Review Paper on the Possibility of NPK Fertilizer Production from Sewage Sludge

Circular Economy (CE) package accepted by the European Union (EU) in December 2015 promotes close-loop flows of materials. The main targets provided in the documents refer to the prevention of waste landfilling, efficient use of resources and energy, as well as re-use waste and by-products. Sewage sludge�residue from Waste Water Treatment Plant (WWTP)�has a great fertilizer potential and should be recycled in line with the CE strategy. Sewage sludge usage for agricultural purposes seems to be the best sustainable option of its disposal. New EU regulations related to fertilizers derived from bio-waste and by-products assume the uniformity of legislation in Member States and simplification of procedures for introducing innovative fertilizers into the internal market.However, a direct application of sewage sludge to the soil is restricted by heavy metals content. Sewage sludge commonly includes pathogenic microorganisms and toxic compounds. The aim of the study was to determine the state of the art and availability of technology for fertilizers production based on waste, especially on sewage sludge. As sewage sludge from different wastewater treatment plants varies in its chemical composition and physical properties, it is important to find a local solution to the problem of sewage sludge disposal. It has been found that organo-mineral fertilizers (OMFs) derived from sewage sludge and modified by the addition of mineral fertilizers seem to be suitable for application to the soil. Adding acids or alkali agents provide sterilization and binding of the components. Novel OMFs gave a comparable crop yield response as conventional fertilizers. They show a slow release of nutrients, which is the main advantage in relation to mineral fertilizers.