The performance of three typical single and two coupled electrochemical processes for drilling wastewater treatment：comparison and implication

Electrochemical processes, especially for anode and cathode coupling processes, are promising and energy efficient for wastewater treatment. In this study, three single processes (electrocoagulation (EC), electro-catalytic oxidation (ECO), and E-peroxone) and their corresponding anode and cathode coupling processes (EC coupled with E-peroxone (ECP) and ECO coupled with E-peroxone (ECOP)) were employed for drilling wastewater treatment. Under similar current density, removal efficiency and first order kinetic constant for the single process followed the orders of EC > E-peroxone > ECO. The coupled ECP process had higher removal efficiency and current efficiency than that of coupled ECOP process. However, the removal efficiency and current efficiency for coupled ECP process were only slightly higher than that of EC process with the synergistic factor for COD removal of 0.78 for ECP process, indicating the poor synergistic effect for drilling wastewater treatment and negligible assistance of oxidation for coagulation, which was also verified by a process-based model. The EC process might play a dominant role in the ECP process for drilling wastewater treatment. Alternatively, these results provide us a clue that the EC process as a pretreatment process might significantly improve the treatment efficiency for the subsequent E-peroxone process, which was also implied by the experimental results and kinetic constants for the sequential EC–E-peroxone process. This study also highlights that a single, coupled, and sequential process should be adopted according to water quality and components of the wastewater to achieve high removal efficiency and current efficiency.