Effect of clay pretreatment on photofermentative hydrogen production from olive mill wastewater
Introduction
The olive oil industry has been playing an important role throughout the Mediterranean region, which accounts for approximately 95% of the worldwide olive oil production (Ergüder et al., 2000). The manufacturing process of olive oil usually produces an oily phase, a solid residue and a dark colored aqueous phase, the latter of which arises from the water content of the fruit (vegetable water). The so called olive mill wastewater (OMW) consist of a mixture of this vegetable water, some soft tissues from olive pulp in a relatively stable oil emulsion, and the process waters of the machinery cooling and fruit washings steps.
In Mediterranean countries, annual OMW production is estimated to be over 30 million m3 (Sabbah et al., 2004), and around 1 million m3 of this quantity is produced in Turkey (Eroğlu et al., 2004). This dark colored wastewater has a high chemical oxygen demand (COD) and a high biochemical oxygen demand (BOD5) values reaching up to 200 g/L and 100 g/L, respectively. OMW is generally composed of water (83–94%), organic matter (4–16%) and mineral salts (0.4–2.5%) (Ramos-Cormenzana et al., 1996, Paredes et al., 1999). The main organic constituents are oils (1–14%), polysaccharides (13–53%), proteins (8–16%), organic acids (3–10%), polyalcohols (3–10%) and polyphenols (2–15%) (Cabrera et al., 1996). As a consequence, the disposal of such a pollutant waste material is an important environmental problem that needs to be solved urgently.
In general, most of the treatment processes used for high-strength industrial wastewaters have also been applied to olive mill wastewater. A number of OMW treatment methods have been employed in recent years and these can be divided into physico-chemical and biological ones (Pizzolato et al., 2002, Oukili et al., 2001).
Dark color is one of the main indicators of water pollution, since it holds up the transmission of sunlight into a stream and reduces the photosynthetic activity of microorganisms (Kadirvelu et al., 2000). Color removal and the treatment of polluted water can be achieved with one or more of the following methods: adsorption, chemical degradation, photodegradation or biodegradation processes (Pizzolato et al., 2002, Oukili et al., 2001, Dias et al., 2004). Much of the research in color removal from wastewaters has been conducted by adsorption in low-cost materials such as silicates and zeolites (Yeh and Thomas, 1995, Mansi, 1996) and by advanced oxidation processes (H2O2/UV, UV/TiO2, O3/UV, Fe2+/H2O2) (Bellekhal et al., 2006, Liao et al., 1999). Although the photobiological H2 production capability of diluted OMW samples was found to give satisfactory results (highest H2 yield by 2% (v/v) OMW containing media was , enhancement of the photobiological system is needed due to the dark color and bacteriostatic effects of OMW (Eroğlu et al., 2004).
One of the powerful treatment processes for the inexpensive removal of color from water is adsorption. Adsorption techniques have proven successful in removing colored organics (Santi et al., 2008). Several adsorbents (such as activated carbon, natural clay, bentonite, silica, cement, charcoal, etc.) are eligible for such a purpose (Crini, 2006). Clay treatment is widely used in industry for separation, purification, and recovery processes. Adsorption with natural clays has great importance due to the ease of operation, comparable low-cost of application, and relatively high specific surface area.
Oukili et al. (2001) proposed the use of the clay as adsorbent and hydrogen peroxide as oxidant for the physico-chemical treatment of OMW, in order to clarify water from the black-brownish color and to reduce the amounts of both polyphenols and the COD. Within this study, the bleaching led to 87% decrease of polyphenols and 66% decrease of COD, whereas the structure of clay had an effective catalytic and adsorbent effect on the removal of polyphenols. The color was observed to be changed from black-brown to translucent yellow. This remaining yellow-colored liquid can be retreated by other processes such as biological ones in order to remove the phenolic compounds that are responsible for the yellow color.
After post-treatment using clay, Al-Malah et al. (2000) observed the decolorization of OMW with 81% removal efficiency of phenolic compounds and 71% of organic matter. In that study, a series of treatment steps composed of settling, centrifugation and filtration was consecutively used to condition OMW. Next, the filtrate was subjected to a post-treatment process with adsorption on clay molecules. The maximum adsorption capacity for the tested concentrations of clay was reached in less than 4 h. It appears that the adsorption of phenols and organics was reversible and mainly caused by the hydrophobic interactions.
The main objective of the current study is to develop a suitable two-stage process including clay pretreatment process followed by photofermentation; this will yield an efficient hydrogen production in addition to the significant remediation of OMW.
Clay pretreatment technique was chosen due to its confirmed remediation potentials (Eroğlu et al., 2006). Photofermentation experiments were to be carried out in small-scale bioreactors (55 mL) under indoor conditions, which gave the opportunity to investigate comparative experiments by operating several parallel runs.
Attempts in this two-stage process also include extensive analyses to investigate the effect of pretreatment on photofermentation. Such a study is unique in this research area due to the simultaneous comparison of many parameters. These analyses are total phenol, total sugar, color, specific organic acids, phenols, amino acids, sugars, alcohols, gases evolved, cell concentration and pH. The precision of these results was also checked by applying mass balance equations on each stage of the process. The overall results obtained throughout this study may open a new opportunity for the olive oil industry and biohydrogen research as a result of the effective utilization of OMW at the end of these combined processes.
Section snippets
Olive mill wastewater
Olive mill wastewater samples were collected from a centrifugal olive oil mill in Izmir district (Western Anatolia).
Pretreatment with clay
Cloisite® Na+ was used as natural, white colored and fine-grained clay material. Characteristics of clay molecules were given by Eroğlu (2006). Clay pretreatment process was carried out by following the procedures given in Eroğlu et al. (2006).
Photofermentative hydrogen production
Effluent of clay pretreatment process was exposed to further manipulations such as dilution, pH change (6.8), and sterilization before
Properties of olive mill wastewater
The olive mill wastewater samples utilized throughout this study were obtained from a traditional olive oil mill in Izmir–Bornova (Western Anatolia). Since the physico-chemical properties of OMW depend on local and seasonal factors (i.e., type of processed olive fruit; oil extraction technique; harvesting time; cultivation area and etc.), a detailed analysis of each sample is extremely essential for such studies. The main characteristic properties of the OMW samples are given in Table 1.
As can
Conclusions
Compared to the photofermentation with raw OMW , the amount of hydrogen production was improved by 100% during photofermentation with the effluent of clay pretreatment process . The main reasons for the improvement of hydrogen production by clay treatment can be attributed to the high removal of the hardly biodegradable compounds such as phenols (∼80%); minor removal of organic acids, sugars and amino acids (∼20%) that are known to enhance photofermentative hydrogen
Acknowledgements
This study was supported by the Turkish State Planning Agency and METU Research Fund (BAP-08-11-DPT.2005K120600 and BAP 2003-07-02-02). We also would like to express our sincere gratitude’s to Dr. Tamay Şeker for HPLC analysis carried out in the METU – Biotechnology Central Research Laboratory.
References (35)
- et al.
Olive mills effluent (OME) wastewater post-treatment using activated clay
Sep. Purif. Technol.
(2000) - et al.
Olive oil mill wastewater treatment by the electro-fenton process
Environ. Chem.
(2006) - et al.
Land treatment of olive oil mill wastewater
Int. Biodeterior. Biodegr.
(1996) Non conventional low-cost adsorbents for dye removal: a review
Bioresour. Technol.
(2006)- et al.
Activity and elution profile of laccase during biological decolorization and dephenolization of olive mill wastewater
Bioresour. Technol.
(2004) - et al.
Anaerobic treatment of olive mill wastes in batch reactors
Process Biochem.
(2000) - et al.
Substrate consumption rates for hydrogen production by Rhodobacter sphaeroides in a column photobioreactor
J. Biotechnol.
(1999) - et al.
Photobiological hydrogen production by using olive mill wastewater as a sole substrate source
Int. J. Hydrogen Energy
(2004) - et al.
Biological hydrogen production from olive mill wastewater with two stage processes
Int. J. Hydrogen Energy
(2006) - Eroğlu, E., 2006. Biological hydrogen production from olive mill wastewater and its application to bioremediation....
Optimisation of Aspergillus niger growth on olive mill wastewaters
Appl. Microbiol. Biotechnol.
Activated carbon from an agricultural by-product, for the treatment of dyeing industry wastewater
Bioresour. Technol.
Aspects of the metabolism of hydrogen production by Rhodobacter sphaeroides
Int. J. Hydrogen Energy
Kinetics of biological hydrogen production by Rhodobacter sphaeroides O.U.001
Int. J. Hydrogen Energy
Simultaneous removal of COD and color from due manufacturing process wastewater using Photo-Fenton oxidation process
J. Environ. Sci. Health A
Decolorizing wastewater in a fixed bed using natural adsorbents
Sep. Sci. Technol.
Efficiency of light energy conversion to hydrogen by photosynthetic bacteria Rhodobacter sphaeroides
Int. J. Hydrogen Energy
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