental and health impacts, coupled with the high costs of available treatment technologies. Therefore, developing cost-effective, accessible, and efficient treatment solutions is crucial for protecting public health and the environment. This study evaluates the chemical oxygen demand (COD) removal efficiency of a novel combined pre-treatment process followed by adsorption using Noug sawdust activated carbon (NSDAC), a low-cost and sustainable adsorbent. A laboratory-based study was conducted to optimize COD removal efficiency through sequential pre-treatment steps as screening, sedimentation, and filtration followed by adsorption with NSDAC. The adsorbent was chemically activated using sulfuric acid (H₂SO₄) and thoroughly characterized to assess its physicochemical properties. Batch adsorption experiments examined the influence of pH, adsorbent dose, contact time, and agitation speed on COD removal efficiency. A central composite design was employed to evaluate process interactions and optimize conditions using Design Expert version 13.0.5.0 software. ANOVA and a quadratic logistic regression model were used to assess the statistical significance of process parameters. The highest COD removal efficiency (90.53%) was achieved at a pH of 6.05, an adsorbent dose of 10.87 g/L, a contact time of 86.94 min, and an agitation speed of 190.31 rpm. When applied to real wastewater, the integrated pre-treatment and NSDAC adsorption system achieved a COD removal efficiency of 97.50%, demonstrating superior performance. Adsorption data best fit the Langmuir isotherm model (R² = 0.9993) and followed pseudo-second-order kinetics (R² = 0.9936), indicating monolayer adsorption and chemisorption as the dominant mechanism. This study highlights the potential of NSDAC as a sustainable alternative to conventional adsorbents, contributing to the development of cost-effective wastewater treatment technologies. Future research should focus on optimizing large-scale applications, assessing the economic feasibility of widespread NSDAC adoption, and investigating its regeneration and reusability to improve long-term sustainability.