A four-chamber baffled aeration tank can strip dissolved methane from leachate at up to 500 m³/day, and the same design can be scaled across several landfills by changing tank and pump sizes. A tender for four UK landfill sites used the existing leachate tank or lagoon as an inlet buffer, to cut civil work and smooth methane spikes.
The challenge: four sites, one specification
Each landfill had different leachate volumes, existing equipment and layouts. The target was to reduce methane from below 15 mg/l to below about 0.11 mg/l before discharge to sewer. Flows ranged from about 50 m³/day at the smallest site to 500 m³/day at the largest. The sites had an existing kiosk for the control panel, and one had a lagoon whose liner had lifted.
The approach
- Pump leachate from the existing storage tank.
- Filter it, meter it and dose diluted anti-foam.
- Pass it through a four-chamber baffled tank. Compressed air from the base of each chamber strips the methane.
- Collect it in a buffer tank with methane headspace monitoring, where samples can be taken.
- Discharge to sewer.
Control is by an Allen Bradley PLC with inverters on every motor and emergency stops. All pumps and compressors are also hard-wired so they can run manually.
Why use the existing tank as a buffer
The supplier gave three reasons in answer to the client’s questions:
- less civil construction, so less waste, carbon and installation time;
- standby mode in low flow, saving consumables, with start-up once a level is reached;
- dilution of methane peaks. Pumping direct from the field is prone to spikes and the plant would not run at its best.
Site by site
| Site type | Approach |
|---|---|
| Largest site (500 m³/day) | Existing tank as buffer, existing kiosk for panel |
| Smallest site (about 50 m³/day) | 5 m³ baffled tank and 5 m³ outlet tank, smaller pumps |
| Site with damaged lagoon | Repair the lagoon or replace it with a tank, after a site visit |
| Site with an existing stripper | Use the old plant as inlet buffer, add instruments and a bypass |
Answering the client’s questions
- Containment: a bunded concrete plinth with a sump, and pressure transmitters and flow meters to detect leaks.
- Odour: where tanks must be enclosed, an activated air unit using high-rate chemical oxidation can treat the vent.
- Telemetry: a 4G modem on the HMI can send alarms, at extra cost.
- Operator time: weekly anti-foam top-up (15 minutes), monthly carbon (1 to 2 hours, where used) and quarterly mechanical and electrical checks (half a day each).
Alarms shut the plant down safely, and restarting the next day causes no operational issues.
Running costs
The main items are electricity, with pumps of 10 to 30 kW and a 5.5 kW compressor, and anti-foam at about 150 litres a year at the largest site.
What to consider for your own project
- Reuse what exists where it is sound, and inspect it first.
- Size the buffer for methane dilution as well as flow.
- Ask about enclosure early. Air emissions guidance is moving toward odour and aerosol control.
- Plan operator time realistically.
See gov.uk landfill guidance for permitting. A smaller example is methane stripping at a small landfill.
FAQ
How is methane removed from leachate?
By bubbling air through it, which carries the dissolved gas out of the liquid.
Why four chambers?
Each has its own bubble mat, giving repeated contact between air and leachate.
What if the existing tank is damaged?
It may be repaired or replaced by a new tank.
Is the vent treated?
At low concentrations it was released to atmosphere, with enclosure and treatment as an option.
Planning leachate treatment?
Contact us with your leachate data.