With the adoption of the "two-phase" olive oil extraction system from the 1990s onwards, the by-product obtained was essentially "wet" pomace with moisture contents of over 65% (Figure 1).
This change in extraction technology, from the previous "three-phase" to "two-phase" process, eliminated the environmental problem of wastewater, which was difficult to treat, but created a technological problem because it gave rise to a by-product, the "wet" pomace (which resulted from not separating the vegetation water from the olives), which could not be used directly. To make it possible to use these pomace, it was then necessary to build large drying facilities, which remove the moisture in Trommel-type dryers, obtaining a "dry" pomace at the end of the process, with around 15 to 20% moisture. These drying plants have become the main beneficiaries of this change in the olive oil industry process, earning revenue by paying the mills for each ton of "wet" pomace delivered, by selling the stones they manage to extract from the pomace before drying (Figure 2), by selling pomace oil extracted with solvents from the "dry" pomace and by subsequently selling the "extracted" pomace for burning in boilers, for the concentrated animal feed industry or for the production of organic fertilizers.
The revolution of the new 4.0 oil mills
Aware of this loss of revenue, the olive oil mills began, initially, to remove the olive stones and introduce another decanter into the extraction circuit (the famous "repasso" line/decanter), in order to remove as much oil as possible from the "wet" pomace before sending it to the industrial dryer, which now receives "exhausted" pomace. In this way, in addition to selling quality olive oil (virgin or extra virgin), the mills began to sell stones to burn in boilers and lampante oil obtained on the "repasso" line that has to be refined.
In the most modern mills, with so-called 4.0 technology, this "pass-through" line has already been replaced by decanters with NIR sensors and Artificial Intelligence software that allow the decanter's operating parameters to be adjusted in real time, without human intervention, in order to reduce the loss of fat to the "wet" pomace as much as possible (Figure 3).
More recently, larger mills have started to use part of the pomace in organic compost, reducing the amount of "wet" pomace sent for drying. The compost produced in compost heaps results from a mixture of wet pomace (up to 50% of the total heap), olive leaves (also obtained at the mill during the olive cleaning process), olive tree pruning waste and animal manure (a maximum of 30% of the mixture). However, several mills in Portugal are studying technological solutions that would allow them to stop sending the "wet" pomace to the pomace dryers and extract the maximum revenue from it, in facilities adjacent to the mills. We're talking about biogas production, to be produced in biodigesters, which would obtain biogas (with a high biomethane content) by biodigesting the "wet" pomace, which would then be injected into the national natural gas grid. Another possibility under study is the construction of facilities for the bioconversion of "wet" pomace, using insect larvae, into high-value organic fertilizer. With these solutions, medium and large olive oil mills will once again be the beneficiaries of the revenue from the by-products they produce, to the detriment of olive pomace dryers (...).
Source: Voz do Campo, 7 August 2024
Comments