Mineralization and biodegradability enhancement of hazardous organic compounds using conventional and modified fenton's reagents

Abstract

Enhancement on mineralization and biodegradability of hazardous organic compounds could be performed by conventional or modified Fenton's reaction. The degree of mineralization was measured by dissolved organic carbon (DOC) while the biodegradability was quantified by biodegradable DOC (BDOC)/DOC ratio. Four hazardous organic compounds were tested including trichloroethene (TCE), 2,4-dichlorophernol (2,4-DCP), 1,4-dioxane (1,4-D) and 1,2,3-trichloropropane (TCP) solutions. Three types of iron catalyst of ferrous ion (Fe[superscript +2]), ferric ion (Fe[superscript +3]) and zero-valence iron (Fe[superscript 0]) were investigated. Three different types of iron: H[subscript 2]O[subscript 2] :DOC of 5:10:1, 10:20:1 and 10:20:1 on mass basis and pH of 2,3 and 4 were tested to identify the conditions that maximized DOC elimination, biodegradability increase and DOC elimination plus the biodegradability increase of water samples. The results showed that the conditions for the highest DOC reduction were not necessary to be the same as the conditions of the largest biodegradability increase. Similarly, the optimum conditions for different compounds solution on mineralization and biodegradability enhancement were not necessary to be the same. Generally, the optimum conditions for combination of DOC elimination and biodegradability increase observed as the ratio of iron (Fe[superscript +2] and Fe[superscript 0]): H[subscript 2]O[subscript 2] :DOC were 10:20:1, except Fe[superscript +2] :H[subscript 2]O[subscript 2] :DOC for TCP as 10:10:1. Initial pH exerted small effect on mineralization and biodegradability of 4 compounds. More than 90% of total DOC reduction and biodegradability i ncrease were almost found in 120 and 60 minutes, respectively. The pseudo-first order and second order were found the best fit for mineralization reaction rate while zero order was considered as the biodegradability reaction rate. The oxidation by-products for each organic compound were identified by GC/MS analysis. The results show that the by-products of Fe 0 in Fenton's reaction were not similar to the by-products of Fe[superscript +2] and Fe[superscript +3] according to the different mechanisms as for reduction and oxidation for Fe[superscript 0] while only oxidation for Fe[superscript +2] and Fe[superscript +3] , respectively.