## 1 Introduction  
As the world's population grows and people increasingly prefer to be self-sufficient, growing vegetables presents new challenges. We must not only produce enough food to nourish people, but we must also fulfill the increasing demand for high-quality, value-added food products. However, growing value-added vegetables is challenging because many methods studied require large energy resources [1, 2]. Vegetable yields depend directly on the quality of the seedlings, so it is crucial to create optimal conditions for good-quality seedlings to grow, which later have the potential to produce a high-quality harvest [3, 4]. One of the most important elements in seedling production is the substrate and the nutrients it contains. At the same time as the world is striving for quality yields, it is also seeking new sustainability solutions. One such solution is the substrate. Peat is widely used for growing seedlings, but its resources are decreasing because of peatland degradation, and we need to find alternative substrates that are both sustainable and useful for plants [5, 6]. To achieve sustainability and reduce the amount of waste, waste recycling is increasingly being used as an alternative. Energy and biogas are extracted from them [7,8]. After extracting biogas, the digestate remains as a waste. But for over two decades, effective ways of using digestate have been sought, and it has become a useful addition rather than a waste [9, 10, 11, 12, 13, 14]. Agronomic research on digestate has expanded widely [15,16]. Digestate has become an excellent tool for enriching the eroding and disappearing soil and restoring its fertility. Digestate is rich in composition, so prospects are being sought to use it as a fertilizer [17, 18, 19, 20]. In recent years, there has been an increase in research on the effect of digestate on vegetable cultivation. The research includes field-grown vegetables and greenhouse-grown ones, such as tomatoes [21, 22, 23]. Solid digestate is used as an addition to the substrate, peat, or liquid--as a liquid fertilizer. Different proportions of digestate use affect tomato growth, yield, and fruit quality. It is important not only to produce an abundant harvest, but the fruits must also be of high quality and have an added value [24, 25, 26]. Studies show that replacing mineral fertilizers with digestates results in the same or even higher yields or using it together--much higher tomato yield [24,27]. Also, digestate can increase fruit color, firmness, and soluble solids [26]. Furthermore, research on tomato plants shows that digestate impacts antioxidant activity and plant growth. Digestate increases tomatoes height, stem diameter, and chlorophylls [27]. As a vegetable, tomatoes have high value for human health because they contain useful bioactive molecules [28]. The fruit contains carotenoids, vitamins, flavonoids, and phenolic compounds. These bioactive molecules are key elements in the plant's antioxidant system. They can inhibit cellular proliferation, modulate enzyme activity, and inactivate damaging radicals [29]. Higher levels of antioxidant compounds are desirable not only for human health reasons but also for their ability to protect the plant from oxidative damage, which may result in a loss of efficacy followed by commercial and economic loss [30]. Mineral fertilizers are increasingly being replaced by other alternatives to achieve sustainability. One of the options for sustainable cultivation was the use of compost [31, 32, 33]. Research indicates that in certain situations, the yield and quality may decline when compost is used instead of mineral fertilizers, as tomatoes require a high nutrient content in the substrate [21, 24, 26, 34, 35, 36]. Digestate showed very good prospects not only for tomato cultivation but also for lettuce under salinity stress [37]. Various wastes for biogas production produce digestate, which is increasingly used as fertilizer in agriculture. Digestate studies are mainly focused on the yield and its external quality.