Abstract
The fertilizer framework in the European Union has recently been reviewed by EU Regulation 1009/2019 that excluded sewage sludge from the list of the possible constituents of organic fertilizers relying on their origin, not on their quality. This paper aimed to carry out a complete characterization of sewage sludge obtained from a pharmaceutical manufacturing process (PDSS) to demonstrate that sewage sludge obtained from a standardized and controlled manufacturing process can be safely recycled as organic fertilizer. The agronomic and environmental characteristics of the PDSS product were analyzed and compared to other organic fertilizers. Its fertilizing potential was also evaluated through plant growth trials. PDSS was characterized by a high concentration of total N (6.6% w/w), which was all present in organic form. PDSS also showed a low concentration of heavy metals, an absence of pathogens and low concentrations of organic contaminants. Plant growth trials showed that the PDSS was able to improve lettuce and carrot growth (+25 and +46% of dry weight compared to the unfertilized control), as well as their physiological status. Considering all the results, the exclusion of sewage sludge relying only on its origin and not on its quality appears to conflict with the principles of the circular bioeconomy.
Highlights
The world’s population continues to grow, with a medium-variant projection indicating that the global population could reach 10 billion in 2050 [1]
The sub-alkaline pH is typical of sewage sludge, mature compost and manures, and it was related to the presence of basic cations (Ca and Na)
The sludge showed a high concentration of Total organic C (TOC) and total N (35.5 and 6.6% w/w), with the N represented by only organic N
Summary
The world’s population continues to grow, with a medium-variant projection indicating that the global population could reach 10 billion in 2050 [1]. The need for more food production is evident to feed the world’s growing population, as well as to achieve the Sustainable Development Goals, i.e., Zero Hunger, defined by the United. Agricultural productivity has been enhanced mainly by using fertilizers, and world demand for nitrogen, phosphorus and potassium for fertilizer use is expected to increase by about 10% from 2016 to 2022 [4]. The increasing requirement for fertilizers poses serious issues related mainly to their production and environmental impact. Synthetic N and P fertilizers are commonly produced from non-renewable resources using high-cost processes [5,6], and environmental issues related to their use are well known (e.g., eutrophication, gaseous emissions) [7]. The use of organic fertilizers has enhanced the sustainability of agricultural production, decreasing the need for non-renewable resources and the environmental impact of agriculture [8]. It was recently reported that anaerobic digestate can replace urea as a fertilizer in agriculture without increasing ammonia emissions and reduces the risk of soil and water pollution [9,10]
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