Treatment of synthetic urine by electrochemical oxidation using conductive-diamond anodes

Abstract

In this work, the electrochemical oxidation of synthetic urine by anodic oxidation using boron-doped diamond as anode and stainless steel as cathode was investigated. Results show that complete depletion of chemical oxygen demand (COD) and total organic carbon (TOC) can be attained regardless of the current density applied in the range 20–100 mA cm−2. Oxalic and oxamic acids, and, in lower concentrations, creatol and guanidine were identified as the main intermediates. Chloride ions play a very important role as mediators and contribute not only to obtain a high efficiency in the removal of the organics but also to obtain an efficient removal of nitrogen by the transformation of the various raw nitrogen species into gaseous nitrogen through chloramine formation. The main drawback of the technology is the formation of chlorates and perchlorates as final chlorine products. The increase of current density from 20 to 60 mA cm−2 led to an increase in the rate of COD and TOC removals although the process becomes less efficient in terms of energy consumption (removals of COD and TOC after applying 18 Ah dm−3 were 93.94 and 94.94 %, respectively, at 20 mA cm−2 and 89.17 and 86.72 %, respectively, at 60 mA cm−2). The most efficient conditions are low current densities and high temperature reaching total mineralization at an applied charge as low as 20 kAh m−3. This result confirmed that the electrolysis using diamond anodes is a very interesting technology for the treatment of urine.