Baiba Brice: Digestate management for sustainability

With the approval of the European Green Deal and featured initiatives developed within its framework, increasing importance is devoted to aspects such as efficient resource management and use, the role of renewable energy in promoting energy independence, healthy soils and the implementation of circular economy principles in various sectors. In turn, the HELCOM Regional Nutrient recycling strategy emphasises that nutrient recycling on land and losses to the sea should be improved to reduce the harmful impact on the Baltic Sea.

One sector that impacts nutrient leakage is biogas production, which has been developed for decades as part of sustainable energy and resource management strategies.

Biogas production in the Baltic Sea Region is essential as a source of renewable energy and an effective way to process biological waste. It promotes energy independence, reduces greenhouse gas emissions, and helps process organic waste from agriculture, the food industry, and household waste, thus promoting sustainable resource circulation. However, the biogas production process produces digestate – a nutrient-rich by-product that, if properly managed, can become a valuable resource for improving soil fertility and sustainable agriculture. The high-quality use of digestate helps to effectively close the nutrient cycle, reducing the need for synthetic fertilisers, and significantly reduces environmental pollution, especially in the Baltic Sea region, where excessive nutrient discharge into the waters is a significant ecological problem. Therefore, digestate management and quality assurance are becoming an essential aspect of the region's sustainable development policy.

To ensure effective digestate management, it is crucial to consider several aspects which have an impact on sustainability and the environment:

• composition – in biogas production as feedstock, different organic materials such as agricultural, food, industrial, and sewage sludge are used. It is essential to ensure that feedstock is of proper quality and does not include harmful substances such as heavy metals as they afterwards occur also in the digestate;
• Nutrient leakage and pollution—digestate mismanagement can contaminate soils and water, contribute to eutrophication, and emit greenhouse gases. National legislation determines how to ensure the proper incorporation of digestate into the soil, which must be followed during its storage to avoid soil and air pollution.

However, one of the effective ways to ensure the safe use of digestate is to establish quality assurance systems. The digestate quality assurance system aims to create a framework and requirements for biogas plants that use raw materials in the anaerobic digestion process and for the digestate obtained during the relevant process to ensure its compliance with specific safety and quality indicators, as a result of which the digestate acquires end-of-waste status and can be safely used as fertiliser.

The establishment of a quality assurance system has several objectives:

1. to create a framework and system for the circulation and use of processed nutrient products;
2. to ensure the quality of processed nutrient products;
3. to ensure the traceability of raw materials and the transparency of the raw material chain;
4. to promote compliance with the principles of the circular economy;
5. to increase awareness of processed nutrient products and their quality;
6. to inform the end user about how, where and from which raw materials processed nutrient products are produced.

In several Baltic Sea region countries, digestate quality assurance schemes have already been in place for several years, contributing efficiently to the effective nutrient management in agriculture and landscaping, and they are developed according to the specific country's legislation and needs. Digestate quality assurance systems are in place in the Baltic Sea region in Germany, Finland, Sweden and Estonia. In Latvia, the digestate quality assurance system proposal was developed in the framework of the Interreg Central Baltic programme project "Sustainable biogas", but it is not operative.

However, to enhance digestate sustainability in the Baltic Sea Region, it is essential to develop harmonised standards for digestate quality assessment. This approach would maximise digestate's agricultural benefits while minimising environmental risks. Also, common standards and management policy would change the public perception as misconceptions about digestate safety and effectiveness prevail over its environmental benefits.

The Baltic Sea Region can advance towards more sustainable nutrient management by implementing standardised regulations, improving processing technologies, and fostering cross-border collaboration. Future efforts should focus on bridging policy gaps, encouraging innovation, and ensuring long-term environmental protection.