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Vertical (also known as Down Flow) reed beds, although not as numerous in the UK as horizontal flow beds at present, are being used increasingly in applications where horizontal flow beds would formerly have been specified.

The vertical flow (VF) systems are essentially the same as the horizontal flow systems in that they comprise a lined excavation. Unlike the horizontal flow reed bed the vertical flow is not constantly flooded but free draining. The effluent is applied in a batch process across the surface of the bed until the surface is flooded.

The effluent gradually drains down through the bed with air replacing the wastewater in the bed as it drains. The next dose traps the air which leads to a highly aerated system with good oxygen transfer permitting increased microbial growth and activity.

VF systems are more effective than HF systems at ammonia removal due to increased oxygen levels within them. VF systems have a smaller footprint than HF systems and can cope with stronger effluents.
To achieve a batch flow the effluent is delivered to the bed via a pump, flusher or siphon system. In preference we prefer to use the siphon systems as these require no power. The effluent is distributed over the bed sometimes aided by a layer of sand and then passes through the bed where treatment occurs. The effluent is collected in pipes positioned along the bottom of the bed and discharged through the outlet.
VF systems are less efficient at suspended solids removal and can be accompanied by a HF bed as part of a multi stage or hybrid system.