Advanced Oxidation Processes (AOPs) for Waste Water Treatment

Abstract

Advanced Oxidation Processes refers to a set of chemical treatment procedures designed to remove organic and inorganic materials in waste water by oxidation. One such type of process is called In Situ Chemical Oxidation. Contaminants are oxidized by four different reagents: ozone, hydrogen peroxide, oxygen, and air, in precise, preprogrammed dosages, sequences, and combinations. These procedures may also be combined with UV irradiation and specific catalysts. This results in the development of hydroxyl radicals. A well-known example of AOP is the use of Fenton’s reagent. The AOP procedure is particularly useful for cleaning biologically toxic or non-degradable materials such as aromatics, pesticides, petroleum constituents, and volatile organic compounds in waste water. The contaminant materials are converted to a large extent into stable inorganic compounds such as water, carbon dioxide and salts, i.e. they undergo mineralization. A goal of the waste water purification by means of AOP procedures is the reduction of the chemical contaminants and the toxicity to such an extent that the cleaned waste water may be reintroduced into receiving streams or, at least, into a conventional sewage treatment. This report presents a general review of efficient advanced oxidation processes developed to decolorize and/or degrade organic pollutants for environmental protection. Fundamentals and main applications of typical methods such as fenton, electro-fenton, photo-fenton, ozonation and UV radiation was discussed. Various combination of this processes and there industrial applications are also shown in the study. Ozonation is emerging as a potential process for color removal of dyes, since the chromophore groups with conjugated double bonds, which are responsible for color can be broken down by ozone either directly or indirectly forming smaller molecules, thereby decreasing the color of the effluents. Ozonation and its combinations like, O3+UV, O3+Fenton Process, O3+Catalyst, O3+Electrofenton Process, O3+H2O2 ect., are effective for waste water treatment. The present study demonstrated that nearly complete decolorization of RB 5 and RR 135 could be accomplished by ozonation. The time required for the complete decolorization gradually increase with increase in the initial dye concentration. For RR135 after 48, 55 and 67 min reaction time, complete decolorizaton was achieved at initial dye concentrations of 500, 1000 and 1500 mg/L, respectively. For RB5 after 65, 130 and 165 min reaction time, complete decolorizaton was achieved at initial dye concentrations of 500, 1000 and 1500 mg/L, respectively. The COD removal efficiency gradually decreased with an increase in the initial concentration. For RR135 after 60, 65 and 87 min reaction time, the COD removal percentage was 66.66%, 61% and 56.64% at initial dye concentrations of 500, 1000 and 1500 mg/L, respectively. For RB5 after 65, 150 and 140 min reaction time, the COD removal percentage was 50%, 39.47% and 28.09% at initial dye concentrations of 500, 1000 and 1500 mg/L, respectively.