This project is funded by Cyprus Research Promotion Foundation

“Sustainable management of agro-industrial wastes:

Valorization and solar-Fenton post-treatment of olive mill effluents

(OME)”

AEIFORIA/FISI/0609(ΒΕ)/12

Deliverable 15. Manual of the project objectives, methodology and results

The results are confidential data

Olive oil production takes place in Cyprus as well as other Mediterranean countries such as

Spain, Italy, Portugal and Greece from ancient times. The yearly olive oil production around

the world is estimated to be around 1.5 to 1.7 million tons per year. Mediterranean countries

produce around 98% of this olive oil, from ca. 714 million growing olive trees. Europe

accounts for 75% of the world production, with Spain being the largest oil producer (36%).

Olive oil processing has been an important and traditional industry for our country

throughout history with the 1st olive press from the Cypro-classical to the Hellenistic I period

(5th - 2nd century BC), in the city of Nicosia. The good weather in Cyprus helps the olive

maturity and processing, and hence the production of olive oil. Particularly, it is produced

seasonally between November and March by a large number of small olive mills scattered

throughout the country. The total amount of olive oil production in Cyprus is approximately

7 500 tones.

Pucture 1. Olive oil production accompanied by effluent generation, [1].

Olive cultivation represents an important social, economical and cultural activity. However,

the olive oil procedure generates also large volumes of liquid waste referred to as Olive Mill

Effluent (OME). A variety of methods are used in the production of olive oil, such as the

!

Introduction

two-phase and three-phase decantation. Therefore, the quantity and the quality of these

effluents depend on the technique that is used. For instance, the three-phase decanter

produces more effluent than the two-phase decanter. OME is generally characterized by dark

color, high organic load, acidic pH and by the presence of phytotoxic substances, which

make the direct discharge into freshwater or onto land impossible.

The OMEs have to be treated prior to their use due to the fact that they pose a serious

environmental threat. If waste products from olive oil processing are not safely disposed of,

they are likely to provoke soil and water pollution that may be harmful to human health, as

well as kill plant and animal life. The usual disposal of such wastewater is in evaporation

ponds and directly on soil for irrigation, [2].

Picture 2. Disposal of the OME in evaropation ponds and direct application on soil, [3].

The main objective of the SOLIVAL project was to determine the environmental risks

related to the disposal of Olive Mill Effluent (OME) and to develop new technical

approaches for economically and environmentally effective treatment of OME.

Evaporation pond Disposal in soil

Goal of the project

General objectives of the project

v To investigate the olive oil industry in Cyprus and Greece.

v To examine the operations in the olive mills and the environmental impacts related to

the olive oil production.

v To characterize the different kinds of the liquid waste samples from Olive oil

industries.

v To develop an integrated technique for the management of industrial effluents in

order to comply with the principles of sustainable development.

v To establish a new “Best Practice” for the management of olive mill effluents, a

serious environmental problem in the Mediterranean Sea basin.

v To prevent the deterioration of water quality, thus facilitating the implementation of

Water Framework Directive and the protection of inland waters and seawater,

including flora, fauna and potentially human beings from the uncontrolled disposal of

agro-industrial effluents.

The SOLIVAL project: “Sustainable management of agro-industrial wastes:

Valorization and solar-Fenton post-treatment of olive mill effluents (OME)”, aimed

at promoting the principles of sustainable development in two ways, i.e. through the

separation and recovery of high value natural compounds (HVNC) like antioxidants

from OME, and the post-treatment of the residual effluent by Fenton oxidation

induced by solar irradiation, i.e. using renewable energy source.

v To bridge the gap between laboratory scale research and technological application

through the implementation of an advanced oxidation treatment in an already existing

pilot unit.

v To promote the cooperation of the involved research institutions that have significant

experience in the specific field, thus safeguarding high level work, both in terms of

research and technology.

v To communicate and disseminated the project objectives, methodology, findings and

new insights obtained. The project results were expected to contribute to the

implementation, update and development of environmentally friendly practices and

policies and to the incorporation of environmental research to decisions related to

sustainable development in Cyprus and Greece.

Specific scientific and technological objectives of the project

v The pre-conditioning of the OME by applying a physicochemical method such as the

coagulation-flocculation process to remove the high solids content. Thus, several

materials were tested to optimize the separation of solids that could eventually be

used as soil amendment.

v The separation and recovery of antioxidant compounds (e.g. tyrosol, hydroxytyrosol,

oleuropein and polyphenols) from the OME, using solvent extraction. There is a wide

range of chemical properties in the molecules to be extracted and often a very

specific choice of solvent is required to maintain the ratio of different species in the

extract. To select the appropriate type and composition of solvent, as well as the

extraction conditions to maximize the yield and productivity of the target HVNC

from the feed material. Further, systematic studies with model solutions of individual

compounds (tyrosol, hydroxytyrosol, oleuropein and two polyphenols called caffeic

and gallic acids), with synthetic mixtures and finally with the actual OME.

v Post-valorization treatment of OME by solar-Fenton oxidation process, which is an

advanced oxidation process since OME still, contained a high concentration (g/L) of

organic matter that may not be easily biodegradable. Oxidation by hydrogen peroxide

and ferric/ferrous ions induced by solar irradiation can offer a viable means for an

effective mineralization of the effluent. To optimize the treatment conditions (i.e.

H2O2:feed COD ration, Fe:H2O2 ratio, treatment time, type of iron) and to

demonstrate the solar-Fenton process on a pilot plant.

Pre-conditioning of OME by using the Coagulation-flocculation process

Initially, for the pre-treatment of OME and more specifically for the removal of the solid

particles contained in the OME a physicochemical process was applied, called coagulation-

flocculation. This process helps the settleability of the suspended solids and hence the removal

of the high solid concentration from OME the mixture. The solid particles namely colloid

particles tend to remain dispersed and in suspension due to their negative charge. This result in

the development of repulsion forces among them and thus into a difficulty for settling down.

During the coagulation treatment, chemicals called coagulants assist insoluble particles and/or

dissolved organic matter to interact and gather together, firstly into small groups, then larger

aggregates, and finally visible “floc” particles, which can be easily removed from the treated

wastewater. Particularly, the coagulation method takes place using mostly inorganic salts such

as ferric chloride, ferrous and ferric sulfate, aluminium sulfate (i.e. alum) and calcium oxide.

Coagulation process is then followed by flocculation. Flocculation is a chemical procedure

where a flocculant additive is added into the mixture, inducing the bonding of the micro-floc

particles together to form larger, denser flakes helping therefore their separation. Flocculating

agents are classified into two categories; the inorganic and the polymeric materials. Polymeric

materials such as the anionic, non-anionic and cationic polyelectrolytes are mainly used as a

flocculant. Anionic or cationic polyelectrolytes with high molecular weight and thus longer

chain, usually work better in bridging the aggregate solids together. Moreover, they have the

Methodology

ability to be adsorbed and to form particle-polymer-particle bridges leading to bigger “flocs”,

[2, 6].

Schematic 1. Coagulation and flocculation process applied for the OME pre-treatment. The

photos show the OME samples prior to and after pre-treatment with the iron salts

(coagulant) and polyelectrolyte (flocculant).

Separation and recovery of High Value Natural Compounds (HVNC) from OME by

the solvent extraction

The recovery of polyphenols from OME provides the concurrent opportunity to obtain high-

value natural compounds and decrease the toxicity of the effluent. Preliminary experiments

were conducted in order to examine the effect of solvent on the rate of mass transport for

each one of the selected compounds in model/synthetic solutions. Solvent extraction was

tested with either model/synthetic solutions of tyrosol, hydroxytyrosol, oleuropein, gallic and

caffeic acids or actual OME. Batch equilibrium experiments were performed with four

organic solvent systems, namely ethyl acetate, dichloromethane, diethylether and a 7:3

mixture of chloroform:isopropanol under different extraction periods between 0.25 and 24 h

and a solvent to sample ratio of 100:50 (in mL). The initial concentration was 250 mg/L for

gallic acid, caffeic acid and oleuropein, and 1000 mg/L for tyrosol, according to the

scientific literature.

Post-valorization treatment of OME by solar photo-Fenton

Within the framework of the SOLIVAL project, photo-Fenton oxidation process was used as

post-treatment of the OME. Photo-Fenton is a homogeneous photocatalytic process and

belongs to the broad category of the Advanced Oxidation Processes (AOPs), which involve

the generation of highly energetic radicals such as hydroxyl radicals (HO) that are highly

oxidative species and capable to decompose organic non-biodegradable pollutants. Photo-

Fenton is the oxidative process based on the Fenton’s reaction, where hydrogen peroxide

(H2O2) and the ferrous iron (Fe2+) are used as oxidizing agent and catalyst, respectively, in

the presence of solar irradiation. Furthermore, UVA/Visible light (artificial or natural)

increases the efficiency of the process by photoreducing Fe3+ to Fe2+, producing additional

hydroxyl radicals and leading to the regeneration of the catalyst. The mechanism of hydroxyl

radical production by photo-Fenton, is shown in Schematic 2.

Schematic 2. Representation of the fundamental photo-Fenton reaction.

Fe2

+ + H2O

Fe

3

++ HO-+ HO

Fe3

++ H2O

Fe2

++ H

++ HO

hv

HO

+ RH

H2O

+ R

The efficiency of this process depends on several operating parameters, such as the

concentration of H2O2, Fe2+ and pH. These experiments are described elsewhere

Papaphilippou et al (2012), [5]. Specifically, the optimum experimental conditions for the

removal of the organic load were determined by altering one parameter while, the other

parameters were kept constant.

Furthermore, the application of solar photo-Fenton oxidation process on OME samples that

have been previously treated by coagulation-flocculation, and where phenolics extraction has

been applied was also investigated.

Application of solar-Fenton oxidation process on OME at pilot scale

The experiments were carried out in a compound parabolic collector (CPC) pilot plant

installed at the sewage treatment plant at the University of Cyprus (UCY). The pictures of

the plant are illustrated in Picture 3 whereas its specific characteristics are presented in Table

1.

Picture 3. Solar prototype photocatalytic reactor

Tank  of  OME  

Table 1. Main technical characteristics of the pilot plant used in this work.

Equipment Material and Capacity

Storage tank (OMW) 100 L Polyethylene container

Air blower (increase the dissolved oxygen) Model SLL-30 Flow rate: 26 L/min

Feed pump (effluent transfer) FMC 03/6 CAW 3 Centrifugal: 0.37 kW Capacity: 40-150 L/h

Acid dosing pump and solution tank

(pH adjustment)

Electronic pump (0.74 L/h)

20 L Polyethylene container

Peroxide dosing pump and solution tank

(Fenton process)

Electronic pump (0.74 L/h)

20 L Polyethylene container

FeSO4 dosing pump and solution tank

(Fenton process)

Electronic pump (0.74 L/h)

20 L Polyethylene container

Complete system for measurement and control of pH

Electronic measurement and control system for pH adjustment

Complete system for measurement and control of hydrogen peroxide

Electronic measurement and control system for peroxide adjustment

Compound Parabolic Collectors 6 Borosilicate glass tubes (55mm x 1.5m). Wall thickness 1.8 mm

Piping UPVC PN10

In addition, for experimental purposes a tank was placed near to the pilot reactor serving the

needs of coagulation-flocculation prior to the solar-Fenton process. The tank in which

coagulation-flocculation took place has a cone shape (Picture 4). The microflocs generated

by the coagulation-flocculation processes were settled at the bottom of the tank while the

waste that remained at the top was transported to the reactor tank.

Picture 4. A cone shape tank served for the coagulation-flocculation purposes in pilot scale.

Analytical methods

OME was supplied by a continuous three-phase olive processing plant located in Nicosia,

Cyprus and Chania, Greece. OME samples, namely EF1, EF2, EF3 and EF4 employed in

the current study, were collected during the 2011-2012 production campaign.

The involved research groups from the University of Cyprus and the Technical University of

Crete studied the quality of the OMEs by determining some of the most important

parameters, such as the Chemical Oxygen Demand (COD), Biological Oxygen Demand

(BOD5), Dissolved Organic Carbon (DOC), Total Solids (TS), Total Suspended Solids

(TSS), Total phenolics, Total nitrogen, Total phosphorus, Iron concentration and pH. All the

above parameters were determined according to the Standard Methods, [6].

Ecotoxicity assesement

Toxicity measurements of the OME samples prior and after photocatalytic treatment were

carried out to give a more complete evaluation of the efficiency of the solar photo-Fenton

process that has been used, by utilizing three types of toxicity assays: (i) Phytotestkit

microbiotest toxicity test, (ii) Daphnoxkit FTM toxicity test and (iii) Vibrio fischeri toxicity

test.

The phytotestkit measures the decrease (or the absence) of the germination and early growth

of plants, which are exposed directly to the samples spiked onto a thick paper. A control test

was performed using tap water. The plants used for the test were: Sorghum saccharatum,

Lepidium sativum and Sinapis alba.

Picture 5. Growth of L. sativum seeds in the presence of solar photo-Fenton OME treated

sample.

This test is based on the observation of the freshwater species D. magna immobilization after

24h and 48h of exposure in the samples. The experimental procedure for conducting this

assay was based on the ISO 6341:1996 standard protocol, [7].

V. fischeri bacteria (NRRL B-11177) were tested to obtain percentile bioluminescence

inhibition during 5 and 15 min exposure times. The Microtox® assay was performed

in accordance with the operational procedures from Azur Environmental Ltd.

Lyophilized bacteria (approx. one million in one preparation), using the Microtox®

kit, were reconstituted by adding a reconstitution solution, and then the suspensions

were sequentially diluted and tested at 15 °C in parallel to a negative control test. V.

fischeri toxicity test was performed on raw OME and oxidized sample

Phytotoxicity tests

Daphnia magna tests

V. Fischeri tests

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