Leachate treatment with an SBR (sequencing batch reactor) followed by a reed bed can treat landfill leachate on a small site at modest running cost, if the discharge consent is achievable and there is space and sun for the beds. A proposal for a 50 m³/day plant at a landfill in southern England shows how the two stages share the work, and how the design moved from a plain SBR to a natural finishing step.
The challenge: two small sites, strict surface-water targets
A waste company with two landfills wanted leachate treated to surface-water standards. Laboratory results for raw leachate set the objectives: reduce ammonia, chemical oxygen demand (COD) and suspended solids. The design flows were modest. At one site, 20 m³/day was currently dealt with by infiltration, with plans to size for 50 to 100 m³/day.
A meeting note recorded useful design cautions. A target COD of 50 mg/l might be impossible, because landfill leachate contains refractory COD, and COD is often not a discharge consent item anyway. The client also raised calcium carbonate fouling and the toxic limit for nitrogen in the biological stage.
The approach: SBR first
The first proposal was a single SBR with a wetted volume of about 400 m³, 5 m high and 10 m in diameter, in glass-lined steel on a concrete base. It would reduce suspended solids, COD and some ammonia, producing two outputs: sludge from the base and treated leachate.
- UPVC pipework suitable for leachate.
- Duplex inlet filters taking out solids above 3 mm.
- One skid with pumps and motors for circulation and aeration.
- PLC control with float switches for level.
- Options: a roof with odour control, gravity sludge thickening, flow meters and online analysers.
The performance target was an exit COD below 100 mg/l, ammonia below 2 mg/l and suspended solids below 25 mg/l, from an inlet COD of 3,600 mg/l and ammonia of 500 mg/l.
Adding a reed bed
For the second site, a later revision chose a natural route. The SBR kept its venturi aerators, which stir and aerate at once, a filtration package and a floating decanter. A reed bed polishes the SBR effluent.
- Area calculated at 320 m² for 50 m³/day.
- Two beds in parallel, each 6.4 m by 25 m.
- Flood-and-drain on a three-day cycle while the reeds develop, then continuous flow split between the beds.
- About three full growing seasons to reach mature conditions.
- The site must not be shaded by trees or buildings at any time of day or year.
The price was a budget figure only. A survey would settle whether a liner is needed and whether levels allow gravity flow from SBR to discharge.
Why it works, and its limits
The SBR does the heavy biological work in batches. The reed bed then removes residual nutrients and solids with no power and little attention. The cost of that simplicity is time and space. Reed beds need years to mature, and an earlier note from another leachate enquiry put their ammonia removal at about 40%, not enough on their own for a tight consent. Here the SBR carries the ammonia load.
Commissioning is seasonal too. Process commissioning took four to six weeks, depending on the time of year, because bacteria are more active in summer, and on leachate availability.
What to consider for your own project
- Get firm consent figures before choosing a process.
- Do not over-specify COD. Refractory COD may make low targets unreachable.
- Allow time for reeds. Plan on three growing seasons.
- Protect the bed from shade and check levels for gravity flow.
- Decide where sludge goes: back to the site, thickened, or tankered.
The Environment Agency’s landfill permit guidance sets out discharge requirements for UK sites.
FAQ
What is an SBR?
A sequencing batch reactor treats leachate in timed batches: fill, aerate, settle and decant, all in one tank.
Can a reed bed remove ammonia?
Only partly. A figure of around 40% was quoted in other correspondence, so a biological stage should carry the main load.
How long does a reed bed take to establish?
About three full growing seasons in this design.
Why are commissioning times quoted as ranges?
Biological activity depends on the season and on how much leachate is available.
Treating leachate on a small site?
Contact our engineers with your leachate results and consent.