Resolis: Two 200m2 horizontal subsurface flow wetlands operated in paralell treating 10m3/d of secondary sewage.

Additional Info

  • In operation since: April 2007
  • Type of wastewater treated: Domestic
  • Type of wastewater (other): Secondary
  • Hydraulic load: 10 m³/day
  • Organic load (PE): 64
  • Organic design load (kg BOD/day): 3.8
  • Location: Resolis, The Black Isle, Scotland, UK
  • Client: Highland Council
  • Stage 1 type: Horizontal sub-surface flow
  • Stage 1 surface area (m²): 400
  • Cost: 55,000
  • Needs:

    The Highland Council constructed a school on the Black Isle near Cullicudden known as Resolis Primary School. Sewage effluent from the school was to pass through a septic tank and secondary treatment system prior to discharging back into the environment via a water course. The discharge consents for the secondary treatment element were not excessive and the council were keen to use as sustainable treatment solution as they could. The table below indicated the predicted flows and loads.





    Upper Tier  consents (mg/l)

    Lower Tier

    consents (mg/l)





    Suspended Solids








    Flow (m3/d)





    There was some land available towards the south of the school beyond the playing field where the septic tank was to be situated.

  • Solution:

    The discharge permit did not specify an ammonia consent and so a two horizontal subsurface flow wetland treatment system was selected as the most technically and economically effective solution at Resolis. The available land dictated that the beds should lie end to end but operate in parallel. A connection was made to the septic tank discharge and a splitter chamber was constructed to divide the flow from the septic tanks equally between the two reed beds. Each bed was 200 m2 totalling 400 m2. The reed bed was to also be an educational resource for the school highlighting the use of sustainable technologies. It was, however, important to provide fencing around the system due to the proximity of the playground to the treatment system. Access to the reed beds was only allowed under close adult supervision.

  • Benefits:

    The reed bed installation at the Resolis Primary School provided the local council with a sustainable, robust treatment solution for the new school and the children attending the school with awareness of the choices between standard and more sustainable technological solutions

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