Toward a Circular Economy of Sewage Sludge Anaerobic Digestion: Relevance of Pre-treatment Processes and Micropollutant Presence for Sustainable Management

Abstract

AbstractCircular economy is defined as a system in which the value of products, materials, and resources is maintained for as long as possible, minimizing their consumption and the generation of waste. Anaerobic digestion (AD) represents an attractive technology, as it uses waste to produce biogas as renewable energy and stabilizes the sewage sludge for land application. However, these potential benefits may be limited by negative impacts related to the land disposal of the stabilized sewage sludge due to the presence of organic micropollutants (OMPs) in the input sludge, and the inability of current AD methods to remove them is a recognized potential risk for human health and for the environment. However, as the conversion of sewage sludge during AD is limited by the low rate of hydrolysis of solids and complex organic compounds, the degradation of OMPs is also limited, as most pharmaceuticals, industrial additives, fragrances, and other synthetic compounds exhibit low biodegradability as a result of the high stability of most commercially available substances. While the effect of pre-treatments on the performance of anaerobic digestion has been studied mainly with the aim of increasing biogas production and reducing the volume of solids, the solubilization caused by pre-treatments can also increase the bioavailability of OMPs for anaerobic microorganisms, increasing its rate of degradation during the AD process.The selection of the most suitable sewage sludge management, in terms of their environmental sustainability, scenario for every particular scenario needs the usage of decision-making tools like life cycle assessment (LCA) that allow for the assessment of the potential environmental impacts of proposed strategies. The most relevant environmental aspects and impacts associated with sewage sludge generation and management could be found at the global, regional, and local level. The eutrophication, in terrestrial and aquatic ecosystems, or acidification is an environmental aspect at the regional level due to the sewage sludge disposal. However, human toxicity or infectious disease propagation and decreased quality of life could environmental aspects found at the local level.The aim of this chapter of this book is to show the circular economy of sewage sludge anaerobic digestion considering the relevance of pre-treatments and micropollutant presence for sustainability.KeywordsSewage sludgeAnaerobic digestionPre-treatmentOrganic micropollutantsCircular economyLife cycle assessment