Best Available Technology for P-Recycling from Sewage Sludge—An Overview of Sewage Sludge Composting in Austria

Abstract

In order to close the phosphorus cycle in the long term, efficient recycling processes are necessary to ensure that this critical nutrient can be returned to arable land. Sewage sludge recycling is of particular importance due to the relatively high phosphorus content of sewage sludge. In this article, the current recycling paths of Austrian sewage sludge are highlighted, focusing on the advantages and limitations of sewage sludge composting. In addition to nutrient contents, pollutant loads were also analyzed in order to also discuss the limitations of this recycling pathway. Therefore, data from Austrian composting plants with focus on sewage sludge are used. The results show that the currently relevant pollutants (heavy metals) are predominantly below the limits prescribed for recycling and spreading on arable land. However, in order to decide on a recycling path at an early stage, a pollutant monitoring system must be in place. Due to pollution, mono-incineration with subsequent phosphorus recovery is also currently being discussed in Austria. Mono-incineration can represent an important component of sewage sludge disposal, because some sewage sludges are not suitable for composting due to potential environmental hazards. Therefore, it is important that evidence-based limit values and measures for the reduction in pollutants for input sources are determined.

Composting of stabilized municipal sewage sludge with residues from agri-food processing in Poland

“…According to Gorlach and Mazur (2002), the phosphorus content of cattle manure is 0.28%, which makes the compost obtained in this study richer in phosphorus. Studies conducted by other authors have also shown that sewage sludge compost can be a good source of phosphorus (Stürmer & Waltner, 2021). In addition, the potassium content is also similar to that obtained in a study conducted by Bożym et al (2014), where it was 1.24% and 1.21% for one-and two-year compost, respectively.…”

“…However, to ensure the desired product quality, it is estimated that the share of sediment in the compost mass should not exceed approx. 30% by weight (Stürmer & Waltner, 2021). Therefore, composting sewage sludge is only possible with other substrates.…”