29 Jul A Review of: Recycling Solid Waste from the Olive Oil Extraction Process RIRDC Pub. No. 08/165
Completed by John Barton, Director – Charton & Bang
Document Contents
The document under review was produced by the former Rural Industries Research and Development Corporation (RIRDC), now known as Agrifutures Australia. This document describes the process and results of a trial to establish whether composting olive mill waste (OMW) removes the negative biological properties of raw OMW. This material contains two phytotoxic (toxic to plants) compounds; phenols and volatile fatty acids (VFA). VFAs are present in any similar organic waste that is fresh and moist. They are the breakdown compounds of initial microbial decomposition of organic matter. In high concentrations they are toxic to plants. Phenols are more specific to organic materials with a high concentration of secondary metabolites, such as eucalyptus leaves and olives. High concentrations of these compounds have antimicrobial properties and can potentially be toxic to other forms of life. The application of raw OMW to land creates a situation that can be detrimental to plant health and the health of the soil. This leaves olive processors with a waste that can have negative consequences if spread back in the orchard, or that can cause unpleasant odours or environmental issues if stored improperly.
This document proposes composting as an appropriate method for removing the negative properties of OMW and creating positive qualities during the process. Phenols and VFAs are organic molecules, meaning they are subject to microbial degradation during composting. Composting will change their chemical structure and therefore their properties. This document describes a trial where OMW from 2 and 3 stage olive extraction processes is composted with manure and straw. As part of this trial they describe a method they have developed for measuring phenols so that they can establish if the composting was successful in removing them. The results are that phenols and VFAs are removed by their method of composting, that humates and humic acids are created, and that the finished material is beneficial to the growth of radish seedlings. It also gives a nominal budget for the estimated costs of production, excluding water, labour and the value of the finished product.
Document Review
This document is as a scientific paper that uses a formal language and structure that may not be familiar to all olive growers. It may be difficult to extract the relevant information that could be used to inform on-farm practice. It does not provide any data on whether positive results should be expected from application of the compost to olive orchards. It does not suggest appropriate application rates or application methods. It only provides the specific information that it is possible to compost OMW to successfully treat the waste. Despite the limitations of this document, this information is extremely valuable for the management of OMW in Australia.
Reviewed from the perspective of a professional composter, the trial described in this document appears to use a relatively simple and straightforward composting method that is accessible to most olive producers. It does not however provide adequate instructions on how to perform this composting process. In addition, the budget provided is inaccurate. It lists ingredient costs far higher than could be achieved at an agricultural scale and omits the cost of water. It also omits the cost of labour and machinery, which are significant in compost production. However, once the costs of ingredients are more appropriate, and labour and machinery costs are added, it is likely that the total will remain similar. The budget should also include the value of the finished product when used on farm to properly show the true costings of treating OMW by composting. Throughout the document there are comments demonstrating unfamiliarity with large scale composting based on similarly misguided interpretations and results found in individual published scientific papers. If these comments are ignored in favour of the actual results as the focus, the document is still useful and relevant.
Released in 2007, this document is now 11 years old. Since this time there have been a swathe of further research across the world into the benefits of composting olive mill waste. Some of this research specifically addresses the beneficial reuse of composted OMW back into olive orchards. Gómez-Muñoz et al (2012) demonstrated increases in soil carbon and phosphorus availability. They also demonstrated that there were reduced soil losses of nitrogen through leaching and loss as gases. Regni et al (2017) showed that composted OMW increased soil carbon and olive yield with no reduction in quality when compared to application of raw OMW. Cucci et al (2013) demonstrated improvements in soil structure after application of composted OMW, which has strong implications for increases in soil water storage capacity.
There now exists a body of work that provides a powerful case for recycling OMW. Composting OMW provides an option that successfully treats a problematic waste, can be performed for a moderate cost, and provides an end product that is beneficial to orchard health. However, specific details of application methods, application rates and the level of response that should be expected in Australian conditions are sparse.
Despite the research that has followed this document, it still remains relevant. It shows that OMW can be composted successfully under Australian conditions for a moderate cost. Its findings have not been disproved, but rather added to. It should not be modified or removed, but its benefit to olive producers could be improved by an addendum and further local research.
Further Documents
This document has a laid a foundation for composting OMW in Australia that needs to be built upon. The following additional documents are recommended:
- An addendum to this document, that describes in plain English the contents, outcomes and implications of this document
- A practical guide to composting OMW in Australia
- A research/demonstration project that defines the agronomic benefits of applying composted OMW in Australia. This should include appropriate application rates and methods of composted OMW along with costs and projected profits
- Following the results of document #3, a practical guide to applying compost in olive orchards in Australia
Conclusion
This document has retained its relevance in the 11 years since its production, but it needs to be paired with additional research and publications in Australian conditions. There is sufficient research around the world to indicate a high confidence of success in composting OMW and applying it to olive orchards. Local research into the use of composted OMW and practical guides on how to achieve this will complete the case for widespread adoption of composted OMW as a waste treatment method and soil amendment for olive orchards.
References
Beatriz Gómez-Muñoz, David J. Hatch, Roland Bol and Roberto García-Ruiz, 2012. The Compost of Olive Mill Pomace: From a Waste to a Resource – Environmental Benefits of Its Application in Olive Oil Groves
Luca Regni, Luigi Nasini, Luana Ilarioni, Antonio Brunori, Luisa Massaccesi, Alberto Agnelli and Primo Proietti, 2017. Long Term Amendment with Fresh and Composted Solid Olive Mill Waste on Olive Grove Affects Carbon Sequestration by Prunings, Fruits, and Soil. Front. Plant Sci, https://doi.org/10.3389/fpls.2016.02042
Download the review here