Tropical Agricultural Machinery Research Institute

Pharmaceutical residues, especially non-steroidal anti-inflammatory drugs (NSAIDs), are emerging contaminants that hinder sustainable water management and limit wastewater upcycling. In this work, we address the challenge of wastewater upcycling via the scale-up of a hybrid advanced oxidation process (AOP) that couples hydrodynamic cavitation (HC) and non-thermal electrical discharge (ED) plasma, and that will enable the in situ generation of ROS. In order to demonstrate process scalability, the hybrid HC/ED plasma system was initially validated at pilot scale (600 L h-1) and subsequently up-scaled to a semi-industrial reactor (3200 L h-1), specifically designed starting from the pilot unit. The effective exploitation of HC/ED plasma synergy led to the process achieving the quantitative degradation of model pollutants, specifically ibuprofen and diclofenac (10 mg/L), in competitive times (13 passes) and without detectable byproducts, thereby validating the process' robustness and successful scale-up. Although current wastewater treatment plants (WWTPs) recover nutrients from sludge, biologically treated effluents still contain pharmaceutical residues. This work therefore, potentially solves this issue by providing a sustainable strategy for complete wastewater upcycling in WWTPs, delivering safe regenerated water for agricultural and irrigation reuse, while closing the water cycle.

Lateritic soils in tropical regions feature cohesive textures and high specific resistance, driving up energy demands for tillage and harvesting machinery. However, current equipment designs lack discrete element models that account for soil moisture variations, and the microscopic effects of water content on lateritic soil deformation remain poorly understood. This study aims to calibrate and validate discrete element method (DEM) models of lateritic soil at varying moisture contents of 20.51%, 22.39%, 24.53%, 26.28%, and 28.04% by integrating the Hertz–Mindlin contact mechanics with bonding and JKR cohesion models. Key parameters in the simulations were calibrated through systematic experimentation. Using Plackett–Burman design, critical factors significantly affecting axial compressive force—including surface energy, normal bond stiffness, and tangential bond stiffness—were identified. Subsequently, Box–Behnken response surface methodology was employed to optimize these parameters by minimizing deviations between simulated and experimental maximum axial compressive forces under each moisture condition. The calibrated models demonstrated high fidelity, with average relative errors of 4.53%, 3.36%, 3.05%, 3.32%, and 7.60% for uniaxial compression simulations across the five moisture levels. Stress–strain analysis under axial loading revealed that at a given surface displacement, both fracture dimensions and stress transfer rates decreased progressively with increasing moisture content. These findings elucidate the moisture-dependent micromechanical behavior of lateritic soil and provide critical data support for DEM-based design optimization of soil-engaging agricultural implements in tropical environments.