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Olive oil inspires novel nanotechnology wastewater cleanup material

(Nanowerk Spotlight) Olive oil is good for your health. Unfortunately, the production of olive oil is not. During the olive oil production process, olive oil mills produce a liquid waste called olive black water or olive-oil-mill wastewater (OMW). This waste water has significant polluting properties due to its high levels of chemical oxygen demand (COD), biochemical oxygen demand (BOD), and phenols. In Mediterranean countries, which account for approximately 95% of the worldwide olive oil production, the annual amount of OMW is estimated to be over 30 million cubic meters. Disposal of OMV has therefore always been an important issue in this region especially since conventional wastewater treatment methods are relatively ineffective for removing the kind of pollutants found in OMW.
On the other hand, OMW may also be regarded as an inexpensive biomass source of inorganic and organic compounds. Using suitable separation processes, these compounds can be recovered and transformed into products for use in agriculture, environmental biotechnology processes, and industry.
A study conducted in 2002 by scientists in Italy ("Recovery and Characterization of the Metal Polymeric Organic Fraction (Polymerin) from Olive Oil Mill Wastewaters") found that the metal cations that are naturally occurring in OMW were mainly bound to the organic polymeric fraction with K+ being the most abundant metal. In addition, this fraction showed much lower COD and BOD values in comparison with those of raw OMW.
The researchers of this 2002 study recovered this biomaterial, which they named polymerin, with the aim of studying its recycling in agriculture and environmental biotechnology processes.
"The characteristics of polyelecrolyte of polymerin and its relatively high content of the very removable K+ suggest this biomaterial may be used as a potential biofilter for solutions contaminated by heavy and/or unwanted metals" says Dr. Renato Capasso, first author of the above study. "In fact, the potential use of plant biomass for decontamination of wastewaters by biosorption of pollutants is of great importance and interest because it allows the resolution of both the problem of their disposal and the decontamination of wastewaters by environmentally clean processes."
New research by Capasso's team at the University of Naples and Dr. Baoshan Xing's group at the University of Massachusetts has now investigated the interaction of complexing dissolved organic matter with aluminum oxide nanoparticles.
"The comparison between the behavior of minerals in nano- and microparticle form interacting with an organic matter is a new topic" Xing explains to Nanowerk. "Moreover, it is the first time that a polymerin-nanoparticles complex has been tested for potential environmental technology applications."
The researchers demonstrated that it is possible to use polymerin to adsorb phenanthrene – one of the most hazardous compounds in the ecosystem, derived mostly from the combustion of carbon fuels such as coal, oil, gas, wood, etc – from polluted waters and that by mixing aluminum oxide nanoparticles with polymerin and drying the complex they can notably increase the effectiveness of this process.
"Our results showed that aluminum oxide nanoparticles adsorbed an amount of polymerin nearly 100 times higher than microparticles" says Xing. "In addition, we found that a dry complex using nanoparticles and polymerin adsorbed twice the amount of phenanthrene than polymerin alone and 70 times the amount compared to a polymerin-microparticles complex."
Polymerin is a negatively charged water-soluble matrix and therefore it is difficult to separate it from the solution once the binding process is done. Xing and Capasso had the idea to immobilize polymerin on an insoluble support. Since aluminum oxides are positively charged at neutral and acidic pH, they seemed suitable for this purpose.
By coating the oxides with a negatively charged organic matter, it is possible to change their hydrophilic surface into relatively hydrophobic after drying the complex, which have a great affinity for soil and water polluting compounds such as hydrophobic organic chemicals.
Xing mentions that several studies suggest the application of aluminum oxides coated with anionic surfactants in wastewater treatment techniques. "Polymerin could represent an advantageous alternative to the use of surfactants: The use of polymerin instead of synthetic surfactants may be convenient because it derives from a cost free material and its recovery is very simple and not expensive" he says. "Moreover, since polymerin by itself is soluble in water, it cannot be readily used in biobeds, which need solid materials. Thus, by coating aluminum oxides with polymerin we may obtain a new solid sorbent for a biobed system."
One of the areas where this novel material could be used is the cleaning of wastewater from agricultural plants.
"A number of reactors in series, equipped with an agitator system, may contain the sorbent" Xing explains a possible setup. "After the sorption saturation, the aluminum oxides/polymerin system may be recycled by incinerating the organic fraction, this being a low cost material. The mineral fraction may be recovered and reused for further applications."
These research findings, first-authored by Marianna Iorio, have been reported in the May 27, 2008 online edition of Environmental Pollution ("Sorption of phenanthrene by dissolved organic matter and its complex with aluminum oxide nanoparticles").
By Michael is author of two books by the Royal Society of Chemistry: Nano-Society: Pushing the Boundaries of Technology and Nanotechnology: The Future is Tiny. Copyright © Nanowerk

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