Leachate disposal is one of the most persistent operational challenges facing landfill operators. It is costly to haul away, difficult to treat on-site to discharge standards, and its volume rarely shrinks on its own. Where waste heat is already available — whether from landfill gas combustion or from waste heat recovery on power generation equipment — leachate evaporation offers a genuinely attractive alternative to conventional disposal routes.
By vaporising the water content of leachate, evaporation systems concentrate the dissolved and suspended solids into a much smaller volume, drastically cutting the amount of material that ultimately needs to be transported or disposed of separately.
What Is Leachate Evaporation?
Leachate evaporation systems boil off moisture from landfill leachate (or similarly composed waste waters), leaving behind a concentrated residue for separate handling — typically via drying or filter-pressing. The vapour produced can be condensed for additional thermal efficiency or, in open-loop configurations, disposed of via an enclosed flare.
Systems are engineered to operate either:
- Above 100°C, using pressurised steam or hot water, or
- Below 100°C, using a vacuum to lower the boiling point where only lower-grade waste heat is available.
This flexibility means the technology can be matched to whatever heat source a site actually has, rather than requiring a premium fuel supply purely to run the evaporator.
At a glance: Systems handle flows from 10 to 2,000 cubic metres per day, with multi-stage configurations available for maximum concentration of the residual solids.
How the System Works
Multi-Stage Design
Cost-effective operation is usually achieved using two to four evaporator stages. Each stage is built identically and includes:
- A circulation pump
- A fluidised bed heat exchanger
- An evaporator vessel
The fluidised bed heat exchanger is a key design feature — it prevents scale and solids deposits from building up on heat exchanger surfaces, which would otherwise degrade performance over time.
Steam and concentrate flow in parallel through each stage, moving along the pressure gradient towards a vacuum pump positioned downstream of the final stage. The first stage can be heated directly with primary steam from a steam generator, or, in deep vacuum systems, with waste heat in the form of hot water. Every subsequent stage is then heated using the waste vapours carried over from the stage before it — a cascading design that squeezes maximum value from the available heat.
If the electrical conductivity of the final concentrate becomes too high, condensate can be automatically recycled back to the circulating evaporator’s receiver vessel, helping maintain stable operation.
Dewatering proceeds continuously from stage to stage, with the final concentrate drawn off for drying or filter-pressing.
Managing Solids Build-Up
Solids build-up on heat exchanger surfaces is one of the hardest variables to predict at the design stage. Deposits result not just from normal fouling but are compounded by scaling from dissolved solids in the leachate — and since every site’s leachate composition differs, systems must be designed against a worst-case scenario informed by experience with similar leachate types.
Heat Transfer Mechanisms
Evaporators (sometimes called “reboilers” in process engineering terms) rely on one of five heat transfer mechanisms:
- Single-phase liquid convection
- Liquid falling-film evaporation
- Nucleate (pool) boiling
- Two-phase convective boiling with sub-cooled or saturated liquid
- Dry wall convection
Falling-film evaporation, pool boiling, and two-phase convection all deliver significantly better heat transfer coefficients than single-phase or dry wall convection — dry wall convection is so inefficient it is rarely used in practice. The right choice depends on solids concentration range, the grade of waste heat available, disposal options for both vapour and concentrate, applicable environmental regulations, and customer preference.
Key Features Summary
- Leachate volume reduction driven by waste heat
- Pressure and vacuum system options, depending on waste heat grade
- Open-loop and closed-loop configurations
- Closed-loop condensation for improved thermal efficiency
- Open-loop disposal to enclosed flare
- Multi-stage systems for maximum concentration
- Flow range from 10 to 2,000 m³/day
- Material grades selected specifically for duty
- Optional on-line monitoring, with internet connection and data logging
Technical Specifications
| Parameter | Value |
|---|---|
| Flow rate range | 10 – 2,000 m³/day |
| Energy requirement | ~2,000 MJ per m³ of leachate evaporated |
| Equivalent landfill gas (50% methane) | ~120 m³ per m³ of leachate |
| Waste heat from 1 MW engine-generator | Evaporates 20–25 m³/day of leachate |
| Pre-treatment requirement | Coarse filtration, solids >2 mm removed |
| Chemical dosing | Anti-foaming agents (process-dependent) |
| Land requirement (20 m³/day unit) | ~25 m² |
| Materials | Explosion-clad materials for high-quality, cost-effective surfaces |
A single 1 MW engine-generator, using roughly 50% of its exhaust heat, can supply enough waste heat to evaporate 20–25 cubic metres of leachate per day — turning what would otherwise be wasted thermal energy into a practical treatment solution.
Economisers: Extending Waste Heat Recovery
Beyond forced-feed reboilers for leachate evaporation, the same engineering approach extends to economisers for recovering heat from hot source gases — operating at temperatures approaching 800°C. These units can recover heat from engine exhausts, flare exhausts, and other high-temperature process off-gases, making them a useful complementary technology wherever waste heat streams exist on-site.
Design, Build, and Quality Standards
All reboiler and condenser heat transfer equipment is designed in-house and built to the recommendations of TEMA (the Tubular Exchanger Manufacturers Association), with all calculations subject to rigorous checking procedures. Manufacturing is carried out under Lloyd’s Register third-party inspection systems, with other inspection bodies accommodated where preferred.
Choosing the Right Process Route
Selecting the optimum evaporation process for a given site requires a structured assessment of several factors:
- Leachate flow rate
- Leachate composition
- Waste heat availability and type
- Options for concentrate disposal
- Site-specific restrictions — emission limits, site licence conditions, etc.
This information establishes the principal process options, which are then refined against technical resources, land availability, management infrastructure, and the required degree of automation. Final selection is based on a comparison of capital and operating costs.
Typical Applications and Track Record
Leachate evaporation technology has been applied across systems ranging from 200 to 1,800 cubic metres per day, with designs including forced-feed evaporators, kettle reboilers, saturated air-stream condensers for energy recovery, economisers for waste heat recovery, and humidifier evaporators.
Key Takeaways
- Leachate evaporation converts available waste heat — from landfill gas or power generation exhaust — into a practical, volume-reducing leachate treatment method.
- Multi-stage evaporator designs with fluidised bed heat exchangers manage solids build-up and cascade heat efficiently between stages.
- Systems scale from small 10 m³/day installations to large 2,000 m³/day plants, with material and process selection tailored to each site’s leachate characteristics.
- Complementary economiser technology can extend waste heat recovery to other high-temperature gas streams on-site.
If your site has waste heat going unused and leachate disposal costs climbing, it’s worth exploring whether an evaporation system could turn that liability into a manageable, on-site process. Get in touch with our Technical Sales Department to discuss a leachate assessment tailored to your site’s flow rates, composition, and available heat sources.