Titolo della tesi: DEVELOPMENT AND OPTIMIZATION OF OLIVE MILL WASTE WATER (OMW) TREATMENT BY BIO- AND NANOTECHNOLOGIES
Safe drinking water is essential to the health and welfare of a community and water from all sources must have some form of purification before consumption. Various methods are used to make water safe and attractive to the consumer. The growing competition for water and declining freshwater resources, the utilization of marginal quality water for agriculture has posed a new challenge for environmental management. In water scarce areas there are competing demands from different sectors on the limited available water resources.
Industry is a small user of water in terms of quantity but has a significant impact on quality. Today water pollution is the biggest problem for human beings due to the deterioration of the water quality because of various human activities which makes water unfit for drinking and domestic use purposes. Many dangerous diseases are also caused because of polluted water. The diseases associated with contaminated water remain serious public health problems all over the world. Olive oil production is one of the main agricultural activities in many Mediterranean countries and it usually produces huge quantities of wastewaters, since the most important environmental problem in the Mediterranean countries is the treatment of olive mill wastewater (OMW). 2546 306 tons/year (t) of olive oil is produced every year from all over the world, this amount of olive oil is produced from approximately 750 million productive olive trees, the majority of the production is in the Mediterranean region where this region alone produces 97% of the total olive oil production, while European Union (EU) countries produce 80–84%. The biggest olive oil-producing country is Spain (890 100 t in 2002), then Italy (614 950 t/year), Greece (402 703 t/year) and Turkey (168 700 t/year), followed by Tunisia, Portugal, Morocco and Algeria. Olive mill wastewater treatment is a critical problem; this waste contains an enormous supply of water, organic and inorganic matters.
There are several methods which are generally used in the production of olive oil which results in different waste products. Olive pressing is the old/ traditional technology for olive oil production, it was replaced by decanter centrifuges to separate oil from solids. Currently two phase and three phase centrifugation techniques are used for olive oil extraction from olives. In the process of olive oil production high amount of wastewater is generated which induces environmental pollution, mainly associated to high organic chemical oxygen demand (COD) concentration, phytotoxic properties and its resistance to biodegradation due to its high polyphenol and organic content.
Nowadays, the development of a technical and economical feasible treatment process of OMW represents a challenge for process engineers, since the application of conventional stand-alone treatment process is not applicable due to the high organic load (60 g/l COD), the high phenol/polyphenols content (phytotoxicity, thus leading to difficulties by applying bioremediation techniques) and the very dark and opaque color (difficulty of irradiation, thus leading to difficulties by applying photocatalysis processes) of this wastewater. As so far, several researchers worked on the olive mill wastewater treatment, the results were not up to the mark, there were some drawbacks in the whole process or individual treatment methods. Several treatment methods have been investigated, including physicochemical technologies (dumping in evaporation ponds, dilution, evaporation, filtration, sedimentation, centrifugation, coagulation, flocculation and adsorption), oxidation/advanced oxidation processes (Ozone/H2O2, UV/H2O2, wet air oxidation, Fenton oxidation, electrochemical oxidation) and biological (aerobic or anaerobic) technologies, as well as combinations of these methods and the recovery of valuable compounds (such as hydroxytyrosol and tyrosol).
Nanoparticles are of great interest for the industry due to their numerous possible applications in several fields. Process intensification techniques aim to minimize plant size of continuous, high yield equipment capable to produce specific sized, high-quality nanoparticles, combined with an increase in energy efficiency, safety and cost reduction, in this work, reviewed some adopted Process intensification (PI) techniques for nanoparticles synthesis processes employed in the food and pharmaceutical sector. By reducing the technology transfer gap, nanotechnologies may become convenient and feasible, allowing both industries to achieve the production of higher quality products with particular characteristics without sensibly increasing additional costs. This will represent in the next future a strategic key feature of industries in the global market.
In detail, this work reports a novel approach to produce nitrogen doped magnetic core TiO2 nanoparticles (NTiO2/ FM). The treatment of wastewater streams by photocatalysis appears a feasible pre-treatment for many subsequent purification steps, such as membranes. In order to keep high efficiencies in dealing with the wastewater streams, the photocatalyst requires to be suspended in order to reach the water surface for proper irradiation and operation. A main drawback is the recovery of the suspended photocatalyst, that may be accomplished by magnetic filters (up to 99.9%) as soon as the titania nanoparticles are attached to magnetic nanocores (FM). Moreover, the photocatalyst should react to visible light and not only to UV (as pure titania), to operate with a high energy efficient process by using LED lamps instead of
UV lamps. This property acquired through nitrogen doping. Therefore, the production of N-TiO2/FM may represent a general solution to all these problems. The experimental runs performed in an aerated photoreactor for phenol degradation shows the efficiency of N-TiO2/FM for purification purposes and its easily recovery by magnets. In this work other two active photo-catalysts were synthetized and tested for the removal of methylene blue and arsenic in aqueous solutions. The two catalysts (Fe3O4/SiO2/TiO2-Al and Fe3O4-SiO2/Zr-TiO2) were characterized by nano-size, guaranteeing a large specific surface area and a noticeable number of active sites and resulted active in the visible spectra (400-800 nm). The nanoparticles were characterized by BET, FE-SEM and EDS methods. The Fe3O4/SiO2/TiO2-Al nanoparticles demonstrated to be more versatile, since showed a noticeable removal efficiency considering both pollutants As (73.5 %) and methylene blue (78 %) after 24 h. The Fe3O4-SiO2/Zr-TiO2 nanoparticles showed a higher affinity towards methylene blue removal (90.5 %) whereas the As removal efficiency was negligible (0.5 %). The two nanomaterials were tested also in a bi-component solution, loading both As and methylene blue target pollutants.
Chitosan-magnetite nano-composites were produced in laboratory and used in batch experimental tests for the removal of Hexavalent Chromium, Cr(VI), in aqueous solutions. Cr(VI) is considered one of the most toxic compounds present in the Mediterranean Area due to its carcinogenic and mutagenic characteristics, besides its notable solubility and mobility in the environment. The most effective way for the remediation of Cr(VI)-polluted groundwater is represented by the combination of chemical reduction and co-precipitation processes, generating Cr(III) species, characterized by a very low toxicity and solubility in comparison to Cr(VI) ones.
After significative study of several processes for treatment of olive mill waste water, three most suitable and effective treatment methods are proposed based on the extensive review of olive mill waste treatment. All the three methods are in good sequential order, started with optimization of coagulation, photo catalysis by using Nano catalyst, followed by membrane treatment and then process system also optimized by shifting biological oxidation to second stage of treatment to increase the AOPs or Photocatalysis activity since through the biological oxidation there is a chance of high degradation of Phenols and total organic carbon. Ozonation treatment was also employed for 2 phase OMW. In this work, both wastewater streams exiting 2-phase (OMW2) and 3-phase (OMW3) olive oil production processes were considered and for both wastewater feed streams, economic considerations were performed to check process optimization.
In particular, in this work 3 phase OMW involved a pre-treatment step by coagulation and flocculation, followed by photocatalysis under visible and/or UV light by means of home-made composite Nano catalyst, membrane operation (with special insight on membrane fouling). 2 phase OMW treatment process involved pre-treatment step by coagulation and flocculation, biological oxidation, application of Advanced oxidation processes includes H2O2, H2O2/UV, Fenton, Photo Fenton (UVA, UVC and UV-Vis), Ozonation and photocatalysis using reusable core shell magnetic Nano particles coated with Nitrogen doped TiO2.
To define an efficient pre-treatment and to overcome major obstacles of membrane treatment (fouling), economic organic coagulant has been tested. Chitosan, a natural linear bio-polyaminosaccharide, is obtained by alkaline deacetylation of chitin. The main purpose of this work was to investigate the effects of chitosan as coagulant aid to reduce phenols content, COD and TOC in 3 phase OMW, in addition to control membrane fouling, which is used in the sequential step of the treatment. A conventional jar test apparatus was employed for the flocculation tests followed by photo catalysis and membrane treatment includes Nano Filtration process by means of a pilot-scale plant. For 2 phase OMW Aluminium sulphate was used a coagulant. In both 3 phase OMW and 2 Phase OMW treatment processes pre-treatments were done after an extensive optimization of parameters. Optimization of coagulation & flocculation was done by optimizing pH change, types of coagulants, dosage of coagulant, usage of flocculant and dosage of flocculant.
In this work, the technical and economic benefit of using photocatalysis as a pre-treatment step for a subsequent olive mill wastewater (OMW) treatment process by membranes will be discussed. Membrane processes appear to be suitable to purify aqueous wastewater streams polluted by organic matter such as OMW but suffer severe fouling. In order to avoid fouling, the use of operating conditions below the boundary flux are suggested. The problem is that in many cases, boundary flux values are extremely low, making the process economically not feasible. In order to overcome this limitation, pre-treatment steps are necessary to increase boundary flux values accordingly. Photocatalysis appears to be capable to achieve these requirements: on one hand, the process is capable to reduce the organic load of the feedstock and on the other hand, particle size distributions of the suspended organic matter are changed. Both principles are known in literature to lead to boundary flux value changes.