Optimising Batch Sorption: Effect of Mixing Speed and Reactor Design on Wastewater Treatment Kinetics and Efficiency

The batch sorption process is used to remove various species from wastewater and can be optimised by selecting adequate process parameters and reactor geometry. As sorption is a heterogeneous process, achieving the desired process outcomes in a batch reactor relies heavily on establishing conditions in which the influence of interphase diffusion is minimised while keeping the efficiency and cost of the process at acceptable values. These conditions can be managed by the selection of appropriate reactor geometries and mixing speed through examination of their influence on the sorption yield and cost. The relationship between mixing speed and power consumption is important, as excessive mixing can lead to increased energy costs without proportional gains in sorption kinetics and efficiency. For these reasons, the effect of reactor geometry and mixing speed on copper sorption kinetics, efficiency, and energy consumption was studied. The Ritchie model and Mixed surface reaction and diffusion-controlled sorption kinetic model were employed for the kinetic study. CFD simulations were carried out to identify optimal designs that enhance process efficiency and reduce energy consumption. Data obtained indicate that the sorption process generally follows second-order kinetics. Results demonstrate that sorption can be effectively conducted at impeller speeds lower than the critical suspension speed (NJS), achieving almost equal removal efficiencies (after 30 min) while reducing energy consumption. From the perspective of energy consumption, reactors without baffles are a significantly better solution than baffled reactors, especially when using a PBT impeller. From a kinetic standpoint, better results are achieved at the highest N/NJS or NJS. In baffled reactors, considering both power consumption and process duration, the SBT impeller emerges as the most efficient choice. Considering the compromises between power consumption and process duration the choice of reactor geometry and specific operating conditions should align with process priorities, such as energy savings through lower power consumption or reduced mixing time. FTIR spectra did not reveal the differences in the zeolite structure after the sorption process occurred.