The currently applied paradigm for municipal wastewater treatment in the European Union does not meet basic sustainability criteria. Indeed, it runs counter to the stated goals of recent European Council policies regarding sustainable development.1 This disposal- based linear system uses aerobic microbiology as the core technology. This results – in the case of activated sludge plants, for example – in a requirement for large capital investment, heavy usage of fossil fuels, high- technology operational control and the generation of large quantities of sludge requiring treatment before safe reuse/recycle. Anaerobic digestion (AD) is a biological process of waste and wastewater treatment, which converts organic matter to biogas (a usable fuel) and a renewable energy source. The process occurs in bioreactors, where the microbes that carry out the process are retained as biofilms. Anaerobic digestion is an established, sustainable waste-treatment technology for residues from various sources, including industrial processes and agriculture. In addition to the generation of renewable energy, AD also has advantages over the conventional aerobic treatment approach, including lower capital and operating costs. To date, AD has not been applied for direct treatment of municipal wastewaters or domestic sewage in regions with a temperate climate, due mainly to concerns regarding the stability and efficiency of low-temperature AD. Recent advances in AD research and technology, however, have enabled high-rate, low- temperature anaerobic digestion (LTAD) as a feasible and potentially highly efficient approach. If proven feasible, an innovative municipal wastewater treatment approach, with AD as the core technology, could realise a major commercial and technological opportunity and facilitate future sustainable development in Ireland. This 36-month project evaluated, at laboratory scale and using state-of-the-art methodologies, the applicability and underlying microbiology of LTAD for municipal wastewater treatment under Irish conditions.