Bicarbonate Effect in the Ozone-UV Process in the Presence of Nitrate (original) (raw)
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Journal of Water Process Engineering, 2021
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This study was designed to investigate the reaction mechanisms of oxidation of various phenolic compounds by ozone and ozone + U.V. radiation at pH 2.5, 7.0 and 9.0. Experimental results indicated that the molecular ozone is the predominant oxidant only at acidic pH; at neutral and basic pH, in the absence or presence of U.V. radiation, free radical reaction is the major pathway in the oxidation of phenolic compounds. The overall removal of phenols and the removal of TOC increase with increasing pH during ozonation with or without U.V. light. For a specific pH, the removal rates of phenol and TOC are highest for ozone + U.V. light followed by ozone and then U.V. light alone.
Water Research, 1997
The oxidation of two wastewaters with ozone combined with hydrogen peroxide or UV radiation (2~;4 nm) has been studied. The oxidation yields of these systems were compared with those from ozonation alone at similar experimental conditions. It was found that O3/H202 oxidation leads to important increases in COD degradation rate (i.e. 86% at pH 6 in tomato wastewaters). The differences between the oxidation types (03 and O3/H202) diminish with increase in pH. With distillery wastewaters the presence of hydrogen peroxide hardly increases the oxidation rate. However, the combination of O3/UV radiation was the best oxidation method applied because of the improvements achieved in both COD and TOC disappearance rates compared to those of ozonation alone, regardless of wastewater type treated. As happened with other oxidation systems, the COD and TOC reductions were higher in tomato wastewater oxidation. Different kinetic parameters were also determined in order to quantify the reactivity of wastewaters towards the oxidation systems applied. © 1997 Elsevier Science Ltd
Oxidative degradation of N-Nitrosopyrrolidine by the ozone/UV process: Kinetics and pathways
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N-Nitrosopyrrolidine (NPYR) is an emerging contaminant in drinking water and wastewater. The degradation kinetics and mechanisms of NPYR degradation by the O3/UV process were investigated and compared with those of UV direct photolysis and ozonation. A synergistic effect of ozone and UV was observed in the degradation of NPYR due to the accelerated production of OH• by ozone photolysis. This effect was more pronounced at higher ozone dosages. The second-order rate constants of NPYR reacting with OH• and ozone was determined to be 1.38 (± 0.05) × 10(9) M(-1) s(-1) and 0.31 (± 0.02) M(-1) s(-1), respectively. The quantum yield by direct UV photolysis was 0.3 (± 0.01). An empirical model using Rct (the ratio of the exposure of OH• to that of ozone) was established for NPYR degradation in treated drinking water and showed that the contributions of direct UV photolysis and OH• oxidation on NPYR degradation were both significant. As the reaction proceeded, the contribution by OH• became l...
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Comparison of advanced oxidation processes (AOPs) can be difficult due to physical and chemical differences in the fundamental processes used to produce d OH radicals. This study compares the ability of several AOPs, including ozone, ozone+H 2 O 2 , low pressure UV (LP)+H 2 O 2 , and medium pressure UV (MP)+H 2 O 2 in terms of energy required to produce d OH radicals. Bench scale d OH radical formation data was generated for each AOP using parachlorobenzoic acid (pCBA) as an d OH radical probe compound in three waters, Lake Greifensee water, Lake Zurich water, and a simulated groundwater. Ozone-based AOPs were found to be more energy efficient than the UV/H 2 O 2 process at all H 2 O 2 levels, and the addition of H 2 O 2 in equimolar concentration resulted in 35% greater energy consumption over the ozone only process. Interestingly, the relatively high UV/AOP operational costs were due almost exclusively to the cost of hydrogen peroxide while the UV portion of the UV/AOP process typically accounted for less than 10 percent of the UV/AOP cost and was always less than the ozone energy cost. As the d OH radical exposure increased, the energy gap between UV/H 2 O 2 AOP and ozone processes decreased, becoming negligible in some water quality scenarios.
Ozone oxidation of compounds resistant to biological degradation
Water Research, 1991
The ozonation of a polyethoxylated nonyl phenol was carried out under different conditions of pH, reaction time and iron ion added. Analysis of the reaction products was performed using RP-HPLC, NP-HPLC and MS-FAB and the degradation of the polyethoxylated side chain to give a phenol was monitored. Several experiments of ozonation of different substituted phenols and widespread cinnamic acids are reported. Their degradation was monitored by u.v. measurements. Some mechanistic considerations are derived from these data.