Treatment of landfill leachate by an ultrasonic-three-dimensional electrode coupled reaction system

Abstract

Advanced oxidation technology has an excellent treatment effect on refractory wastewater. In this study, conventional, unmodified, and low-cost electrode materials were used to construct an ultrasonic three-dimensional electrode coupled reaction system (US-3DES), and its effectiveness in treating leachate from a closed municipal solid waste landfill was investigated. The results showed that, under the optimal treatment conditions, the COD and UV₂₅₄ removal rates were 98.15% and 96.32%, respectively, after 120 min of reaction. This performance significantly surpassed that of single ultrasound (US) (COD and UV₂₅₄ removal rates of 53.13% and 60.74%, respectively) and a single three-dimensional electrode system (3DES) (73.84% and 87.57%, respectively). Kinetic analysis showed that the reaction process exhibited the characteristics of a pseudo-first-order reaction in two stages. The calculated synergistic indices (SI₁ = 1.26, SI₂ = 9) demonstrated a significant synergistic effect in the coupled system. Free radicals in the coupled reaction system were detected by methylene blue spectrophotometry, and the results showed that hydroxyl radical concentration [·OH] reached up to 9.8×10^-6 M. The steady-state free radical generation rates in the two kinetic stages were 9.7×10⁻⁹ M s⁻¹ and 2.67×10⁻⁸ M s⁻¹, respectively. The energy consumption and treatment cost of US-3DES were 149.0 kWh·kg COD⁻¹ and 25,021.1 CNY·kg COD⁻¹, respectively. This study confirms that US-3DES offers the following benefits: efficient leachate treatment, simple operation, low cost, and no requirement of additional chemicals. Additionally, it provides feasible solutions for the engineering applications of refractory wastewater treatment.