Optimisation of Fenton’s reagent usage as a pre-treatment for fermentation brines

doi:10.1016/S0304-3894(02)00217-0

Journal of Hazardous Materials

Volume 96, Issues 2–3, 31 January 2003, Pages 277-290

https://doi.org/10.1016/S0304-3894(02)00217-0 Get rights and content

Abstract

Pre-treatment of fermentation brines from green olives has been carried out by the Fe(II)/Fe(III)/H₂O₂ system. Reagent concentration exerted a positive influence on chemical oxygen demand (COD) removal. Hydrogen peroxide uptake showed values in the range 0.3–1.6 mol of COD eliminated per mol of H₂O₂ consumed depending on operating conditions. The optimum working pH was found to be in the interval 2.0–3.5. Reaction temperature increased the COD degradation rate, although similar COD conversion values were obtained after 5 h of treatment regardless of the value of this parameter. An analysis of the biodegradability of this type of effluent demonstrated the beneficial effect of the chemical pre-oxidation. According to the experimental results, it is suggested that there is an inhibitory effect of the wastewater due to its COD content and nature rather than attributable to the presence of high amounts of sodium chloride. Biodegradation efficiency increased as temperature was raised up to 30 °C. A further increase of this parameter up to 40 °C resulted in the death of the microorganisms.

Introduction

A considerable number of effluents are characterised by a high content of inorganic salts, especially sodium chloride and in some cases sodium hydroxide [1], [2]. Some examples can be found in the manufacturing of pesticides, herbicides, pharmaceutical products, dyes, etc. Other processes that generate an important amount of brines are related to gas oil recovery operations, landfill leachates, meat-packing wastewater, etc. [3]. Disposal and management of this type of effluent is not an easy task. Traditionally, biological processes have been considered to be the most economical and simple option to treat these aqueous wastes [4], [5], [6], [7], [8], [9], [10]. However, this technique is not always feasible due to the toxic nature of high concentrations of, on the one hand, sodium and/or chloride and, on the other hand, the presence of a significant organic contaminant load. Woolard and Irvine [2] have recently reviewed studies carried out on the biological treatment of brines. In general, it has been demonstrated that this method does not constitute a suitable choice even when using acclimated seeds. Therefore, chemical oxidation processes seem to be appropriate to reduce the contaminant load of this kind of effluent and hence render them more biodegradable. In this sense, Lin et al. [3], based on the high conductivity of brines, have proposed an electrochemical method of treatment. Also, Rearick et al. [11] have used the Fenton system in conjunction with a series of membranes to re-use wastewater generated in the manufacturing of dyestuff.

In this study, the chemical oxidation of wastewater from the fermentation brines of table olives has been investigated. Fermentation brines are characterised by a low pH (3.5–4.5) and a high content of NaCl (6–10%). Few works have dealt with this type of wastewater. Some authors have tested a physico-chemical method based on a previous neutralisation followed by an adsorption step on activated carbon or an ionic resin [12]. Other processes, however, have been addressed to disposal of the waste into impermeable layers with no aquifers [13] or into low deep aerated lagoons. Also, the direct dumping of the saline effluents into the sea has been proposed [14].

In the present work, Fenton’s reagent has been studied for the treatment of fermentation brines. It has been demonstrated that this treatment allows for large reductions of the organic load of wastewaters at acceptably low costs [15], [16]. In addition, effluents similar in composition have already been treated with promising results. Thus, wastewater from the manufacturing of olive oil has been processed by using Fenton’s reagent, showing considerable reductions of the chemical oxygen demand (COD) of the effluent [17].

After the chemical oxidation has taken place, aerobic biological experiments have been carried out by using non-treated and Fenton’s pre-treated effluents. A comparative study has been completed to ascertain the positive or negative effects of this integrated treatment.

Section snippets

Materials and methods

Chemical oxidation experiments were carried out in a 500 ml glass reactor under sunlight conditions, batchwise and (unless otherwise specified) in the presence of oxygen. The aqueous solution of reactants was homogenised by magnetic agitation to avoid concentration gradients. Systematically, samples were withdrawn and immediately analysed after sampling (in less than 2 min). Immediate analysis of samples allowed for the analytical procedure to be completed without interference from reducing or

Influence of hydrogen peroxide initial concentration

In this work, the influence of the initial concentration of hydrogen peroxide was assessed. For that purpose, experiments were conducted at similar operating conditions but different amounts of H₂O₂ added at the beginning of the process, in the range 0.01–1.0 M. Fig. 1 depicts the evolution of COD and H₂O₂ conversion for the aforementioned experimental series.

From Fig. 1, an increase of the COD removal rate as the H₂O₂ initial concentration is raised from 0.2 to 1.0 M is observed. Additionally,

Conclusions

From the present study, the following conclusions can be drawn:

•
Usage of Fenton’s reagent allows for a significant reduction of the COD content of fermentation brines.
•
Both Fe(II) and/or Fe(III) can act as a catalyst of the hydrogen peroxide decomposition. Use of ferric iron instead of the reduced form may contribute to the improvement of the process economy.
•
Optimum working pH was situated at acidic conditions, similar to the natural pH found for this type of effluents.
•
Fenton’s reagent

Acknowledgements

This work has been supported by the Junta de Extremadura and Fondo Social Europeo (Project IPR00A002).

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Optimisation of Fenton’s reagent usage as a pre-treatment for fermentation brines

Abstract

Introduction

Section snippets

Materials and methods

Influence of hydrogen peroxide initial concentration

Conclusions

Acknowledgements

Water Res.

Water Res.

Water Sci. Technol.

Enzyme Microb. Technol.

Grasas y Aceites

Water Res.

Water Res.

Water Environ. Res.

J. WPCF

J. WPCF

J. WPCF