Effect of pH, Salinity, Dye, and Biomass Concentration on Decolourization of Azo Dye Methyl Orange in Denitrifying Conditions

Abstract

A recent study by the current authors found simultaneous decolourization and mineralization of high concentrations of methyl orange (500 mg/L) in an anoxic up-flow reactor in denitrifying conditions. To supplement this work, various batch reactor studies were carried out to study the effect of (i) pH (4 to 9), (ii) salinity (1 g/L NaCl to 10 g/L NaCl), (iii) dye concentration (100 mg/L to 1000 mg/L), (iv) biomass concentration (0.3 g/L to 0.21 g/L); on the process, and (iv) kinetics of decolourization in denitrifying conditions. The adapted mixed microbial consortium, originally sourced from the activated sludge process, was capable to simultaneously remove colour, COD, and NO3−-N under denitrifying conditions, even at high methyl orange (MO) concentrations of 1000 mg/L at 84 h. Although the decolourization was possible for wide ranges of pH, better performance was obtained at alkaline pH levels. The decolourization performance increased when biomass concentration increased and was not affected by salinity up to 10 g/L NaCl. This may have been due to enhanced lyses of biomass at high salt concentrations. Batch kinetic studies showed that the MO decolourization followed first-order kinetics, with a rate constant of 0.0612 h−1. Results of this study may help in the future application of textile effluent treatments, using a high biomass retention reactor in denitrifying conditions with minimum sludge disposal costs.

Spectral Analysis of the Degradation of the Reactive Black 5 Dye Using Newly Developed Advanced Oxidation Process

“…At the same time, the rate declined at the highest concentration of the RB5 (Fig. 1 ), which is similar to the reports of Trivedi et al [13] that at higher concentrations of methylene orange (MO), the low decolourization was observed (Fig. 2).…”

“…AOP uses progressive oxidation technologies to decompose complex organic compounds, such as dyes and pigments, into harmless carbon dioxide and water [2]. Most AOP consists of the generation of highly reactive OH radicals, which are powerful oxidizing species that have the ability to mineralize organic pollutants or convert them into less harmful sludge [9][10][11][12][13][14][15]. Several AOP methods are available, generating *OH radicals, including both non-photochemical and photochemical methods like Ozonation, Ozonation at elevated pH (> 8.5) Ozone + hydrogen peroxide (O 3 /H 2 O 2 ), Ozone + catalyst (O 3 /CAT), Fenton system (H 2 O 2 /Fe 2 + ), O 3 /UV, H 2 O 2 /UV, O 3 /H 2 O 2 /UV, Photo-Fenton/Fenton-like systems [15][16][17][18][19][20][21][22].…”

“…While KMnO 4 alone showed effective decolouration at a very low pH, it had limited application due to this pH (5). Potassium permanganate is famous as an oxidizing agent, an odourless, water-soluble solid with purple crystals where Mn (VII) is converted into Mn(II) with a 5e system [12][13][14][15]. Hydrogen peroxide is another oxidizing agent used in this research to control the hazardous effects of dye additive urea, a fixer of dye used during the textile dye process.…”