Olive farming generates a range of by-products from pruning and harvesting, as well as wastewater and materials from the olive oil extraction process and the pomace (skins, pulp and seeds). These organic waste materials contain compounds which can be either detrimental or beneficial to the environment, depending on how they are managed.
For example, olive mill wastewater contains polyphenols that can reduce beneficial microbe activity in soil, but when treated this waste can produce biodegradable polymers for packaging. Similarly, when left untreated, olive pomace can ferment to produce methane and pollutants, but by contrast it can also be converted to biochar and used to improve soil quality and store carbon. Residues from pruning and harvesting can be used as biomass to replace fossil fuels.
These sustainable uses of olive farm waste restore, renew or revitalise their own sources of energy and materials, wasting as little as possible. This Saudi Arabian example may have relevance for the EU’s second circular economy action plan, which supports initiatives to minimise waste and keep waste resources within the EU economy.
The Aj-Jouf region in northern Saudi Arabia has become a key area for olive cultivation, producing two-thirds of the country’s total. The region contains high density olive orchards and modern irrigation systems that maintain olive production in arid conditions. Amongst this high-intensity agriculture there is a need to consider the sustainable use of by-products. This new study evaluates not only the environmental benefits but the economic contribution and the impact on soil quality of re-using olive by-products through composting and bioenergy production.
The researchers focused on farms with two types of olive – Arbosana and Arbequina. They measured the weight of pruning and harvesting residues, and the amount of olive pomace, and calculated sustainability values, including the efficiency of waste reduction and re-use, energy-generation potential, the reduction in environmental impact, the economic gain and soil improvement.
The study estimated that on average the total biomass, including pruning and harvesting residues and olive pomace, was 10,675 kg to 11,175 kg per hectare. The amount used in composting and bioenergy production was 6,958 kg to 7,283 kg per hectare, producing an efficiency figure of 63% to 67%. This efficiency rating was highest in harvesting residues, indicating that high-density olive orchards have the potential for repurposing their by-products efficiently.
Focusing on bioenergy production, the study estimated that the residues from harvesting and pruning could produce 72.6 GJ per hectare, whilst the pomace could produce about 24 GJ per hectare. This brings the total power potential for every hectare of olive farm to 2.6 million KWh, which is slightly less than the annual consumption of the average home in Saudi Arabia. This was calculated assuming there would be no loss in the conversion of recovered biomass and demonstrates that olive waste is a valuable renewable energy resource.
On environmental impacts, the carbon footprint per hectare was typically reduced by 50-60% via the use of olive farm by-products in compost and bioenergy. This was due to the avoidance of open burning, the capture of carbon in compost and potentially biochar, and the replacement of fossil fuels. For example, each ton of dry olive biomass used instead of fossil fuels can avoid about 1.5 tons of CO2 emissions. If more by-products were used in this way the positive environmental impacts would be even greater. The researchers’ efficiency calculations estimated that 35% remains under used.
Production of bioenergy and compost from olive by-products also offers financial benefits. The biomass from pruning residues along with the olive pomace can be converted into heat or electricity or sold as biomass fuel such as wood chips or pellets. The study estimated this could produce about $250 per hectare. This is relevant to the recently adopted EU 2026 Circular Economy Act, which aims to establish a single market for recycled and re-used waste materials, as well as the recently adopted Bioeconomy Strategy, which aims to make “better use of Europe’s biological resources, scientific excellence and industrial base to decarbonise our economy and replace fossil-based materials and products.” according to the Bioeconomy Strategy document.
Furthermore, olive waste compost can improve soil fertility and offset the cost of artificial fertilisers to save about $100 per hectare. Considering the collection, processing and application costs, the total profit from both sources was estimated to be about $70 per hectare. Although this seems relatively modest, the practice looks economically sound and self-sustaining.
Lastly, the study assessed improvements in soil quality and waste reduction and estimated that the use of olive by-products would reduce waste by 35% and increase the amount of soil organic matter from 1.3% to 1.5%. This is a crucial ingredient in soil health, as it improves structure, water retention and nutrient availability. The researchers note that future work could focus on optimising the logistics of residue and pomace collection and improving the overall energy conversion efficiency of the waste products.
Beyond bioenergy and compost, there is potential for other olive waste re-uses, such as chemicals derived from plants. The EU is financing projects which aim to create a biorefinery where waste such as olive pomace, olive stones and residues of other nuts are recovered to make molecules for use in nutritional supplements and cosmetic industries.
The results of this study provide compelling evidence for both the environmental and economic advantages of using olive industry waste within a circular bioeconomy framework which recaptures waste as a resource.
Reference:
Alharbi, A.; Ghonimy, M. Environmental benefits of olive by-products in energy, soil, and sustainable management. Sustainability 2025, 17, 4722. https://doi.org/10.3390/su17104722