Integrated aerobic biological treatment and chemical oxidation with Fenton’s reagent for the processing of green table olive wastewater
Introduction
Table olive processing wastewater (TOPW) causes an important local environmental problem, as it is characterised by seasonal peaks, very high organic load and high concentrations of phenolic compounds, which are known to cause toxic effects to living organisms. In Mediterranean countries, this type of wastewater is usually discharged untreated to small streams or directly to the sea. In the best cases, it is transported to evaporation ponds, where malodours are a common nuisance, while the risk of polluting surface or ground waters is not always avoided [1], [2], [3]. For green olive preparation, the characteristics of the wastewater which arises from the several treatment stages (cleaning, debittering using NaOH, washing after debittering, fermentation brines and general use water) fluctuate as follows—pH: 3.6–13.2; suspended solids: 0.03–0.4; dissolved solids: 0.2–80; BOD5: 0.1–6.6; COD: 0.3–16.2; chloride: 0.0–48.5 and sodium chloride 0.0–80.0 g/l [1]. The stages of debittering and subsequent washing constitute the largest and most heavily polluted fraction of the wastewater, seasonally produced from September to November.
In the last few years, as environmental regulations and enforcement have become more stringent, a growing interest in the development of new treatment methods for this type of wastewater has emerged. Biological treatment methods have been recognized as overall economical and effective processes [3], [4], [5], [6]. However, the presence at high concentration of aromatic, phenolic and polyphenolic compounds, which are toxic to many microorganisms (especially those found in municipal wastewater treatment plants), inhibits the efficiency of biodegradation processes [3], [7].
In order to facilitate the degradation of toxic or non-biodegradable organic substances, many researchers have proposed combined methods comprising of chemical and biological treatment steps. A common approach refers to the oxidation of the wastewater using a strong oxidative agent, such as ozone [8], Fenton’s reagent, a mixture of hydrogen peroxide and ferrous or ferric iron [9], [10], a combination of UV radiation and hydrogen peroxide as well as photo-Fenton [7]. These methods are based on the creation of very reactive oxidizing free radicals, especially hydroxyl radicals.
In Fenton’s reaction, the ferrous and/or ferric cation decomposes catalytically hydrogen peroxide to generate powerful oxidizing agents, capable of degrading a number of organic and inorganic substances. Fenton’s oxidation is a complicated system that involves a large number of reactions, including redox reactions, complexation, precipitation equilibrium, etc. Also, there is an uncertainty in the nature of oxidizing species generated during the process (formation of radical species or generation of aquo- or organocomplexes of high valence iron). A model of Fenton’s reagent processing of brines from the table olive industry, a wastewater relatively similar to that resulting from the olive debittering stage, which was studied in this work, is described by Rivas et al. [10].
In this study, wastewater from the debittering process of green table olives and the subsequent washings were treated aerobically using Aspergillus niger [11]. The Aspergillus genus has been used successfully for the bioremediation of olive oil mill wastewater, which is also characterized by high organic and phenolics content and satisfactory removal efficiencies have already been reported [12], [13], [14]. Fenton’s reagent was used as a secondary chemical treatment step for the oxidation of the recalcitrant organic compounds or metabolites of those that could not be oxidized biologically. The use of chemical oxidation as a secondary treatment process offers the advantage of reducing the amount of the required oxidants and improves the economic feasibility of the treatment process.
Section snippets
Wastewater
Fresh washing and debittering wastewater (TOPW, pH 12.1–12.5, conductivity 24–44.3 mS/cm) was obtained from the industrial plant of the Agroindustrial Cooperation of Stylida (Lamia, Central Greece). Before biological treatment, the pH was adjusted to 4.5–4.8 using an average of 5.06 ml/l conc. H2SO4. COD and conductivity of TOPW after pH correction ranged from 6.50 to 13.55 g/l and 12.5 to 22.2 mS/cm, respectively.
Inoculum
A strain of A. niger isolated from undiluted TOPW was used for the biological
Aerobic biological treatment of green table olive wastewater
Fig. 1 shows the COD, pH and VSS evolution during the initial 3 day batch culture and the subsequent continuous culture, during which the hydraulic retention time of the wastewater was 2 days. After 1 day of batch operation, the COD removal was 56% and reached 71 and 74% on the second and the third day, respectively. During the continuous operation phase, the average organic loading rate was 5.4 g [COD]/l per day with a standard deviation of 1.1 g/l per day and the mean COD removal was
Conclusion
The aerobic biological treatment of TOPW with A. niger constitutes an effective method for the reduction of the organic and phenolic load of this type of wastewater. In this study, the biological treatment stage yielded a 70% COD reduction, 41% total phenolic reduction and 85% simple phenolic reduction, with a hydraulic retention time of 2 days. Biological treatment of industrial wastewaters of special composition, such as TOPW, requires a prolonged acclimatization period for the biomass, even
Acknowledgements
This work was supported by a grant from the Greek General Secretariat of Research and Technology (EPET II, 98 VIA-08).
References (27)
Wastewater from the preparation of table olives
Water Res.
(1992)- et al.
Aerobic biological treatment of black olive washing wastewaters: effect of an ozonation stage
Process Biochem.
(2000) - et al.
Combined and separate aerobic and anaerobic biotreatment of green olive debittering wastewater
J. Agric. Eng. Res.
(2001) - et al.
Kinetics of black-olive wastewater treatment by the activated-sludge system
Process Biochem.
(1994) - et al.
Treatment of brines by combined Fenton’s reagent-aerobic biodegradation. II. Process modeling
J. Hazard. Mater.
(2003) - et al.
Optimization of Fenton’s reagent usage as a pre-treatment for fermentation brines
J. Hazard. Mater.
(2003) - et al.
Removal of phenol compounds from olive mill wastewater using Phanerochaete chrysosporium, Aspergillus niger, Aspergillus terreus and Geotrichum candidum
Process Biochem.
(2000) - et al.
Olive mill wastewater treatment by immobilized cells of Aspergillus niger and its enrichment with soluble phosphate
Process Biochem.
(1997) Investigation of the Folin–Ciocalteau phenol reagent for the determination of polyphenolic substances in natural waters
Water Res.
(1983)- et al.
Treatment of hypersaline wastewater in the sequencing batch reactor
Water Res.
(1995)
Decolorization of fresh and stored-black olive mill wastewaters by Geotrichum candidum
Process Biochem.
Characteristics of p-chlorophenol oxidation by Fenton’s reagent
Water Res.
Oxidation of p-hydroxybenzoic acid by Fenton’s reagent
Water Res.
Cited by (67)
Photo-Fenton like process as polishing step of biologically co-treated olive mill wastewater for phenols removal
2023, Separation and Purification TechnologyMembrane filtration, activated sludge and solar photocatalytic technologies for the effective treatment of table olive processing wastewater
2021, Journal of Environmental Chemical EngineeringA bibliometric analysis of industrial wastewater treatments from 1998 to 2019
2021, Environmental PollutionCitation Excerpt :The composition of industrial wastewater became more complicated by containing more non-degradable organic matter with the development of the industry. Biological treatment method had the advantages of high efficiency, low cost, and convenient operation, and have played a crucial role in industrial wastewater treatment (Kotsou et al., 2004). With the researchers’ much attention and the huge amount of studies, the maturity of biological treatment technologies has improved rapidly.
Recent advances in advanced oxidation processes for removal of contaminants from water: A comprehensive review
2021, Process Safety and Environmental ProtectionApplication of biological and advanced oxidation processes (AOPs) for the remediation of wastewater laden with toxic pollutants
2020, Removal of Toxic Pollutants through Microbiological and Tertiary Treatment: New PerspectivesA combined treatment approach for dye and sulfate rich textile nanofiltration membrane concentrate
2019, Journal of Water Process EngineeringCitation Excerpt :Ozonation of real NF membrane concentrate was studied by Lopez et al. [19] and obtained an increase in BOD5 from 0 to 75 mg/L. Coupled Fenton and biological processes have increased attention for the treatment of refractory wastewater [20–22]. Fenton process is usually used as a pretreatment to improve biodegradability which indicate BOD5/COD.