A large consumption of water that produces large volumes of wastewater with brine
The EU produces 36% of the world's table olives, with the sector being an important contributor to the economies of Spain and Greece, as well as Italy, Portugal and France. The average annual production in the EU is approximately 841,500 tonnes of total world production of 1,684,700 tonnes (2015, IOC).
The total European production of table olives has increased by 132% in the last twenty years, especially due to the increase in the productivity of agricultural land. The olive groves are concentrated in Spain (50%), Italy (26%) and Greece (22%), especially in the southern areas.
The trend of positive growth in the production of table olives entails a high environmental cost: a large consumption of water that produces large volumes of wastewater ranging between 0.5 liters and 6 liters per kg of processed olives. Thus, each year an average of up to 11.7 million tons of wastewater and more than 2.2 million tons are generated in the EU as a result of the processing of table olives. In addition, this sector is located in the Mediterranean basin, where episodes of water scarcity are expected to be more frequent due to climate change.
The process of producing table olives generates different wastewater in each of the stages of production:
The degreasing process generates bleach and wash water.
The fermentation process produces brines (fermentation and packaging).
The treatment of wastewater from this industry is extremely complex due to its composition and the seasonality of the effluents generated, the bleach and washing from November to December and the brines from January to June.
Conventional treatments, based mainly on biological technologies, are not effective due to the high conductivity, free NaOH and high COD, especially the presence of polyphenols that inhibit biological activity.
Currently, all effluents from this industry accumulate in open evaporation ponds. Periodically, the state of conservation of these rafts should be inspected and, if necessary, cleaned. The sludge generated, after being treated by a conventional evaporator, is disposed of in landfills. However, poor practices in the construction of ponds and the preservation of evaporation ponds carry a high risk of contamination due to the leakage of waste and migration to groundwater and deep soils.
In addition to the aforementioned rafts, the most common waste management option for brines is the discharge into the sea, on land surfaces or the injection of deep wells, but this leads to an increase in the salt content of the water masses, and therefore, will generally have a negative environmental effect. These harmful practices produce malodorous gases due to putrefactive or methanogenic bacteria under uncontrolled environmental conditions. The accumulation of wastewater from the preparation of table olives implies serious environmental impacts and dangers:
High occupation of the land by natural evaporation ponds, sometimes located in forests or natural places. It is estimated that around 158.51 Ha (equivalent to 230 football fields) are needed annually for the accumulation of wastewater from table olives in the EU.
Very low resource efficiency, losing valuable elements such as water, salt and organic compounds present in the brines.
CO2 emissions caused by the use of gas evaporators to reduce the volume in the accumulation ponds during the generation of the brine peak.
Accumulation of uncontrolled sludge at the bottom of the pond that reduces its capacity each year and must be managed separately. This sludge is sent to landfills.
Increased risk of brine spills due to overflows due to high intensity rain caused by climate change.
Why is LIFE SOLIEVA project necessary?
The development and adoption of technologies to recover valuable resources from waste is one of the main priorities of the EU Commission. However, it is necessary to develop and implement water recovery processes and valuable compounds (inorganic salts, polyphenols, etc.) of the brines, not only to reduce the environmental impact, but also to increase the economic sustainability of the sector at the same time the use of natural resources is reduced through the development of circular economy schemes.
The table olive sector, as one of the main producers of brine in the agri-food sector in Europe, faces environmental challenges: high water consumption, complex composition of the liquid waste generated and recalcitrant organic matter. Therefore, it is crucial to foster the adoption of an innovative and profitable solution that transforms the sector into an important source of natural resources with an eco-friendly value.