Abstract
We report results of investigating the processes of electrochemical oxidation of ammonium in a two-chamber electrolyzer depending on the composition of the original solutions ‒ anolyte and catholyte, current density, electrolysis duration. It is shown that the electrochemical oxidation of ammonia in aqueous solutions of ammonium sulfate proceeds at a rate of 14‒55 mg/(dm 3 ·hours) at a current density of 86.2‒172.4 A/m 2 and the starting concentrations of a given ion of 10‒120 mg/dm 3 . The rate of ammonium oxidation under these conditions increases with increasing starting concentrations of ammonium and with increasing current density. The output of oxidized ammonium for current and specific consumption of electricity for water purification from ammonium are defined based on ammonium concentrations and current density and increase with an increase in the concentration of a given ion and a decrease in current density. Ammonium oxidation rate increases by 1.66 times in solutions of ammonium sulfate ([NH 4 + ]=90 mg/dm 3 , j=172.4 A/m 3 ) in tap water, compared with distilled water. This is due to the presence of chlorides in tap water, which act as a catalyst during ammonium oxidation at the expense of the intermediate formation of active chlorine. Under these conditions, we observed complete oxidation of ammonia compared with solutions on distilled water where the residual ammonium concentrations reach 1‒3 mg/dm 3 . It is shown that the presence of chlorides in catholyte at a concentration of 30 mg/dm 3 almost does not accelerate the oxidation of ammonium. Our work demonstrated thatекек in all cases, during oxidation of ammonium, pH of solutions decreases to 6.1‒2.0, which is predetermined by the oxidation of ammonium to nitrates and the acidification of water by the formed nitric and sulphuric acids. Based on the reported results, it can be concluded that the electrochemical method is the most promising method for the extraction of ammonium ions from water. Its application makes it possible to achieve a 100 % water purification.
Highlights
Nitrogen-containing compounds in surface waters are in the dissolved, colloidal, and suspended state
It is known that in the presence of chlorides in anolyte there is the formation of active chlorine, which affects the process of ammonium oxidation
It is shown that the efficiency of electrochemical oxidation of ammonium in solutions of ammonium sulfate in the anode region of a two-chamber electrolyzer depends both on the concentrations of ammonium and current density
Summary
Nitrogen-containing compounds in surface waters are in the dissolved, colloidal, and suspended state. The concentration of ammonium ions in non-contaminated surface waters is negligible and varies in the range of 10–200 mg/dm (recalculated for nitrogen) The presence of these ions in water is explained by the processes of biochemi cal degradation of protein substances, deamination of amino acids, decomposition of urea under the action of urease. The elevated content of ammonium ions in water can serve the indicator that points to the deterioration in the state of natural waters under the influence of anthropogenic load. Based on the requirements from the World Health Organization, the concentration of ammonium ions in drinking water is not standardized as the harmful effect of a given ion on human health is not determined It is noted, that its content exceeding 1.5 mg/dm worsens the smell of water, and at concentrations larger than 35 mg/dm there is deterioration in the taste of water. At the first stage, this involves the selection of a method for purification, and at the second stage – establishing the optimal parameters for purification processes
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