EU Project PHOTOMEM - Photocatalytic and Membrane Technology Process for Olive Oil Mill Wastewater Treatment

Olives undergo a series of treatments and operations in order to reach the point at which oil is extracted from them. One of the last steps in olive oil production is the purification and final separation of the olive oil from the residual pulp and an aqueous suspension, called olive mill wastewater (OMWW).

The water present in the OMWW is partially added during the process, in major extent in the three phase process. This waste water stream is a strong pollutant because of its high organic load and phytototoxic, due to the presence of antibacterial phenolic substances, resistant to biological degradation.

Mediterranean countries are strongly affected by this serious environmental problem since they produce 95% of the worldwide olive-oil. In these countries about 11 million tons of olives are produced per year from which around 1.7 million tons of olive oil are extracted.
The seasonal polluting load of olive-oil production in these countries is equivalent to the one of 22 million people, and this huge amount of polluted wastewater is produced only during 2-3 months per year (average duration of the olive oil campaign), making the storage difficult and entailing the need of an immediate treatment to eliminate its environmental hazard.

The discharge of OMWWW is not allowed trough the municipal sewage system and/or natural effluents. Unfortunately, the available technologies for the wastewater treatment are too complicated to be operated in a mill factory environment and very expensive for to the olive oil business.

For this reason, the disposal systems adopted are:
- Evaporation (mainly used in Spain and Greece): the OMWW and the alpechin are stored in huge tanks or in evaporation ponds and the water is evaporated by sun throughout the year. The main problem are: the storage needs huge tanks, the evaporation leads to bad smelling air and must be performed far away from towns; also, a pollutant rich solid residue is generated and must be disposed.

- Disposal on terrains (mainly used in Italy): the legislation allows disposing OMWW on compatible and suitable terrains (which are relatively rare and need to be toughly monitored) and within certain limits (50-80 m3/ha/y). The available terrains are not sufficient when compared to the quantities produced yearly by an average olive mill factory (20-50 m3/d). The problems caused by this procedure are pollution of the groundwater layers and of the terrains.

Since these 2 methods are not always applicable, OMWW should be treated in special waste centers. A typical approach is a multiple stage membrane process coupled with a pretreatment, typically a flocculation. The purification through membranes enables the reduction of the organic content down to 99% with a recovery of 95% of the feed stream in each batch.

However, membrane processes exhibit a main drawback: severe fouling of membrane surface, which requires frequent membrane washing and dramatically reduces the membrane module lifetime, thus increasing the cost of the treatment.
This is the main reason why the regulation is commonly not followed. The delay in solving this kind of problem originates from the lack of solutions by conventional processes.

SCIENTIFIC AND TECHNOLOGICAL OBJECTIVES:
Olive oil producers (SMEs) need a reliable and affordable technology solution to treat the waste water, since the presently applied methods are not acceptable from the environmental point of view, and conventional treatment not suitable from the economic aspect.

PHOTOMEM proposes to apply a novel technical solution based on degradation of organic pollutants through photocatalysis by using titania nanoparticles with a magnetic core for their reuse.

It the last 20 years, it has been demonstrated that semiconducting materials mediating photocatalytic oxidation of organic compounds can be an alternative to conventional methods for the removal of organic pollutants in water and air.

Ferromagnetic titania nanoparticles represent the key to solve the purification of OMWW, since they can grant high level of organic pollutants degradation through photocatalysis, together with an efficient and simple recovery of the photocatalyst.
Moreover, the great COD reduction achievable in the photocatalytic stage will drastically reduce the fouling problem on membranes, making plant operation simpler and cheaper. In order to complete the OMWW treatment, a multistage membrane process can be adopted.

PHOTOMEM aims to achieve a reliable, fast and economic olive mill wastewater (OMWW) treatment, defining and implementing a process based on 3 sequent steps:
1. Flocculation of OMWW by using low amounts of aluminium sulphate,
2. Photocatalytic COD reduction process by using magnetic titanium dioxide nanoparticles and UV irradiation, reducing the COD content from 80 g/l down to 25 g/l
3. Membrane filtration: a series of membranes operating in batch mode to reduce the COD from 25 g/l down less 0,5 g/l, that is under the upper limit for the discharge in the municipal sewer.

ADVANTAGES OF THE PHOTOMEM TECHNOLOGY :

The use of the photocatalytic treatment can grant relevant advantages with respect to presently applied pretreatments. In fact:
1. It requires less than ¼ of aluminium sulphate used in the flocculation stage to remove both the suspended solid and 1/3 of COD, with an overall cost saving of 35 %.
2. It performs by the photocatalytic operation a reduction of COD up to 70% in a relatively short time (few hours).
3. It drastically lowers the investment and operating cost of membranes (about 1/4);
4. It strongly inhibits fouling problems, thus leading to an increase of 2 times of the membrane lifetime;
5. It makes process operation easier and less expensive (50 % cost saving).
6. It will allow an automatic operation of the plant;

The reduced costs will not influence the quality of the outcome and efficiency of the overall process. In fact, the new technology will allow the achievement of:
1. A recovery of more than 85% of wastewater as purified water to a grade compatible with irrigation use and/or dischargeable at low cost in the civil municipal sewer system.
2. The production of less than 10% of organic dry mass coming from the concentrated wastewater, suitable for compost production and thus as terrain fertilizer.

STATE OF THE ART TECHNOLOGIES:

At the moment the cost of the technology available in the market is so high and the relevant operation so complex that practically no mill factory is provided with a treatment plant to dispose the produced OMWW stream. Various technological proposals have been made, including:

1. Chemical - Physical Treatments
These techniques have proven to be ineffective or not convenient because of the high cost of installation and maintenance and have not been applied in the olive processing sector. Their main problems are:
• Sedimentation of the small suspended particles cannot occur in a reasonable time frame since it depends upon the breaking of the colloidal system
• Filtration with ordinary methods is not possible since the dimensions of the micelle constituting the colloidal system run between 10-6 and 10-3 mm and are therefore too small to be separated.
• Thermal concentration and incineration: these methods of course do not allow the recycling of the water and are moreover time-consuming and, in any case, have a non-positive impact on the environment
• Freezing: neither cost effective nor easily applicable in this situation

2. Chemical methods
Although chemical methods do not seem to be the most suitable for purifying waste waters coming from oil production, researches has been carried out in this area using:
• chloration columns
• absorption with different hydroxides
These techniques have not yielded results that are satisfactory enough to be taken into consideration.

3. Microbiological methods
This kind of purification consists in the destruction of the organic substances by the action of micro-organisms, whether in the presence or absence of oxygen, in a direct way or by oxidation phenomena (H2O2/UV or ozone) in:
• aerobic purification
• anaerobic purification
Effective results by means of biological purification are difficult to achieve in reasonable residence times because of the toxicity and of the presence of insoluble organic matter.

4. Membrane treatments
Membrane treatment are state of the art for several kinds of water treatments and are applied in some cases also for the treatment of OMWW. The main problem is the high level of fouling produced by the high COD charge of the streams. Hence pre-treatment processes are needed in order to inhibit fouling.
Most applied solutions are conventional processes such as coagulation, flocculation, ozonation or biodegradation. These processes have limited efficiency, give rise to additional problems and do not meet alone or taken in combination the required purification targets. The system, with needed know how, will be commercialised directly and indirectly to the olive oil production industry; patents on the ferromagnetic nanoparticles production will be sought after, and the plant will be used by the project partners for wastewater treatment or any other use they intend to make of it. The release of licenses for these results will be also evaluated.

SUCCESSFUL COMPLETION OF THE PROJECT

On 29th-30th November 2012, the Consortium will meet in occasion of the Final Project Meeting, and SMEs will receive an intensive training session on the functioning of the plant, located outside LABOR facilities. The successful completion of the project and the implementation of the pilot plant planned in the project will be assessed once the tests on real OMWW will be finalised, and the developed technology will be evaluated for commercialization by the member SMEs.