Novel AOPs-Based Dual-Environmental Digestion Method for Determination of Total Dissolved Nitrogen in Water

Abstract

Based on a synergistic digestion method of ultraviolet combined with ozone (UV/O3), this article investigates the reaction characteristics of nitrogen-containing compounds (N-compounds) in water and the influence of ions on digestion efficiency. In this respect, a novel and efficient AOPs-based dual-environmental digestion method for the determination of total dissolved nitrogen (TDN) in waters with complex components is proposed, in the hopes of improving the detection efficiency and accuracy of total nitrogen via online monitoring. The results show that inorganic and organic N-compounds have higher conversion rates in alkaline and acidic conditions, respectively. Meanwhile, the experimental results on the influence of Cl−, CO32−, and HCO3− on the digestion process indicate that Cl− can convert to radical reactive halogen species (RHS) in order to promote digestion efficiency, but CO32− and HCO3− cause a cyclic reaction consuming numerous •OH, weakening the digestion efficiency. Ultimately, to verify the effectiveness of this novel digestion method, total dissolved nitrogen samples containing ammonium chloride, urea, and glycine in different proportions were digested under the optimal conditions: flow rate, 0.6 L/min; reaction temperature, 40 °C; pH in acidic conditions, 2; digestion time in acidic condition, 10 min; pH in alkaline conditions, 11; digestion time in alkaline conditions, 10 min. The conversion rate (CR) of samples varied from 93.23% to 98.64%; the mean CR was greater than 95.30%. This novel and efficient digestion method represents a potential alternative for the digestion of N-compounds in the routine analysis or online monitoring of water quality.

Oxidative digestion of dissolved N‐compounds by the UV/O3 process: Kinetic models and rate constants

“…Therefore, the empirical constant R ct 36 is introduced to simplify the equation defined as Equation ( 20) obtained from engineering experiments representing the rate of the time integral of [•OH] to the time integral of [O 3 ] in the closed reaction system from the beginning to the end of the reaction. Parameter t in Equation (20) represents the reaction time.…”

“…The time integral of [O 3 ] can be obtained by measuring the [O 3 ] in solution at a fixed time interval, and then fitting the curve of [O 3 ] ∼ 𝑡 to obtain the corresponding integral area. Equation ( 22) is obtained by taking Equation (20) into Equation (19). 36 The second-order reaction kinetic equation of p-CBA with •OH is shown in Equations ( 23)- (24).…”

“…Advanced oxidation processes (AOPs) based on •OH radical digesting N-compounds in water mostly include ozone oxidation, 12 UV/O 3 , 13,14 UV/H 2 O 2 , 15,16 Fenton, 17 and TiO 2 photocatalysis, 18,19 etc. Sun et al 20 selected nitrate as the target digestion product according to the stability of different products (nitrate, nitrite, ammonia, and NO 2 *) and studied the digestion efficiency of DIN and DON in different pH environment based on UV/O 3 synergetic digestion method which showed that DIN and DON have the higher conversion rate in alkaline (pH 11) and acidic (pH 2) condition, respectively. In this study, we would explore the digestion mechanisms and measure the rate constants under the optimum digestion conditions proposed by Sun et al…”