Conversion of Sewage Sludge and Other Biodegradable Waste into High-Value Soil Amendment within a Circular Bioeconomy Perspective

Resource recovery from biodegradable waste is essential in order to reach the goals of zero circular economy waste generation and zero greenhouse gas emissions from the waste sector. Waste whose management is a real challenge is sewage sludge, mainly because of high concentrations of heavy metals. The aim of this study was to compare the effectiveness of material stabilization during aerobic stabilization of two feedstocks with sewage sludge obtained from different sources, namely, digestate from a municipal wastewater treatment plant and digestate from a co-digestion process. Moreover, the goal of the experiment was to assess the quality of compost in terms of remediation potential. The composting process was carried out for four different mixtures consisting of the mentioned digestates, municipal solid waste, and grass. A better composting efficiency with digestate from the co-digestion process was observed. In that case, a higher temperature in the thermophilic phase (> 55 degrees C) and a higher organic matter loss ratio (60%) were obtained as compared to the process with digestate from wastewater treatment plant. Taking into account the fertilizing properties and the concentration of heavy metals, all obtained composts met the requirements set out in the Polish Regulation for organic fertilizers. Only the content of Helminth eggs in the composts produced with the digestate from the wastewater treatment plant was above the acceptable level. The research also proved that the produced composts can be used in the phytoremediation process of the degraded area. It was found that all composts caused a significant increase in fescue biomass. The highest yield was achieved for compost produced from a mixture with the addition of 30% sewage sludge from the co-digestion process.

Automated summary

The study aimed to compare the effectiveness of different digestates in the aerobic stabilization process and evaluate the quality of compost. It was found that digestate from the co-digestion process had higher composting efficiency with higher temperature and organic matter loss ratio. All composts met the requirements for organic fertilizers except for Helminth eggs content in compost produced from digestate from the wastewater treatment plant. The research also demonstrated that the produced composts can be utilized in the phytoremediation process for degraded areas, with significant increase in fescue biomass observed.