Suspension fertilizers based on alternative raw materials – the key to sustainability and closed nutrient cycles

Abstract

The rapid, high increase in production costs and prices of mineral fertilizers leads to a reduction in their use by farmers, while fertilizer manufacturers consider the use of alternative raw materials and reducing the energy consumption of fertilizer production processes. Given these circumstances, special attention is warranted for suspension fertilizers. The manufacturing of suspension fertilizers is simplified and less energy intensive in comparison with solid fertilizers. This is achieved by omitting certain production stages such as granulation, drying, sifting, which usually contribute to more than half of the production costs. This paper presents the production procedure of suspension fertilizers tailored for cabbage cultivation, utilizing alternative raw materials such as sewage sludge ash and poultry litter ash. The final products are thoroughly characterized. The obtained fertilizers were rich in main nutrients (ranging from 23.38% to 30.60% NPK) as along with secondary nutrients and micronutrients. Moreover, they adhere to the stipulated standards concerning heavy metal content as outlined in the European Fertilizer Regulation. A distribution analysis has showed that suspension fertilizers contain nutrients in both liquid and solid phases. This arrangement facilitates their easy availability for plants and subsequent release upon dissolution in soil conditions. To assess process consistency, the production of the most promising fertilizer was upscaled. A preliminary technological and economic analysis was also conducted. The method of producing suspension fertilizers using alternative raw materials is a simple waste management solution offering nutrient recycling with the principles of circular economy. This approach not only encourages nutrient recycling but also curtails reliance on imported raw materials.