Carmen S.D. Rodrigues

Treatment of textile effluent by chemical (Fenton's Reagent) and biological (sequencing batch reactor) oxidation.

The removal of organic compounds and colour from a synthetic effluent simulating a cotton dyeing wastewater was evaluated by using a combined process of Fentons Reagent oxidation and biological degradation in a sequencing batch reactor (SBR). The experimental design methodology was first applied to the chemical oxidation process in order to determine the values of temperature, ferrous ion concentration and hydrogen peroxide concentration that maximize dissolved organic carbon (DOC) and colour removals and increase the effluents biodegradability. Additional studies on the biological oxidation (SBR) of the raw and previously submitted to Fentons oxidation effluent had been performed during 15 cycles (i.e., up to steady-state conditions), each one with the duration of 11.5h; Fentons oxidation was performed either in conditions that maximize the colour removal or the increase in the biodegradability. The obtained results allowed concluding that the combination of the two treatment processes provides much better removals of DOC, BOD(5) and colour than the biological or chemical treatment alone. Moreover, the removal of organic matter in the integrated process is particularly effective when Fentons pre-oxidation is carried out under conditions that promote the maximum increase in wastewater biodegradability.

Optimization of the azo dye Procion Red H-EXL degradation by Fenton's reagent using experimental design.

Chemical oxidation by Fentons reagent of a reactive azo dye (Procion Deep Red H-EXL gran) solution has been optimized making use of the experimental design methodology. The variables considered for the oxidative process optimization were the temperature and the initial concentrations of hydrogen peroxide and ferrous ion, for a dye concentration of 100mg/L at pH 3.5, the latter being fixed after some preliminary runs. Experiments were carried out according to a central composite design approach. The methodology employed allowed to evaluate and identify the effects and interactions of the considered variables with statistical meaning in the process response, i.e., in the total organic carbon (TOC) reduction after 120 min of reaction. A quadratic model with good adherence to the experimental data in the domain analysed was developed, which was used to plot the response surface curves and to perform process optimization. It was concluded that temperature and ferrous ion concentration are the only variables that affect TOC removal, and due to the cross-interactions, the effect of each variable depends on the value of the other one, thus affecting positively or negatively the process response.

Treatment of textile dye wastewaters using ferrous sulphate in a chemical coagulation/flocculation process

The coagulation/flocculation treatment using FeSO4·7H2O as a coagulant is evaluated in this work for the removal of organic compounds and colour from synthetic effluents simulating the cotton, acrylic and polyester dyeing wastewaters. The coagulant dose, temperature, pH, stirring speed and stirring time that maximized the removal of dissolved organic carbon (DOC) and colour for each effluent are determined for the coagulation process. The effect of the stirring speed, stirring time and the dose of flocculant (Magnafloc 155 or Superfloc C-573) on the flocculation stage is also evaluated for effluents pretreated by coagulation at the optimal conditions previously determined. The obtained results showed that the optimal operating conditions are different for each effluent, and the process (coagulation/flocculation) as a whole was efficient in terms of colour removal (∼91% for cotton, ∼94% for acrylic effluents; polyester effluent is practically colourless). However, the DOC removal observed is not significant (∼33% for polyester, ∼45% for cotton and ∼28% for acrylic effluents). On the other hand, the remaining dissolved iron content is appropriate for further integrating the treatment with an iron-catalysed Fenton process, thus reducing the consumption of chemicals in the overall treatment.

Technical and economic feasibility of polyester dyeing wastewater treatment by coagulation/flocculation and Fenton's oxidation

This study aims to investigate the efficiency of individual and integrated processes applied to organic matter abatement and biodegradability improvement of a polyester dyeing wastewater, namely coagulation/flocculation combined with Fentons reagent (Approach 1), Fenton oxidation alone (Approach 2) and its integration with coagulation/flocculation (Approach 3). The effects of Fe2+ dose, initial concentration of the oxidant (H2O2) and temperature during Fentons oxidation were evaluated in Approaches 1 and 2, whereas in Approach 3 the influence of pH and flocculant dose was also assessed, during the coagulation/flocculation stage. Toxicity and biodegradability of the final effluent were also evaluated. After oxidation, a slight increase in the specific oxygen uptake rate of the effluent was observed (from 27.0 up to 28.5–30.0 mg O2/(gVSS h)) and the inhibition to Vibrio fischeri was eliminated. An effluent that complies with discharge standards was obtained in all cases; however, Approach 3 revealed to be a promising solution for treating this effluent as it leads to smaller operating costs. Therefore, the use of dissolved iron resulting from Fentons oxidation as coagulant in the second stage was shown to be an innovative, efficient and economically attractive strategy for treating these effluents.

Application of Fenton's Reagent for Acrylic Dyeing Wastewater Decolorization, Organic Matter Reduction and Biodegradability Improvement

Abstract Fentons reagent oxidation was employed for organic matter and color removal, along with biodegradability improvement, of a synthetic acrylic dyeing wastewater, previously treated by coagulation/flocculation. The initial iron load in the Fenton’s stage varied from the residual soluble iron concentration resulting from the coagulation/ flocculation process (which was 275 mg Fe/L) up to 400 mg/L, by adding increasing amounts of ferrous sulfate. The combination of the two treatments led to overall removals of 99.8, 84.2 and 78.6% for color, dissolved organic carbon (DOC) and chemical oxygen demand (COD), respectively, complying with maximum allowable discharge values. The Fenton process was also directly applied to the effluent. Under the optimum conditions, the color removal (99.5%) was similar to that obtained in the combined process, but DOC and COD removals were lower (66.5 and 65.1%, respectively). An improvement of the wastewater biodegradability was observed in such condition: the specific oxygen uptake rate and BOD:COD ratio increased from < 0.2 to 17.9 mgO2/(gVSS.h)) and from ~0 to 0.40, respectively. The effluent toxicity also decreased, from 97 to 29% (30 min contact time), allowing the subsequent integration of a biological process.