Technologies for waste treatment and conversion to energy have been around for more than 50 years. In particular, the most widespread and commercially viable process is anaerobic digestion of organic matter into biomethane, while gasification of biomass to hydrogen and syngas has also been commercialized in the last 10 years. However, these technologies and industries are almost always centralized and are of very large scales for the purpose of economies-of-scale. The scientific challenge and technological research is thus in modularizing and down-translating these processes, to enable them to be operated in a modular manner within a megacity such as Singapore and Shanghai. In addition to enabling a local material and mass cycle to be closed loop, it also minimizes the need for transportation of wastes to centralized facilities, which is one of the major energy consumption activities that has not always been accounted for. In our programme, we are studying a hybrid waste-to-energy system comprising a compact anaerobic digester and a biomass gasification system for converting municipal solid wastes to energy. A crucial issue that arises in sustainable megacities is that of the cycle of energy, water and waste. The key research question: How can we attain security and resilience in these areas given global uncertainties, resource limitations, and the high-density living environment?