Slide 1
Hydro 1 Lesvos

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

The demo site treats 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 reused. Furthermore, the anaerobic process recovers energy in the form of biogas, which is then upgraded to produce high purity methane used to fuel local vehicles.

Slide 1
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Level of operation

Municipality – Community

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Types of water treatment

Municipal Wastewater

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By products

Compost, Biogas, Reclaimed water for fertigation

Read more about HYDRO1

HYDRO1 consists of a wastewater treatment train with a maximum capacity of 100 m3/d (anaerobic treatment stage followed by vertical flow constructed wetlands and post treatment units), a biogas upgrade system, a composting unit and four novel pilot scale constructed wetland systems.

The anaerobic treatment takes place in two UASB reactors, leading to the production of biogas and a small amount of sludge. The process recovers energy in the form of biogas, has low operating expenses and low footprint requirements. The biogas produced is collected in a gasometer and is being upgraded in order to produce pure biomethane which will be used as fuel, while the sludge is treated in a sequence of a sludge drying reed bed and a composting unit.

The anaerobic treated effluent is fed in the constructed wetlands, which serve as a secondary treatment providing further reduction of the organic carbon content and suspended solids of wastewater. The treated effluent from the wetlands is further fed to a post-treatment unit which consists of membrane filtration coupled to a UV disinfection system. Furthermore, four pilot-scale constructed wetlands are installed; one aerated CW and three bio-electrified wetlands. The treated effluent from the pilot scale units is further processed through a sand filter and a UV disinfection unit.

The full-scale CW system is designed with two stages: 1st stage, saturated downflow VF (VF1 SAT); 2nd stage unsaturated intermittent load VF CW (VF2 UNSAT). Different recirculation options allow us to test up to 6 different configurations, investigating the best scheme to meet the National and also other Mediterranean regulations (e.g., different water quality standards for nitrogen). HYDRO1 establishes the optimal operating conditions under which COD removal and biogas production are maximized.

Construction Phase

The first phase of HYDRO1 construction started during mid-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 m2 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 electroactive wetlands, the aerated CW and the compact tertiary treatment unit were assembled in the HYDRO1 site. Then, the biogas upgrade system was installed on site and tested.

At the end of May 2021, the construction works of the Sludge Drying Reed Bed (SDRB) and a biofilter for the treatment of compost system’s off gasses were completed, while the composting unit and a stainless steel biofilter were installed and connected to the SDRB system. Finally, all electromechanical equipment, automation systems and low cost and industrial sensors have been installed in the systems and HYDRO1 is fully operational from June 2021.

Operational Phase

The overall performance of the HYDRO1 is evaluated with a series of lab analyses and real time results from the online sensors.

Nowadays, the HYDRO1 is treating more than 67 m3 /d, achieving more than 95% of COD and TSS removal.

The performance of the CWs system treating the UASB effluent is consistently very high (average effluent COD is equal to 33 mg/L and BOD concentration is <10 mg/L), while complete nitrification and partial denitrification is also achieved. The lab analysis for the presence of pathogens in the final effluent of the unit revealed that no E. Coli bacteria are present, and the reclaimed water is appropriate for unrestricted irrigation.

In addition, micropollutants’ monitoring campaign has already started analyzing the water resulting from different treatment stages of the system and the final reclaimed water.


  • 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


100 m³/d raw sewage


10 m³/d of raw sewage