The treatment of wastewater consumes large quantities of energy. Fortunately, inherent energy within the sludge produced from the process can be extracted as a methane-rich biogas using anaerobic digestion. Growing interest in energy efficiency and renewable energy production, along with increasing production of sewage sludge is leading water utilities to look at ways to optimize the anaerobic digestion process itself but also develop sludge pre-treatment technologies to produce additional energy and process more sludge.This session will present latest academic and water industry findings in this important area of research.
In the UK, approximately 75% of all sewage sludge produced is treated by anaerobic digestion (AD), with 3.6 million tonnes of treated biosolids recycled to agriculture, providing £25m nutrient value. In addition to sewage-derived biosolids, the non-sewage sludge AD sector has seen massive growth over the last decade. Across both sectors there are over 900 AD plants (in planning, construction, or operation), with only 161 treating sewage sludge. The environmental regulations in the UK for sewage and non-sewage sludge are relatively complex. There are currently a series of directives, Codes of Practice (CoP), Quality Protocols (QP), Publically Available Specifications (PAS), and assurance schemes covering the different aspects of sludge and biosolids management. Deregulation of the sludge market offers the opportunity to consolidate the regulations, and integrate the sewage sludge, non-sewage sludge, and other organic waste sectors. However, the route to a functioning market also has significant challenges, both economically and practically. The industry must overcome disparate regulation, emerging contaminants, and ultimately meet the needs of agriculture, for biosolids to be fully utilized as a resource. The UK model for biosolids recycling is not universal. In contrast, Switzerland has not used sewage sludge in agriculture since 2006.
Sludge thermal conversion, including pyrolysis and gasification has been a low adopted option for sludge treatment and disposal, particularly in Europe. Although there are clear advantages from the complete reduction and disinfection of sludge and production of waste heat, the low adoption of this solution has been due to the adverse environmental impact such as emission of hazardous substances (heavy metals) and due to the need for energy input. Discussions around different experiences, the impact of running conditions on emissions and observed environmental impact will be discussed as part of this sessions
As awareness of climate change and depletion of resources, including phosphorus, has increased in recent years, and as we move toward the realization of a low-carbon society, expectations about the use of carbon neutral biomass and resource recovery are mounting. Sewage sludge is one of these valuable resources and can be used as an energy source and a source for recovery of nutrients such as N and P. Advancements and different solutions for material and nutrient recovery will be shared, ranging on scales and effectiveness of processes. Innovations of the processes will be explored to inform on potential further developments in material recovery.
While developed countries are involved in the advanced concerns of sludge management, developing countries are at the stage of putting down their road map towards this end. Sludge management applications in developing countries are generally minimalist; typically limited to dewatering only which is followed by insecure disposal. The current approach may cause a threat to public and environmental health due to the presence of pathogens, heavy metals and other toxic chemicals in sludge. In bringing safe management practices to developing countries, exporting methods directly from developed countries is a commonly made unfortunate mistake. Solutions need to be developed by taking into account a number of local factors including social, financial and climatic. The destined end use of sludge should determine the processes that the sludge goes through. A legislative system addressing the local needs should complement the management system.
To address the need for small scale sludge treatment, a number of innovative developments or adaptations of larger scale sludge treatment have been developed and are being taken up, particularly for decentralised waste treatment (i.e. in remote areas) or for applications in emerging markets where centralised waste systems are not present or preferred. Examples include small scale dewatering solutions, anaerobic digestion reactor or small pyrolysis plants. Innovation on these solutions, experiences in the operation and maintenance of these solutions will be shared within this session.