Ammonia is one of the most persistent and problematic contaminants found in landfill leachate. Left untreated, it can pose a serious risk to receiving waters and make compliance with discharge consents difficult to achieve. Ammonia stripping – the process of physically removing ammonia from leachate using air – offers a proven, high-performance solution that can be tailored to a site’s available energy resources and treatment goals.
This article explains how ammonia stripping works, the two main process routes available, and the key design and performance parameters to consider when specifying a system.
Why Ammonia Removal Matters in Leachate Management
Landfill leachate typically contains elevated concentrations of ammoniacal nitrogen, generated as organic waste decomposes within the landfill body. Ammonia is toxic to aquatic life even at relatively low concentrations, and most environmental regulators – including the UK Environment Agency – impose strict discharge limits on ammonia in treated effluent.
Air stripping addresses this challenge directly by transferring ammonia from the liquid phase into a gas stream, where it can be captured, neutralised, or safely dispersed. It is a well-established technique in the water and wastewater industry, and when properly configured, can achieve very low residual ammonia concentrations even from highly loaded leachate streams.
Two Approaches to Ammonia Stripping
There are two established methods for stripping ammonia from landfill leachate, each suited to different site conditions and cost structures.
pH Driven Stripping
This method raises the leachate pH to approximately 12, typically by dosing lime or caustic soda. Raising the pH converts ammonium ions into free ammonia gas, which can then be stripped from the liquid using air in a packed bed column.
An added benefit of lime or caustic dosing is the precipitation of certain salts and larger organic molecules, which reduces residual Chemical Oxygen Demand (COD) alongside ammonia. A plate separator is commonly used downstream to remove the resulting suspended solids – these can be returned to the landfill site or passed forward to further treatment stages such as evaporation or reverse osmosis.
From the separator, leachate flows into a packed bed stripper column, where the partial pressure of ammonia in water is exploited to drive it out of solution. For very low residual ammonia targets, a multi-stage stripping process may be required. Exhaust air from the column can optionally be passed through an acid absorber to capture the stripped ammonia, and the treated leachate can be neutralised with acid before final discharge.
Large volumes of air per unit volume of leachate are required to achieve low effluent ammonia levels with pH driven stripping – this drives up operating costs, meaning the process tends to be more economically viable at lower flow rates.
Thermally Driven Stripping
The thermally driven route raises the leachate temperature to approximately 65°C to 70°C, using landfill gas or available waste heat, rather than adjusting pH with chemicals. This eliminates the need for ongoing chemical dosing, which can significantly reduce operational costs where a waste heat source is already available on site.
A thermally driven plant is more complex and carries a higher capital cost than a pH driven system. It typically includes:
- The stripping column itself
- An inlet heater
- A cooling tower for inlet air humidification
- A steam raising facility to fully saturate the stripping air
- Optionally, an exit air condenser to maximise overall plant efficiency
- Optionally, a thermal oxidiser to destroy stripped ammonia, or an ammonia gas scrubbing column to precipitate ammonia salts
Where waste heat is available, thermally driven stripping incurs substantially lower operational cost than pH driven stripping, since no chemical adjustment is needed. Where waste heat is not available, pH driven stripping is likely to be the lower-cost option – the right choice ultimately depends on local energy and chemical costs.
Choosing Between the Two Methods
Selecting the right process depends on site-specific factors, including:
- Availability of waste heat (e.g. from landfill gas engines, flares, or hot water/steam sources)
- Local energy and chemical costs
- Required flow rate and target residual ammonia concentration
- Available land area and capital budget
Organics has direct experience delivering both types of stripping system and can advise on plant and operational costs for a given site.
Technical Specifications
| Parameter | Detail |
|---|---|
| Flow rates available | 50 to 5,000 m³ per day |
| Residual ammonia (standard configuration) | As low as 10 mg/l |
| Materials of construction | Polyethylene and GRP (low temperature) up to stainless steel and high-grade alloys (elevated temperature / high corrosion potential) |
| Heat sources | Engine exhaust gases, flare exhaust gases, high-temperature hot-water streams, steam |
| Chemical requirements | Caustic soda/lime (pH adjustment); sulphuric/hydrochloric/phosphoric acid (pH re-adjustment); anti-foaming agent as needed |
| Energy requirement | ~450 MJ per m³ of leachate treated (≈25 m³ of landfill gas at 50% methane) |
| Waste heat example | A 1 MW electrical engine’s exhaust heat (~50% of electrical power) can treat 80–100 m³/day of leachate |
| Pre-treatment | Coarse filtration for solids over 2 mm diameter |
| Land requirement | A 200 m³/day stripper occupies approximately 120 m² |
Applications and Delivery Options
Ammonia stripping systems of this type are designed to scale across a wide range of landfill sizes, from small sites needing a modest 50 m³/day unit up to large regional facilities processing thousands of cubic metres daily. Delivery options include:
- Turnkey design, build and operate facilities for full end-to-end project delivery
- Pilot plant trials to validate performance and sizing before committing to a full-scale installation
- A range of instrumentation and control options to suit operational preferences and regulatory reporting needs
Key Takeaways
- Ammonia stripping removes ammonia from landfill leachate using either a pH driven or thermally driven process.
- pH driven systems raise leachate pH to ~12 using lime or caustic soda, and are typically more cost-effective at lower flow rates.
- Thermally driven systems heat leachate to 65-70°C using waste heat, avoiding chemical costs where a suitable heat source exists.
- Standard configurations can achieve residual ammonia concentrations as low as 10 mg/l.
- Systems scale from 50 to 5,000 m³/day and can be delivered as turnkey design, build and operate facilities, with pilot trials available for new installations.
Get in Touch
Choosing the right ammonia stripping approach depends heavily on the specifics of your site – available heat sources, leachate characteristics, discharge targets, and budget. Our technical sales team can help you evaluate pH driven versus thermally driven options, review pilot trial data, and design a system tailored to your landfill’s needs. Contact us today to discuss your leachate ammonia treatment requirements.