There is a lot of talk about innovation and innovative thinking. However, we would like to focus on technological developments at a high scientific level that have significant importance for people and for the circular economy. Such innovations were presented by the research teams from Sofia University working within the Clean&Circle Center of Competence at the international conference “Kliment’s Days,” held on November 6–7, 2025.

Using cold plasma, wastewater from biogas production processes at the wastewater treatment plants in Sofia (“Kubratovo”) and at WWTP “Ravda” was treated. The achieved effect includes the complete destruction of pathogenic bacteria and the reduction of overall toxicity. As a result, this wastewater (digestate) is transformed into a suitable multi-effect liquid fertilizer for agriculture. This fertilizer enriches soils with biogenic elements, helps maintain moisture, and the long-lasting residual compounds formed during plasma treatment stimulate seed germination and plant growth, while also activating the natural detoxification processes in the soil.

The development of this innovation is the work of a team of experienced experts in environmental biotechnology and plasma technologies, with young researchers such as Yoana Sofronieva and Lyubomira Gelanova participating in its experimental implementation. In this way, through “learning by doing” from the very beginning of their master’s studies, young scientists are encouraged to

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