HYDRO1 consists of a sewage treatment system applied in decentralised areas with high seasonal loads.

The demo site will treat the domestic wastewater of Antissa village wastewater treatment plant (WWTP) located at the island of Lesvos, Greece. 

HYDRO1 combines anaerobic processes with constructed wetlands and disinfection to treat domestic wastewater as a completely circular solution where water, nutrias and the produced sludge are going to be reused. 

Furthermore, the anaerobic process recover energy in the form of biogas which will then be upgraded to produce high purity methane used to fuel local vehicles. 


Level of operation: Municipality – Community
Types of water treatment: Grey Water
By products: Fertilisers, Biogas, Reclaimed water for irrigation

HYDROUSA establishes the optimal operating conditions under which COD removal and biogas production are maximized.

The excess sludge from the UASB gets 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.

The first phase of HYDRO 1 construction started during the middle of July 2020 with the
excavations of the CWs and the establishment of the required concrete slabs (for the
installation of UASB, pilot CWs and biogas upgrade units).
Between August and October 2020, both saturated and unsaturated CWs (850 m 2 in total) were excavated and insulated with geotextile. After the installation of the influent pipes as well as the drainage and aeration pipe systems, the CWs beds were filled with the appropriate gravel and sand media and planted with 5 different reed species. During November 2020, most parts of the hydraulic and electrical piping system, the main manholes, the pumping station as well as the final effluent tanks were constructed. In December 2020, the UASB unit arrived at the Antissa plant in parts and the assembling was accomplished by AERIS and MINAVRA partners. During the same period, the pilot bio-electrified CWs, the aerated CW and the compact tertiary treatment unit were assembled in the HYDRO 1 site. The rest of HYDRO 1 major units (Composting system, Biogas upgrade unit, electromechanical equipment installation etc.) will be installed until the end of January 2021.


  • No wastewater discharge in the sea at dry weather
  •  Cheaper Production of reclaimed water
  • Increasing water supply
  • Recycling nutrients


  • 100 m³/d Nutrient rich water in Summer
  • 10 m³/d Nutrient rich water in Winter
  • <0.3 kWh/m³ of energy consumption
  • 10 MWh/year of biogas production
  • 10,000 m³/year of water reused in agriculture


m³/d raw sewage


m³/d of raw sewage