HYDRO1 consists of a sewage treatment system to be applied in decentralised areas with high seasonal loads. In HYDRO1, the UASB technology will operate even at relatively low temperatures, taking advantage of the much lower flows of sewage in winter, which allow to increase the hydraulic retention time (HRT). HYDROUSA establishes the optimal operating conditions under which COD removal and biogas production are maximized. The excess sludge from the UASB will be mixed with biomass and co-composted in an innovative in-vessel composting system, with humidity capture and plants that treat the odours. According to legal constraints the UASB effluent will either be treated in constructed wetlands (CWs), filtered and disinfected for reuse in agriculture, or will directly be used for fertigation after disinfection. The produced biogas will be upgraded to methane to be valorised as a fuel. Specifically, three CW systems will be established in parallel: (1) a full-scale CW (100 m3/d), (2) a pilot scale bio-electrification CW system (1 m3/d) and (3) an aerated CW (1 m3/d). (2) and (3) are defined as “enhanced CWs” and will be used to reach treatment needs in summer when wastewater generation increases. The UASB-CW effluent will be filtered and treated with UV to satisfy the needs of the wastewater legislation in place.