Ammonia stripping removes ammonia from landfill leachate by heating it and passing air through it, and for strong leachate the sensible aim is often bulk reduction rather than a polished effluent. A quotation for a 300 m³/day plant at a sewage works took leachate at up to about 7,000 mg/l down to roughly 1,750 mg/l, a reduction of 75%. This post explains that design and the choices behind it.
The challenge: very strong leachate
Ammonia in leachate is toxic to aquatic life and is usually the hardest parameter to meet at discharge. At 7,000 mg/l it is far beyond what a biological plant can accept directly. The client wanted a plant that would cut the load heavily, in a robust form that would not need much operator attention.
The approach: one skid, two columns
The design conditions were an inlet flow of 300 m³/day, an inlet concentration up to 7,000 mg/l, and an outlet of about 1,750 mg/l. The main elements were:
- A dual stripper and cooling column using packing-free vortex scrubber technology. No packing means no packing to clean.
- Combined functions in one tower: stripping, cooling of the outgoing liquid and pre-heating of incoming air.
- Dual-path feed filtration, each filter able to take the full flow, with gauges to show pressure drop.
- A stripping air blower of 6,000 Nm³/h, direct-drive to avoid belt failures, with a variable-speed controller to tune airflow and so outlet ammonia.
- A steam-fed feed heater. The process works by thermal conversion of ammonium ions to ammonia gas, using steam already available on site.
- An acid absorber option. The exhaust can be bubbled through sulphuric acid to capture the ammonia as ammonium sulphate.
No chemical additions are needed, apart possibly from an anti-foam agent whose need depends on the organics in the leachate. The unit was designed to be mobile, although with two columns it needs some dismantling for transport.
Why bulk reduction
The plant is not designed for very low concentrations. Getting from 1,750 mg/l to a few mg/l needs extra stages, and the supplier noted that minor modification and more sections could do this. A bulk-reduction plant is cheaper and simpler, and the remaining ammonia can go to a sewage works or a second treatment step.
Other variants in the same period show the range. A small mobile 25 m³/day unit took ammonia from 60 mg/l to below 10 mg/l, using an 8 m packed column, acid and caustic dosing and a diesel generator for remote use. A study for a large wastewater flow used five 20 m columns for 200 mg/l down to 5 mg/l. The packing-based designs have a drawback the supplier flagged: solids can deposit on the packing and raise pressure drop, and how fast depends on the wastewater.
What the quote left to the client
Civil works, steam raising, the electrical supply, water for steam and boiler treatment, signal cabling and sludge handling were excluded. These are significant items, so check them in any comparison.
What to consider for your own project
- Decide the target. Bulk reduction and a final consent are different jobs.
- Find a heat source. Steam or waste heat makes stripping economic.
- Think about the exhaust. Ammonia in the air can be absorbed in acid to make a saleable salt.
- Plan for fouling. Scale and solids affect packed columns more than packing-free ones.
- Check foaming with a sample of your leachate.
Discharge limits for leachate are set in your permit. See the Environment Agency’s landfill operator guidance.
FAQ
How does ammonia stripping work?
Heated leachate releases ammonia as a gas, which is carried away by an air stream passing through the column.
What happens to the stripped ammonia?
It can be absorbed in sulphuric acid to form ammonium sulphate, or sent to a thermal oxidiser.
Do I need chemicals?
Not in this design, apart from possible anti-foam. Some other designs dose acid and caustic to adjust pH.
Can a stripper reach very low ammonia levels?
With more stages, yes. This design aimed at bulk reduction only.
Treating strong leachate?
Send us your leachate analysis and we will outline a stripping option.