# Reuse of Spent Coffee Grounds: Alternative Applications, Challenges, and Prospects--A Review
## 3 Fertilizer from SCGs  
SCGs can be used to produce a tablet fertilizer. In a study of SCGs mixed with biomass ashes, [PERSON] et al. (2016) showed that the best of the binders tested was food-grade gelatin, which allowed for the materials to be combined for safe storage and transportation. In addition, food gelatin ensures the slow release of organic compounds from the resulting tablet fertilizer. Tablet fertilizer can replace expensive commercial fertilizers. The use of conventional fertilizers is associated with less uptake by plants, resulting from the penetration of nutrients into deeper parts of the soil. Tablet fertilizers save the time associated with systematic fertilization and eliminate the loss of unabsorbed compounds by the plants. In addition, tablet fertilizer is an ecological alternative that is not only safe for the environment but also allows for a practical way to manage used SCGs. It contributes to improving the fertility of horticultural soil, especially for plants growing in pots and containers [20]. The use of gelatin as a binder increases the cost of the fertilizer. SCGs may contain caffeine and other compounds potentially harmful to certain plants, and their nutrient content is limited compared to commercial fertilizers. Collecting and processing SCGs on a large scale requires an efficient logistical system, which can be challenging. The benefits of using SCGs as fertilizer need to be validated through field studies. Future research should consider the industrial scale of the process. In the study by [PERSON] et al. (2021), SCGs were added to peat to create a mixture that served as a substrate for cultivating Brassica seedlings, including cabbage, cauliflower, and broccoli. The addition of 10% SCGs to peat showed a negative effect on plant growth, as it reduced the height of the plants and the number of leaves and increased the average germination time. It also affected a decrease in stomatal conductance of broccoli and cabbage and an increase in chlorophyll content. Seed germination was stimulated at 2.5-5% addition of SCGs for cauliflower and at 2.5% addition for cabbage. Plant biomass and number of leaves increased with 2.5% SCG addition for broccoli and cabbage and remained at the level of the control sample for cauliflower. The addition of SCGs also affected mineral accumulation in Brassica plants. It caused an increase in nitrogen, potassium, and phosphorus content and a decrease in magnesium and iron content. A study [PERSON] et al. (2021) showed that the addition of up to 5% SCGs to peat substrate can be a good biostimulator of seed germination and partially replace peat during Brassica seedling production. SCGs are a good waste material that effectively affects the fertility of growing media. Disadvantages of using SCGs for Brassica seedling production include the need to use an exact amount of coffee waste so that it does not exceed 5% content, which can be a practical difficulty. The use of grounds also requires careful processing and stabilization to avoid potential problems associated with the presence of caffeine residues or other substances that can affect plant growth and health [21]. In a study by [PERSON] et al. (2019), the effect of SCGs on the elemental content of lettuce was determined. The addition of SCGs to the substrate caused an increase in essential elements such as iron, cobalt, manganese, and zinc, as well as toxic elements aluminum and arsenic, without exceeding toxic levels. The addition of SCGs also helped inhibit the plant's uptake of nitrogen and cadmium from the soil. Lettuce that grows on a medium with SCGs added is organic and contains good nutritional value [22]. The use of SCGs in lettuce cultivation has advantages, such as increased levels of beneficial elements and other bioactive compounds. Although the presence of heavy metals does not exceed toxic levels, their presence may raise concerns regarding human consumption. The inhibition of nitrogen uptake by the plant could negatively affect its growth.