Monitoring of the total carbon and nitrogen balance during the mineralization of nitrogen containing compounds by heat activated persulfate

Abstract

Peroxydisulfate (S2O82−) is widely applied in environmental remediation and water treatment as an agent for the unselective oxidation of organic contaminants. S2O82− itself is a strong oxidation agent but activation by heat, UV radiation, or metal catalysts forms sulfate radicals (SO4−), which offer a higher oxidation potential and faster reaction kinetics. The mechanism of degradation for many organic contaminants by sulfate radicals is well studied, but the final mineralization products are not commonly evaluated. Nitrogen containing compounds are known to produce different mineralization products depending on their structure and the reaction conditions. For the identification of the main mineralization products, two approaches for the determination of nitrogen mass balances were evaluated. The first approach was based on a combination of total organic carbon (TOC), and total nitrogen bound (TNb). The second approach used a combination of TOC and ion chromatography (IC). The evaluation based on the TOC and TNb by high temperature combustion was found to be significantly biased as measured ammonium concentrations were underestimated by the TNb measurements in the presence of peroxydisulfate. With the TOC/TNb method, 83.2 ± 1.1% of the initial nitrogen could be recovered after the oxidation. The TOC/IC based approach led to an overall recovery of 91.1 ± 1.4%, where NO3− and NH4+ were identified as the main products. Based on the fraction of ammonium provided by the IC measurements, the TOC/TNb based results could be corrected for the underestimation of ammonium which led to a recovery of 95.9 ± 3.1%. The presented methods are applicable for the determination of nitrogen mass balances in lab-scale studies, as well as for the monitoring of mineralization products in field applications.