Energy consumption and reaction rate optimization combining turbulence promoter and current modulation for electrochemical mineralization

Abstract

In the current world scenario, one of the environmental and public health problems that still needs a more efficient intervention is the pollution caused by industrial effluents containing toxic organic compounds, typically treated by biological processes. However, this method is inefficient for the degradation of biorefractory compounds, in addition to generating a large amount of sludge and requiring a larger physical area. Due to these factors, electrochemical techniques have stood out as a promising treatment alternative, mainly for their efficiency and environmental compatibility. However, the energy consumption of the process still represents a factor to be improved for its effective application. In this sense, two strategies were approached in this study to overcome this problem. Current modulation is one of them and consists of controlling the applied current so that its value is always close to the limiting value. Using this technique, it is possible to improve the mineralization efficiency and consequently reduce energy consumption; however, there is the drawback that the processing time becomes longer. Considering this, the second proposed strategy consisted of the use of turbulence promoters (TPs) to increase the mass transfer in the system, also contributing to the reaction kinetics and thus, reducing the electrooxidation time. In this way, the time increase due to the application of modulated current (MC) can be compensated, maintaining the efficiency of the process. In this context, this work aimed to optimize the electrooxidation process by combining current modulation with TPs to simultaneously improve energy consumption and mineralization time. Phenol was used as a model molecule in this study and its electrooxidation was evaluated in an electrochemical flow reactor, using the boron-doped diamond anode (BDD). The plastic mesh turbulence promoter (MTP) and reticulated vitreous carbon (RVC) were evaluated. The combined approach enabled the reduction of the energy consumption from 168 ±31 kWh per kg of total organic carbon (TOC) (galvanostatic mode) to 72 ±6 kWh kg-1 TOC (modulated current + MTP). Additionally, considering 75% TOC removal, the use of turbulence promoters allowed a reduction in electrolysis time from 420 min to 295 min (~ 30%) in the processes applying MC. Under galvanostatic conditions and mass transfer control regime, the use of RVC as turbulence promoter outperformed the mineralization performance observed using the MTP, mainly due to its porous matrix. However, the variation in the type of promoter had less influence on electrolysis under current modulation conditions, with similar efficiency observed at low flow velocities. The results reinforced the potential of electrooxidation for the treatment of effluents, paving the way for obtaining a process with rapid degradation kinetics and high mineralization efficiency, resulting in low energy consumption.