An Overview of the Environmental Problems of the Used Waters Extracted from the Factories of the Olive Oil Production, and Their Treatment Methods

The olive oil industry plays a crucial role in the agricultural economy, particularly in Mediterranean countries. Aligning the industry with the United Nations Sustainable Development Goals (SDGs) is essential for fostering sustainable agriculture, economic growth, and environmental protection. This paper explores how the olive oil sector in Albania contributes to the SDG 6: Clean Water and Sanitation which addresses the industry’s impact on water consumption and pollution. We conduct a survey in Elbasan country, related to the olive oil industry and its impact on the environment. The environmental audit of the Olive oil mill in Selita village result in water and soil pollution because of the septic tank wastewater treatment method applied to the olive oil effluent. In Albania we face this problems in many other olive oils factories. Based on the study results we proposed the mitigation measures to protect environment. We analyzed and proposed the best scenario to treat wastewater for olive oil mills in Elbasan County.

Introduction

The United Nations introduced the SDGs in 2015 to address global challenges such as poverty, inequality, and environmental sustainability [1]. The SDGs are a call to action for all countries, rich, poor and middle income in order to promote prosperity and protect the planet. They are an acknowledgement that the implementation of strategies to promote economic growth and address social needs such as education, health, and social protection and job opportunities is the most feasible way to definitively end poverty, while emphasizing climate change mitigation and environmental protection [2]. The olive oil industry, as a major agricultural sector, has significant potential to contribute to these goals.

SDG 6: Clean Water and Sanitation – Addresses the industry’s impact on water consumption and pollution [3].

Water consumption in olive factories is part of the production process (pressing and centrifugation) of olive oil.

The amount of water used, especially in the final stage of oil production, plays an important role in the final quality of the produced oil, in the efficiency of production, but also in the nature and characteristics of the by-products (residues) at the end of the process. A large consumption of water is also observed in the initial stage, washing of olives where about 50% of the water is used. Below are listed all the stages of the olive processing where water is consumed [4].

The olive washing processes are: i) pressing, ii) crushing, iii) extracting, and iv) iltering. Water consumption is not limited only to the processing process. If we analyze more widely, then water consumption increases relatively much if we include the necessary water needed in the process of cultivation, irrigation, etc. [4]. Water is added in some of these steps to squeeze out most of the oil from the olive. The mix between olive vegetation water and this under-process added water is called olive mill wastewater (OMWW) [5].

The olive sector occupies a strategic place in the culture and economy of the Mediterranean countries, which contribute 95% to the world’s olive and olive oil production [6]. The olive and olive oil sector is one of the main agro-food sectors in Albania, where over 100,000 farmers (about a third of the farmers in Albania) are involved in olive cultivation. Since 2013, production in this sector has been continuously increasing, but in 2019, a decrease in production has been observed even though the number of cultivated plants has been higher compared to previous years, this may have come as a result of a number of factors that affect production such as: bad weather in spring, lack of rain at the key moment of olive development, the spread of diseases, poor agronomic practices etc. While 2019 was considered a bad year for production, especially for Berat area, from 2020 onwards production has been quite high, reaching the highest production in 2022 [7], [8].

Elbasan is the third most important region in terms of olive production, where the olive for oil production dominates. This area has 19,598 plots of land spread over 9,763,216 ha.

Nevertheless, this sector consumes a lot of water for oil production: approximately the water footprint of 1 L of olive oil is 3914 L, whereas around 3.51 L of water is exploited during the processing steps [9]. Moreover, it generates a massive quantity of wastewaters, about 5.4 × 106 m³ of olive wastewater vs. 1.8 × 106 tons of olive oil are annually produced worldwide [10].

In the Albanian legislation, there is no normative act or regulation for the way of management of olive oil processing waste or their reuse in different fields such as agriculture or energy.

Material and Method

Themill that processes olive oil in the village of Selite, is taken as a case study. It was built in 2023 (with the start of the olive season), approximately 33 km from the city of Elbasan and 18 km from the city of Cerrik. The surface of the building is 510 m², while the plot has an area of 2500 m². The coordinates of the olive oil mill are X = 40.890678 and Y = 19.980561 (Gauss–Kruger system) (Fig. 1). This factory has implemented the 3-phase system technology, where three products are obtained at the end of the olive processing process: olive oil, olive pomace (husk) and wastewater.

Fig. 1. Satellite image of the olive oil mill (photo withdraw form Google map).

Some of the main processes that take place in the olive oil processing plant are: weighing, washing the olive kernels, kneading, centrifugation, etc. The process of washing olives is realized by spraying water to remove associated residues such as leaves, dust, stones, mud, etc. The water used for washing olives is fed into the equipment by a pump and then removed by a discharge pipe as shown in Fig. 2.

Fig. 2. Intake of water through the pump (a) and removal of used water through the discharge pipe (b).

The last process of olive oil processing is the centrifugation process, which also depends on the type of olive oil mill. As we mention above the mill consists of a three-phase system, so the horizontal cylindrical shaft separates the oil paste into three components.

The olive oil, after passing through the final filter, is placed in the relevant packaging containers, the liquid goes outside through a rectangular pipe, while the wastewater leaves the cylindrical shaft through a pipe to be discharged into the septic tanks located outside the factory. In the installed septic tanks, only wastewater is allowed to be discharged (Fig. 3a), while the water used for washing olives can be used for irrigation of agricultural crops since they do not contain substances that limit the development of plants or the quality of the soil. Wastewater from the olive oil mill due to their phytotoxic composition, need a preliminary treatment before their use. Septic tanks consist of three rooms that communicate with each other through pipes (Figs. 3a and b). At the end of each room, there are sluice gates that can only be opened when the vegetation waters have stabilized, while grease collectors are also installed in the third room, as well as pipes for the removal of treated water that can be used in agriculture (Figs. 3c and d).

Fig. 3. Septic tank (a), (b) (rooms 2 and 3), discharge through the sluice gate to the drainage channel (c), (d).

The water consumption in olive oil mills during the year 2022 will be calculated based on the type of mill (Table I).

Table I. Water Consumptions Rates at Mills [11]

Mill type	Water consumption rates (l/ton of processed olive)
	Measurement Results (range)	Theoretical (RAC/CP)
Traditional	(320–400) l/ton	(400–600) l/ton
Two Phase	(250–350) l/ton	(120) l/ton
Three Phase	(750–980) l/ton	(700–1000) l/ton

The volume of olive oil mill wastewaters (OMWWs), analytically can be calculated based on the amount of olives that were used for the production of oil of olives in Albania and in particular in the Elbasan county during the year 2022 (see Table II).

Volume of OMWWs=Number of olive ×Volume of water consume in the mill [11]

Table II. Annual Production of Olives for Oil (INSTAT, 2022)

Agricultural production of olives in tons used for olive oil extraction
In Albania	In Elbasan County
157,700 ton	64 ton

Results and Discussions

The volume of olive oil waste water produced in Albania for the year 2022 is given below:

1. If we assume that all olive oil mills in Albania are of the traditional type: Volume of OMWW=Number of olive ×Volume of water consume in the mill  157,700ton×400lton=63,080.000l OMWWs Volume in m3=63,080.000l×10−3=63.080m3OMWWs

2. If we assume that all olive oil mills in Albania have a 2-phase system: Volume of OMWWs=Number of olive ×Volume of water consume in the mill  157,700ton×325lton=51,252.500l OMWWs Volume in m3=51,252.000l×10−3=51,252.5m3OMWWs

3. If we assume that all olive oil mills in Albania have a 3-phase system: Volume of OMWWs=Number of olive ×Volume of water consume in the mill  157,700ton×950lton=149,815.000lOMWWs Volume in m3=149,815.000l×10−3=149,815m3OMWW

The volume of olive oil waste water produced in the Elbasan County for the year 2022 is given below:

1. If we assume that all olive oil mills in Elbasan are of the traditional type: Volume of OMWWs=Number of olive ×Volume of water consume in the mill  25,564ton×400lton=10,225.600lOMWWs Volume in m3=10,225.600l×10−3=10225.6m3OMWWs

2. If we assume that all olive oil mills in Elbasan have a 2-phase system: Volume of OMWWs=Number of olive ×Volume of water consume in the mills  25,564ton×325lton=8,308.300l OMWWs Volume in m3=8,308.300l×10−3=8,308.3m3OMWWs

3. If we assume that all olive oil mills in Elbasan have a 3-phase system: Volume of OMWWs=Number of olive ×Volume of water consume in the mill  25,564ton×950lton=24,285.800lOMWWs Volume in m3=25,285.800l×10−3=24,285.8m3OMWWs

As we mention the Olive oil in Selite uses the 3-phase system to produce olive oil (Fig. 5).

The wastewater treatment plant of the olive oil mill in Selite is a very low cost plant that uses anaerobic biological treatment method (Figs. 4 and 5). The wastewater is treated to these septic tanks which are filled during the olive oil season, and then the heavier particles will settle to the bottom thanks to the force of gravity, thus creating the stratification of the mass, which is removed step by step.

Fig. 4. Cross section of septic tanks.

Fig. 5. Three-phase olive oil extraction process [13].

Wastewater remains in these septic tanks until the following period of olive production, since the anaerobic process takes a long time to occur, due to the biodegradability of phenolic compounds. Below in Fig. 6 is the view of the vegetation waters produced during the olive season. This black liquid wastewater is composed of the olive fruit vegetation water, the water used for washing and treatment and a portion of the olive pulp and residual oil [14].

Fig. 6. Schematization of vegetation water stratification and photo of wastewater during the olive season.

The OMW is a foul smelling acidic wastewater composed of water (83%–92%), organic matter (4%–16%) and minerals (1%–2%) [15]. The organic load reflected in the high BOD (up to 100 g/1) and COD (up to 200 g/1) concentrations [14] comprises sugars, nitrogenous compounds, fatty acids, polyalcohol, polyphenols, pectin and fats [16].

Three Possible Scenarios of Olive Oil Wastewater Treatment

First Scenario

The construction of central plants with advanced technologies is associated with high costs, thus significantly reducing the profit of olive oil processing factories. The operational cost for treating 1000 m³ of vegetation water, for a 90-day operating period of the oil processing plants of olive is shown in Table III [17]:

Table III. Operational Costs for Olive Oil Waste Water Treatment [17]

Treatment method	Cost for 1000 m3
Aerobic	23 000 euro
Anaerobic	18 000 euro
Chemical oxidation	27 000 euro
Adsorption	24 000 euro

Based on the table above, the cost for a factory with average processing capacity, with a production of about 2000 m³ of olive oil waste water goes to very high figures. Moreover, being that the techniques presented in the table are insufficient for wastewater treatment if are used separately, their combination is required, leading to increased costs. This makes it impossible to install treatment units in factories individually, so central plants are suggested.

The most effective treatment in the case of central plants is anaerobic digestion. Its advantages are: biogas production, low produced volume of solid waste, demand relatively low for energy etc. Although anaerobic treatment alone is not sufficient, therefore additional physic-chemical treatment is suggested. Joint treatment of processing waste olive oil, together with waste from other agro-industrial factories or urban wastewater, it is an expensive and bulky solution, since preliminary treatments are required and done dilution before sending to the central plant, as well as we have a very large increase in the volume of wastewater to be treated, which translates into the need for very large plants and higher operating costs.

Second Scenario

Olive oil wastewater treatment individually from each olive oil processing plant, requires the application of low-cost methods. As individual treatment methods are inappropriate or ineffective if used individually, it is necessary to combine several techniques. The most satisfactory method and low cost and that is widely applied are evaporation tanks in combination with the addition of CaOH₂ to reduce unpleasant odors and lower COD levels. The processing of 1000 m³ of olive oil waste water requires approximately 1000 m² (0.1 ha) of land for their treatment in evaporation tanks. This technique is suggested for mills with small capacity, because it requires large areas of land.

Third Scenario

This scenario it is proposed for small mills in vicinity of each other, so it can be possible to collect their wastewater for treatment. In these units, the treatment includes: collection of waste, sedimentation (decantation) of and the neutralization of the acidity of olive oil waste waters with lime about 2% of its volume waste, storing them in a tank (which must be isolated in the bottom and with a depth of 1.5 m) and then can be used to irrigate the olives at a rate of 20 m³/ha/year, [17]. Location selection, construction and operation of such an object is determined based on several criteria. The most important criteria is the distance from settlements and sources of drinking water, which should be about 300 m. To avoid transportation cost, it is recommended that the treatment unit be inside the territory of the factories or near them. Regarding the type of soil, a soil should be selected where underground aquifers to be deeper than 15 m, not to be sandy, watery or saline soil large as well as soils with a small slope are preferred.

By analyzing the three possible scenarios for the management of waste water produced by factories of olive oil processing, we come to the conclusion that the third alternative is the best alternative. Waste treatment in a large central plant is not considered as a good alternative, because of the large distribution of factories significantly increases the cost of collection and transportation, even if this is done through pipelines or through special means. The volume of the waste water that these units are designed to handle is very large, this necessarily increases the cost of installing the treatment units. On the other hand, the production of olive oil is a seasonal product that lasts approximately four months. The second scenario, as well it is not considered because each mill has to cover the cost of the treatment unit individually, the cost of installation and maintenance. The mills prefer the low cost treatment. Also this scenario is necessarily effective in disposing of wastewater and thereby creating droplets pollutants for each factory. As a conclusion, the third alternative is seen as the best management plan, as the volumes of wastewater are manageable, the scattered points of pollution are reduced for each factory if they would do the treatment individually and also, thanks contribution of several factories and with the help of the relevant authorities, one can be selected most effective treatment technique.

However, despite encouraging results from these investigations, OMW is still discharged in to the environment without any treatment in many developing countries such as Albania. The increase of the number of oil extraction units starts to make the environmental problem of OMW more visible. Indeed, in many regions OMW is stored in ponds, where evaporation is very limited, generating volatile malodorous compounds, threatening the groundwater and decreasing the surface of arable land because new ponds are dug each year to hold new OMW.

Conclusions and Recommendations

Olive oil production is an important global economic sector, as more and more countries are committed to becoming dominant in this sector. This sector is considered among the most important sectors in Albania, apart from the fact of the involvement of about 1/3 of Albanian farmers, but also of families engaged in the production of olive oil for personal consumption. The main areas that cover the total production of olive oil production in Albania are the counties of Fier, Berat, Elbasan and Vlora.

However, the production and processing of olive oil is accompanied by negative and serious impacts on the environment if they are not managed and treated in the right way. Albania faces many problems regarding the management and treatment of waste produced at the end of the olive oil processing process, due to high costs for the installation of treatment units, negligence, lack of knowledge about the effects on the environment, as well as the absence of normative acts for the treatment and use of this waste.

The waste treatment techniques formed at the end of the olive oil processing process, if used individually, are inefficient and insufficient for the complete neutralization of the waste, so their combination is preferred. The most widespread, low cost and satisfactory result main technique is the combination of evaporation tanks together with the addition of Ca(OH)₂ for neutralization of olive oil waste waters.

As a result of the calculation the values of the OMWWs produced be the different types of OOM for Albania and for Elbasan country, are very high, 149,815 m³ wastewater in Albania, and 24,285 m³ olive oil mill wastewater.

The olive factory that is taken as a case study in this paper uses the anaerobic biological treatment technique with septic tanks. Although the method is not more effective than the other techniques, it is a satisfactory method due to the fact that most factories in Albania freely discharge these wastes into the environment. According to the data from the Director of the Environment for the Elbasan Municipality, only 10% of the district’s factories treated waste, while 90% of them did not.

By analysing the three possible scenarios for the management of waste water produced by factories of olive oil processing, we come to the conclusion that the third alternative is the best alternative. The third alternative is seen as the best management plan, as the volumes of wastewater are manageable, the scattered points of pollution are reduced for each factory if they would do the treatment individually and also, thanks contribution of several factories and with the help of the relevant authorities, one can be selected most effective treatment technique.

Drawing up management plans for the waste produced at the end of the olive oil processing process and their economic use, according to the best alternative proposed for the construction of small units for the management and treatment of olive oil mill waste located next to each other depending on the extension area.

Strengthening the laws and regulations for the discharge of untreated wastewater into the environment and taking appropriate measures against operators who neglect the importance and environmental impact caused by the discharge of this untreated waste into the environment.

Extent of subsidy policies not only in the processing of raw materials but also in the installation of waste treatment units significantly reducing the high cost of total plant construction and helping operators.

Drafting of design and construction criteria for olive oil processing mills, implementing the norms and values allowed by neighboring countries and adapting them to the situation and status in Albania.