Dark Fenton process which is frequently employed in treating non-biodegradable organics in wastewater uses ferrous or ferric ion to produce OH radical from hydrogen peroxide. Since the decomposition rate of hydrogen peroxide determines the formation rate of OH radical which is a key compound in Advance Oxidation Process, it is important to improve the current understanding of the Fenton chemistry affecting the decomposition rate of hydrogen peroxide under the presence of various inorganic/organic elements in aqueous conditions. Many researches which investigated the influence of inorganic/organic elements on Fenton chemistry were more focused on the behavior of target compounds not hydrogen peroxide (Ming-Chun Lu et.al., 1997; Kiwi et.al, 2000; and Pignatello, 1992). The effects of organic or inorganic compounds on hydrogen peroxide decomposition were not well defined. This study was attempted to investigate the effects of various organic or inorganic compounds on the decomposition rate of hydrogen peroxide in dark Fenton reaction. Most of the experiments were conducted in excess presence of hydrogen peroxide over ferric ion (≈100) in the following conditions: [H_2O_2]_0 ≈ 100 mM, [Fe~(3+)]_0 = 1mM, pH_0 = 2.8, temp.= 20 ～ 22°C. Inorganic/organic elements of interest in this study are classified into several groups; (1) perchlorate (C1O_4~-), nitrate (NO_3~-), sulfate (SO_4~(2-)), and chloride (C1~-) as the anions of iron salt, (2) EDTA (ethylene diamine tetra acetic acid), oxalate and phosphate (also often used as a buffer) as a well known complex forming agent, (3) tertiary butanol as a well known OH radical scavenger, (4) phenol and p-chloro phenol as a model compound of synthetic organic chemicals, (5) methanol and acetic acid which are frequently encountered in biologically treated wastewater. The results of inorganic/organic elements affecting hydrogen peroxide decomposition rate were expressed as the observed rate constants of pseudo-first order decay kinetics of hydrogen peroxide as a function of the concentration of inorganic/organic elements (Figure 1). The assumption of pseudo-first order decay kinetics of hydrogen peroxide under the given experimental conditions was reasonable (R~2 > 0.99).
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