Landfill Leachate Treatment Without Membrane Concentrate: How CDOF Changes the Maths

Leachate from landfill disposal and incineration is one of the hardest streams in environmental engineering. It is high in concentration, high in toxicity, complex in composition and poor in biodegradability. Conventional processes all run into the same wall: efficiency drops, cost climbs, and the risk of secondary pollution never quite goes away.

What Makes Leachate So Difficult

Leachate forms during waste storage, landfilling or incineration through fermentation, rainwater leaching and groundwater soaking. Three characteristics create the pressure.

• Extremely high pollutant concentration. Chemical oxygen demand (COD) often reaches tens of thousands of milligrams per litre, while ammonia nitrogen (NH3-N) concentration generally exceeds 1000 mg/L, hundreds of times higher than conventional municipal wastewater.
• Complex composition and strong toxicity. The waste stream contains large amounts of hard-to-degrade organics such as aromatic hydrocarbons and halogenated compounds, plus heavy metals including chromium and lead, and various carcinogenic and cancer-promoting substances. Detectable pollutants number 70 or more.
• Very poor biodegradability. As landfills age, the BOD5/COD ratio often falls below 0.1, with hard-to-degrade organics accounting for more than 60%, which makes conventional biological treatment largely ineffective.

Untreated discharge pollutes soil and groundwater, drives water eutrophication and allows heavy metals to accumulate through the food chain.

Where the Conventional Routes Break Down

Before settling on any process, it is worth being explicit about what each conventional route does well and where it stops. The two dominant options are membrane treatment and Fenton oxidation, and both have a structural weakness rather than an incidental one.

Membrane treatment (NF/RO)

Effluent quality is acceptable, but membrane modules are prone to fouling and flux decays quickly. Frequent cleaning and replacement push up O&M costs. More critically, the process generates 15%-30% concentrate by volume of the influent, and that concentrate is hazardous waste that is difficult and costly to dispose of. Comprehensive treatment cost often exceeds 150 yuan per ton of water.

Fenton oxidation

Fenton relies on dosing large amounts of chemicals, so it is costly by design. It also generates iron sludge hazardous waste amounting to 10%-15% of the wastewater volume, which again has to be handled.

Biological treatment

A biological stage such as MBR places high demands on influent biodegradability and system stability. Where the BOD5/COD ratio has already collapsed, the biology adds residence time and tank volume without delivering reliable removal, and the effluent can be prone to re-colouring.

The CDOF Approach

CDOF is an ozone catalytic oxidation cyclonic flotation integrated technology developed by SINOKLE. Its stated advantages are full-volume treatment, a membrane-free process and zero concentrate, which directly addresses the waste-disposal weakness of the membrane route.

How it works

A dedicated catalyst converts ozone into hydroxyl radicals (OH) inside a closed pressurised reactor. With an oxidation potential as high as 2.8V, those radicals attack and cleave all kinds of hard-to-degrade organics non-selectively and rapidly, mineralising macromolecular pollutants into CO2 and H2O. Integrated cyclonic dissolved gas flotation follows in the same unit, so a proprietary separation stage lifts the oxidised material out rather than letting it settle.

Control is fully automatic through a DCS/PLC system that monitors tail gas ozone concentration, effluent ORP and pH in real time and dynamically optimises ozone dosage and reaction parameters. That closed-loop supervision is what keeps the process stable as leachate composition drifts.

Performance and economics

• Extremely fast reaction rate: effective hydraulic retention time is less than 15 minutes, only 1/6 of conventional ozone oxidation technology, which runs around 90 minutes.
• Extremely high ozone utilisation: system ozone utilisation exceeds 99.98%, and the ozone dosing ratio (O3/COD) is optimised to 0.5-1.2, only 1/5 to 1/2 of conventional technology at 2-4, reducing operating costs to 1/3-1/2 of conventional levels.
• Minimal sludge production: sludge generation across the whole process is reduced by more than 90%, easing the burden of hazardous waste disposal.
• Excellent effluent quality: efficient removal of odour and decolorisation, with colour reduced by more than 90%, leaving effluent colourless and odourless and free of re-colouring.
• Overall cost advantage: using the patented combined process of CDFU+CDOF plus biological treatment, the treatment cost per ton of water is far lower than conventional membrane plus evaporation technology.

Why the Sequence Matters

The integration is the point. A conventional train separates oxidation from separation, so each step pays its own residence time, footprint and reagent cost. Combining them inside one unit shortens the flow, keeps the oxidant working on material that has not yet been separated out, and removes the concentrate stream that would otherwise require its own disposal route.

The SINOKLE CDOF process has been applied in multiple landfill leachate treatment projects. For operators weighing a membrane route against an oxidation route, the deciding factor is usually not the effluent target, since both can meet it, but what happens to the waste that the process leaves behind. Eliminating concentrate removes an entire cost centre and a durable environmental liability at the same time.

What Changes When There Is No Concentrate

Concentrate is the hidden tax on membrane treatment. On paper the process looks clean: water passes through, contaminants stay behind, and the permeate meets its limit. In practice the contaminants that stayed behind still have to go somewhere, and the volume involved is 15%-30% of the influent. That stream needs its own disposal route, its own permits and its own budget line, and in many jurisdictions it is classified as hazardous waste.

An oxidative route that treats the full volume avoids creating that stream in the first place. Oxidation destroys rather than relocates, so the pollutants leave the system as carbon dioxide, water and a small quantity of sludge. Where the whole-flow design is applied, the process is described as full-volume treatment, and the concentrate handling equipment, storage and transport arrangements are simply not needed.

Reading the Efficiency Figures

The hydraulic retention time of under 15 minutes is worth dwelling on. Conventional ozone oxidation runs around 90 minutes, and vessels are sized accordingly, so cutting the reaction time to roughly one sixth removes a great deal of tank volume and the civil works that support it. Ozone utilisation above 99.98% matters for a different reason: ozone that does not react is ozone that was generated, paid for and then vented. High utilisation means the dosing ratio can be optimised into the narrow band of 0.5-1.2 against conventional values of 2-4, and that is where the operating cost reduction to one third or one half of conventional levels comes from.

Sludge reduction of more than 90% and colour removal above 90% complete the picture. For an operator, fewer tonnes of hazardous waste and no re-colouring of the treated water translate into fewer compliance headaches and a discharge that stays stable between sampling events.

Practical Selection Advice

Leachate composition changes as a landfill matures, so a technology choice that works early in the site's life may not hold later. Processes that depend on biological activity degrade as the BOD5/COD ratio falls below 0.1. Processes that depend on membranes accumulate concentrate. A full-volume oxidative route is less sensitive to that ageing curve, which makes it worth evaluating even where the current leachate still responds to conventional treatment.