Orhei municipality - Moldova

The Orhei Constructed Wetland treatment plant, the biggest secondary treatment entirely based on CWs in the world

The city of Orhei was equipped with an old wastewater treatment plant, a high rate percolating filter, no longer sufficiently effective for the treatment itself of the whole city and the future scenarious. For this reason the Moldovian government, under a World Bank programme and relative feasibility study, decided to replace it with a constructed wetland system at the service of about 26000 inhabitants and few agro-industries.

The Orhei CWTP consists of usual pre-treatment and an equalization with pre-aeration; the primary sedimentation phase has been skipped, because it's carried out directly at the secondary treatment stage by the so-called French system. The system consists of 4 lines operating in parallel independently, each composed of two VF stages in series. Total gross area is about 5 ha. Surely one the largest Constructed Wetlands for secondary treatment of municipal wastewater present worldwide!

Design Team: SWS Srl, IRIDRA Srl, HYDEA Srl, POSH&Partners GmbH

Realisation Works by: HEILIT Umwelttechnik GmbH in association with BioPlanta GmbH

Additional Info

  • In operation since: 2013
  • Type of wastewater treated: Domestic
  • Type of wastewater (other): + food processing
  • Hydraulic load: 4600 m³/day
  • Organic load (PE): 21.666 PE
  • Organic design load (kg BOD/day): 1300
  • Location: Orhei
  • Client: PIU Moldovia - WorldBank
  • Stage 1 type: French system
  • Stage 1 surface area (m²): 18.000
  • Stage 2 type: Vertical flow, unsaturated
  • Stage 2 surface area (m²): 17.000
  • Cost: 3.387.000 €
  • Needs:

    The primary need is to substitute the old wastewater treatment plant, a high rate percolating filter, very expensive especially for its localisation on top of the hill where the city wastewater ha to be pumped up, and no longer sufficiently effective for the treatment itself of the whole city.

  • Solution:

    The Moldovian government, under a World Bank programme and relative feasibility study, decided to replace it with a constructed wetland system at the service of about 26000 inhabitants (2022 prevision), and few food processing industries. During the peak period of food processing industries, the CW system will capable to treat a maximum organic load of 2000 KgBOD/day (more than 33.000 P.E., 2022 prevision). At its start the average load is 700 KgBOD/day (11.666 PE) with a peak of 1200 KgBOD/day (20.000 PE).
     
    The Orhei CWTP consists of screening, grit removal and equalization with pre-aeration system as a primary treatment; the primary sedimentation phase has been skipped, because it's carried out directly at the secondary treatment stage by the so-called French system. The system consists of 4 lines operating in parallel independently. Each line is composed of two stages in series:1st Stage - French system (vertical flow reed beds fed with raw wastewater where there's a formation of a sludge aerobic layer on the surface, removed every 10-12 years.2nd stage - vertical submerged flow reed beds.Total surface is about 35.000 m2 (3,5 ha) and the gross area is about 5 ha. Surely one the largest Constructed Wetlands for secondary treatment of municipal wastewater present worldwide!
     

  • Benefits:

    Development countries often need of low technology treatment system to contain operational costs and to achieve high efficiency without the need of very qualified and specialized personnel. The designed system is characterized by low energy consumption and very low production of surplus material, considering that the sludge extraction will happen after many year and that the sludge should be reused in agricolture as soil conditioner. The flexibility of CWs, and especially of the French scheme, permits to control the impacts not only of Orhei inhabitants, but also of the agro-food industries of the area, currently without any pre-treatment and characterized by a seasonal production of wastewater with high organic content.

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