Assembly of European Horticultural Regions

EU projects

AREFLH is a partner of Waste4Soil project “Turning food waste into sustainable soil improvers for better soil health and improved food system”.

The project aims at developing applicable recycling technical pathways to transform Food Processing Residues (FPR) into improvers, through a circular, system and multi-actor approach. All food chain actors are involved at the regional level, thereby closing specific loops (nutrients, organic matter, water).


This month's article is about an article published by the University of Ljubljana, a partner of the project,  on “Microalgae Production on Biogas Digestate in Sub-Alpine Region of Europe—Development of Simple Management Decision Support Tool “ 


The large-scale cultivation of algal biomass in wastewater streams is an attractive technology for putting circular bio-economy theory into practice. Algae extract and recycle nutrients, organic carbon, and minerals that would otherwise be lost to the environment. They also sequester CO2 from the atmosphere. In wastewater treatment plants, they reduce energy costs by 50% by providing bacteria with the oxygen needed for biological treatment.

In turn, wastewater enables more economical large-scale production without the need for large quantities of quality water and expensive commercial growth media. Large-scale algal cultivation offers an interesting opportunity for multiple industries and agriculture, as algae can grow in a variety of waste substrates, and the biomass produced can be utilized for a variety of products, providing additional financial streams, instead of costs, for wastewater disposal or conventional treatment. 


Recently, microalgae cultivated in wastewater have been well utilized in agricultural products. Organic fertilizers from microalgae are available in the market, and their beneficial effects on soil and plants have been demonstrated on many occasions. Research on microalgae shows promising results when using microalgae derived products in agriculture: microalgal biofertilizers improve soil health; microalgal bio stimulants have positive effects on development, growth, and yields of crops and microalgae may be considered potential biocontrol agents—biopesticides. 


While digestate can be used directly as an organic fertilizer due to its high nutrient content, it presents logistical and storage challenges, associated with high greenhouse gas emissions. In addition, the composition of digestate can vary widely, making its application in fields a challenge for farmers. Algae cultivated in digestate can help stabilize it by incorporating nutrients into their biomass. The stabilization allows for easier storage, transport, and application, reducing the environmental footprint. Green microalgae have been widely researched for the treatment of liquid digestate and are efficient in removing nutrients and organic contaminants from this source. 


Microalgae have the capacity to utilize dissolved carbon dioxide and nutrients like ammonia, nitrates, nitrites, and phosphates. This characteristic renders them highly effective in treating liquid digestate; for example, the potential to reduce nitrogen, phosphates, and total COD by up to 70%, 57%, and 95%, respectively, was demonstrated with microalgae consortia, and even higher efficiencies are regularly reported. 


Open algal ponds are a low-cost technology, and their maintenance is relatively simple. They can be integrated into the existing technology system as side-streams without major restructuring, which makes them appealing to industrial operators. In the case of biogas plants, ponds can be installed on-site to treat the digestate, which significantly reduces the costs and environmental impact. Nevertheless, in the sub-alpine climate, the operation of the algae in pond culture is hampered by the low temperature, fog, and low solar irradiation in the colder months, typically resulting in the low conversion of digestate nutrients to algal biomass, which is not attractive to biogas plant operators. 


The main obstacles in scaling up biomass production in the conventional system are high processing costs and low efficiency; therefore, the use of digital technology could improve productivity effectively and efficiently manage microalgal biomass production. The monitoring and control of parameters such as pH, T, and nutrient status is crucial in microalgae culture because it not only increases the production and quality of microalgae biomass but also prevents critical conditions for the culture that may jeopardize cultivation. Easy-to-use monitoring and control, coupled with a decision support tool for microalgal cultivation, could be of great assistance to microalgal facility operators. 


Click here to read the complete article 


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This project receives funding from the European Union’s Horizon Europe Research and Innovation Programme under Grant Agreement Nr. 101112708.

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