Abstract
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. The characteristic of organo-mineral fertilizers obtained from dried sewage sludge is presented in the paper. In order to obtain balanced NPK fertilizers straight mineral fertilizers, poultry litter ash and phosphoric/nitric acids or a mixture of these were added. As a result organo-mineral fertilizers with N + P2O5 + K2O > 20% were produced. It was found that the largest contribution of contaminants in products comes from Wet Process Phosphoric Acid.
Highlights
A lot of attention has been recently paid to sewage sludge disposal due to its increasing amount and tightened legislation in the European Union (EU) referring to its final disposal methods
The composition of the obtained organo-mineral fertilizers is presented in Fig. 1. 30–41% by weight of dried sewage sludge was used in order to limit introducing heavy metals to the product
To produce Organo-mineral fertilizers (OMFs) I, OMF II and OMF III potassium chloride was used, in samples (IV–VIII) it was replaced by poultry litter ash to avoid introducing chloride ions which are undesirable in fertilizers
Summary
A lot of attention has been recently paid to sewage sludge disposal due to its increasing amount and tightened legislation in the EU referring to its final disposal methods. It is estimated that in the year 2020 approximately 13 m tonnes of sewage sludge will be generated in EU27 [1]. In last years a tendency for thermal methods of sewage sludge disposal has increased [7, 8]. Despite the advantages of thermal methods including significant reduction in volume as well as phosphorus and energy recovery, one fact should be taken into account: this disposal method is not in line with Circular Economy concerning cutting of C O2 emissions and nutrient recycling (especially organic compounds and nitrogen) [9]. It is important with reference to phosphorus which is limited [11, 12]
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