How Can DTRO Concentrate from Landfill Leachate Be Effectively Treated?

22 Sep, 2026 2:06pm

Landfill leachate treatment often relies on DTRO (Disc Tube Reverse Osmosis) as one of the main advanced treatment technologies. However, many landfill operators face a difficult question after the DTRO system starts working: What should be done with the 20%–30% concentrate generated by the membrane system?

This concentrate contains high levels of salts, COD, hardness, and other pollutants. Direct discharge is generally not an option. Returning it to the landfill can cause salts and contaminants to accumulate continuously, making the leachate increasingly difficult to treat. For many landfill projects, DTRO concentrate therefore becomes the last and most difficult part of the treatment process.

This article looks at the characteristics of DTRO concentrate, compares common treatment methods, and explains why evaporation and crystallization can provide a more complete treatment route.

1. DTRO Concentrate: A Difficult By-Product to Handle

Landfill leachate treatment commonly uses membrane processes such as NF, RO, and DTRO after biological treatment. With its open-channel design and strong resistance to fouling, DTRO is well suited to leachate with high turbidity, high SDI, high salinity, and high COD.

However, membrane separation is essentially a physical separation process. Clean water passes through the membrane, while salts and other pollutants are retained. The result is a concentrated liquid stream.

DTRO concentrate can account for approximately 20%–30% of the original leachate flow. For example, a landfill treating 500 tons of leachate per day may generate around 100–150 tons of DTRO concentrate every day.

Typical characteristics include:

Characteristic	Description
High COD	COD can typically reach 8,000–30,000 mg/L, while biodegradability is poor and the BOD/COD ratio is often below 0.1.
High salinity	Conductivity can reach 50,000–150,000 μS/cm, with high concentrations of chlorides, sulfates, and other inorganic salts.
High hardness	Calcium and magnesium concentrations can reach 2,000–8,000 mg/L as CaCO₃, creating a significant scaling risk.
Variable pH	pH is commonly around 6.0–8.0, although lower values may occur at certain stages of treatment.
Low flow volume	The concentrate volume is already significantly lower than the original leachate volume.
Low biodegradability	With BOD/COD below 0.1, biological treatment becomes increasingly difficult.

Without an effective treatment route, operators generally face two choices: send the concentrate off-site at a high cost or return it to the landfill and risk the gradual accumulation of salts and pollutants.

Neither option addresses the underlying problem.

2. Comparing Common DTRO Concentrate Treatment Methods

Several approaches have been used to manage DTRO concentrate. Each has its own limitations.

Treatment Method	Basic Principle	Main Limitation
Landfill Recirculation	Return the concentrate to the landfill for further absorption and treatment.	Salts and pollutants continue to accumulate, increasing the treatment burden on the overall leachate system.
Off-Site Disposal	Transport the concentrate to a qualified third-party treatment facility.	High disposal and transportation costs, limited receiving capacity, and potential transportation risks.
Advanced Oxidation	Use highly reactive species to oxidize organic pollutants.	High salinity can reduce treatment efficiency, while chemical consumption can make the process expensive.
Spray into Incinerator	Introduce the concentrate into an incinerator for high-temperature treatment.	Capacity depends on available furnace load and may affect combustion conditions, flue gas performance, and equipment corrosion.
Evaporation and Crystallization	Separate water from salts and pollutants through phase change and crystallization.	Higher initial investment, but provides significant volume reduction and a more complete final disposal route.

From an engineering perspective, recirculation and off-site disposal mainly transfer or postpone the problem. Advanced oxidation can reduce organic pollutants but does not fundamentally separate the high salt load. Evaporation and crystallization takes a different approach by separating water from concentrated salts and pollutants and converting the remaining liquid into a much smaller volume of solid residue.

3. Evaporation: Why Is It Considered a Final Treatment Route?

3.1 The Principle of Evaporation and Crystallization

The basic principle of evaporation is phase separation.

Heat is applied to the concentrate so that water evaporates, while salts and non-volatile pollutants remain in the concentrated liquid. As the concentration increases and the solution reaches supersaturation, salts can precipitate and form crystals.

A mechanical vapor recompression (MVR) evaporator can continuously concentrate DTRO concentrate until crystallization conditions are reached.

The key advantage is that pollutants are no longer retained entirely in the liquid phase. Instead, water is separated as vapor and subsequently recovered as condensate, while salts and other concentrated pollutants are transferred into a solid or highly concentrated residue. This significantly reduces the volume of liquid requiring final disposal.

3.2 MVR vs. Conventional Multiple-Effect Evaporation

Traditional multiple-effect evaporation relies mainly on external steam as the heat source. Steam passes through multiple evaporation stages, with heat being reused from one effect to the next.

MVR takes a different approach. The secondary vapor generated during evaporation is compressed to increase its temperature and pressure, then reused as the heating source.

As a result, MVR can significantly reduce the need for fresh steam.

Comparison	Traditional Three-Effect Evaporation	MVR Evaporation
Energy source	Fresh steam	Electricity
Typical energy consumption	About 0.45–0.60 tons of steam/ton of water	About 38–55 kWh/ton of water
Indicative operating cost	About RMB 90–120/ton of water	About RMB 23–33/ton of water
Heat utilization	Heat is reused between effects	Secondary vapor is continuously recompressed and reused

The actual energy consumption and operating cost depend on feedwater quality, evaporation temperature, equipment configuration, energy prices, and operating conditions. For a landfill generating around 100 tons of DTRO concentrate per day, MVR evaporation can potentially reduce long-term disposal costs compared with continuous off-site treatment. The actual payback period should be calculated based on the project's concentrate characteristics, energy prices, disposal costs, and equipment investment.

4. WTEYA's Recommended DTRO Concentrate Treatment Process

Based on the characteristics of landfill leachate concentrate and practical engineering requirements, WTEYA recommends the following treatment route:

DTRO Concentrate → Pretreatment & Softening → MVR Evaporation → Mother Liquor Drying → Condensate Polishing → Discharge or Reuse

4.1 Step 1: Pretreatment and Softening

Pretreatment is critical for stable evaporator operation.

DTRO concentrate often contains high levels of calcium and magnesium. If these hardness ions enter the evaporator without sufficient pretreatment, they can form scale on heat-transfer surfaces.

Scaling reduces heat-transfer efficiency, increases energy consumption, and can eventually affect continuous operation.

A typical softening process uses chemicals such as sodium hydroxide and sodium carbonate to precipitate calcium and magnesium as CaCO₃ and Mg(OH)₂. The resulting solids can then be removed through clarification or suitable filtration.

Typical control targets may include:

Total hardness: below 100 mg/L
Calcium: below 20 mg/L
Magnesium: below 10 mg/L

The actual targets should be determined through water analysis and pilot testing.

4.2 Step 2: MVR Evaporation and Concentration

After pretreatment, the concentrate enters the MVR evaporation system.

Under forced circulation and vacuum conditions, the liquid is heated and partially evaporated. Water vapor is separated and condensed, while salts and non-volatile pollutants remain in the concentrate.

Typical operating parameters may include:

Evaporation temperature: approximately 75–85°C
Absolute pressure: approximately 30–50 kPa
Concentration: adjusted according to salinity, scaling characteristics, and target crystallization conditions
Volume reduction: the concentrate can potentially be reduced to approximately 5%–10% of its original volume

Forced circulation helps maintain a high flow velocity through the heat-transfer system, reducing the risk of localized scaling.

4.3 Step 3: Mother Liquor Drying

As evaporation continues, salts and organic pollutants become increasingly concentrated. Not all components will crystallize under the same conditions. High levels of organic matter can remain in the mother liquor even after significant salt crystallization has occurred.

The remaining mother liquor therefore requires further treatment, such as mother liquor drying, to achieve the required final reduction and avoid returning the concentrated liquid to the landfill. This step is important when the project aims for a more complete liquid-free treatment process.

4.4 Step 4: Condensate Treatment and Reuse

The water vapor generated during evaporation is condensed into condensate.

Although the condensate is significantly cleaner than the original DTRO concentrate, trace organic compounds and other contaminants may still carry over with the vapor. A condensate polishing system can therefore be used to further improve water quality.

Depending on the project requirements, the treated condensate can be discharged according to the applicable standard or reused within the facility.

Indicative targets may include:

Conductivity: <100 μS/cm
COD: <30 mg/L
Ammonia nitrogen: <10 mg/L

Actual condensate quality depends on feedwater composition, evaporator operation, vapor separation, and the downstream polishing process.

5. Comprehensive Benefits of the WTEYA System

A properly designed DTRO concentrate treatment system can achieve significant liquid volume reduction while recovering a large portion of the water as condensate.

Typical project indicators may include:

Indicator	Typical Value
Concentrate reduction rate	≥95%
Condensate recovery rate	≥90%
Salt sludge moisture content	<20%
MVR evaporation power consumption	38–55 kWh/ton of water
Final residue	Concentrated salt/sludge residue

Actual performance varies according to feedwater characteristics, process configuration, operating conditions, and project requirements.

Key Advantages

Significant volume reduction: The liquid volume can be reduced by more than 95% under suitable operating conditions, greatly reducing the burden of final disposal.

Controlled energy consumption: MVR recovers secondary vapor as a heat source, reducing dependence on fresh steam.

Water recovery: Treated condensate can potentially be reused or discharged after meeting the required water-quality standards.

Reduced liquid waste: Salts and concentrated pollutants are separated from the liquid phase and transferred into a much smaller solid or concentrated residue stream.

Integrated operation: A properly designed system can integrate pretreatment, evaporation, condensate treatment, and control into one automated process.

Conclusion:

DTRO concentrate is an unavoidable by-product of membrane-based landfill leachate treatment. DTRO can effectively separate clean water from concentrated pollutants, but the retained salts and contaminants still need a reliable final treatment route.

Landfill recirculation, off-site disposal, and advanced oxidation may have their own applications, but they do not always provide a complete solution for high-salinity concentrate.

Pretreatment and softening → MVR evaporation → mother liquor drying → condensate polishing → discharge or reuse

This integrated route can significantly reduce concentrate volume, recover water, and convert concentrated pollutants into a much smaller amount of solid or concentrated residue.

For landfill projects looking to improve the final treatment of DTRO concentrate, the key is not simply choosing an evaporator. Feedwater analysis, pretreatment, scaling control, evaporation design, condensate quality, and final residue management all need to be considered together.

With experience in industrial wastewater treatment and evaporation systems, WTEYA can develop a treatment configuration based on the actual characteristics and operating requirements of each project.