Olive oil waste storage times impact final compost yields

UCO studied, for the first time, how Alperujo storage times affect the subsequent composting process, taking into account both the quality of the product and the emission of greenhouse gases and microbiological activity. The work is published in the Journal of Environmental Management.

Alperujo is the main by-product of olive oil extraction. This waste has an important environmental challenge due to its high organic load and its presence of phenolic compounds, which can contaminate soil and surface water. However, when the circular economy comes into play, Alperujo can have a second life as a bunch, allowing waste to be converted into a new value of value.

In order to better understand the composting process in which Alperujo becomes a safe fertilizer for fields, molecular biology of stress response mechanisms and waste bio-engineering: green engineering at the University of Cordoba of groups has joined forces to check the Alperujo storage times.

After the extraction of the oil, the Alperujo is stored in support ponds until it undergoes treatment; In this case, composting to produce an organic fertilizer. “We studied how two different storage periods (3 and 6 months) affected the parameters during subsequent composting, such as yield, greenhouse gas emissions, degradation of phenolic compounds and the microbial community,” explained Francisco Javier Ruiz, principal of the study, set of Marina Barbudo.

After studying what is happening on a real scale, the results have shown that short -term storage (3 months) improves compost yields; In other words, a larger amount of fertilizer is obtained. In addition, it generates lower greenhouse gas emissions during composting.

“In the two periods, the phenolic compounds are effectively removed, which is very important for the final product (the fertilizer) because these compounds are phytotoxic and can be harmful when applied in the fields,” said José Alhama, another of the authors.

“The reason for the elimination lies mainly in the high temperature affected by the mass of the composable material, reducing the concentration of phenolic compounds and disinfecting the product,” added researcher Maria Del Carmen Guérrez.

Another innovation is the study of the microbial community during the process. “An innovation analyzed the microbial community, identifying it in a taxonomic way and saw its functional capacity. Identifying this analysis in storage times was something that had not been assessed,” said researcher Maria Ángeles Martín Santos.

Metagenomic analysis revealed differences in the bacteriom of raw material according to its storage time, variations which also became obvious during composting.

“The thermophilic stage (the second composting phase in which there is a large increase in temperature) caused the selection of thermophilic bacteria (those which resist high temperatures), which manage to degrade organic matter,” continued Marina Barbudo.

According to Carmen Michán, “this knowledge makes it possible to modify changes. If we know that a microorganism promotes the degradation of certain compounds, if at some point, we do not want the end result, for example, a lot of phenols, it can help add certain microorganisms.”

In this way, composting can be optimized. This study characterizes what is happening at each stage, allowing us to take advantage or modify the conditions to obtain maximum yields with less environmental impact.