Landfill Leachate Without Membrane Concentrate: How a CDFU and CDOF Train Removes the Brine Problem

Landfill leachate is what happens when water passes through a waste body over years and takes a little of everything with it. The result is a highly concentrated, highly toxic organic wastewater with pollutant levels that make municipal sewage look dilute: COD often in the tens of thousands of mg/L, ammonia nitrogen above 1,000 mg/L, poor biodegradability, and quality that moves with rainfall, age of the fill and the mix of waste received.

Treating it efficiently, at low cost, without creating a second pollution problem has been an open question in the industry for a long time. The mainstream answer — pretreatment, then biological treatment such as MBR, then advanced membrane treatment with nanofiltration or reverse osmosis — produces genuinely clear water. It also produces something else.

The Concentrate Is the Real Bill

Membrane treatment is a physical separation. It does not destroy pollutants; it moves them into a smaller volume of liquid. That membrane concentrate accounts for 15% to 30% of the influent, and it arrives enriched with exactly the refractory organics and salts that were hardest to deal with in the first place.

Recirculating the concentrate back into the landfill or into the front of the plant is the tempting move, and it is the one that causes salt damage and contamination of the system over time. Disposing of it by evaporation or incineration consumes a great deal of energy, with a comprehensive cost per tonne of water that often exceeds 150 yuan, and the disposal route itself carries a secondary pollution risk that has to be managed. A plant can therefore meet its discharge permit and still fail its operating budget.

Why Biological Treatment Plateaus

Biological processes are sensitive to water quality fluctuation, and leachate from an aged fill is about as fluctuating a feed as a biological system will see. The B/C ratio of aged leachate sits at 0.1-0.3, which means most of the organic matter present is not the kind bacteria can consume quickly. The stubborn macromolecular fraction passes through, and effluent COD struggles to stay below 1,000 mg/L — a figure that is no longer comfortably inside a tightening standard.

The Cost of Chemistry

Physicochemical routes such as Fenton oxidation are not bothered by water quality the way biology is, which is their appeal. They pay for that robustness in reagents, and they produce large quantities of hazardous iron sludge. High operating cost plus a hazardous waste stream makes them a poor fit for large-scale continuous treatment, even where they perform well in a batch or a pilot.

The final weakness of the conventional chain is structural. It is long, it has many stages, and every stage is a control point that can drift. Membrane modules foul, flux decays, cleaning and replacement become routine, and O&M cost rises while system reliability falls. A plant with a long chain and a fouling membrane is a plant that needs more people than its owner budgeted for.

A Process Built Without Membranes

Rather than solve the concentrate problem downstream, SINOKLE removed the step that creates it. The process is built on two units working in series: CDFU, a swirl dissolved air flotation unit, and CDOF, an integrated ozone advanced catalytic oxidation and flotation unit. Between them they deliver efficient degradation and low-carbon operation in a chain that has no membrane and therefore no concentrate.

The CDFU stage is a vertical-tank flotation unit that integrates swirl centrifugal separation, ultra-fine bubble generation and dissolved air flotation. Its job in this train is load reduction: waste oil, emulsified oil, suspended solids and other separable pollutants come out early, so the oxidation stage is not asked to burn ozone on material that could have been floated out for a fraction of the cost.

The CDOF stage is the oxidation core. The unit comprises an oxygen generation system, an ozone generation system, a high-efficiency ozone dosing system, a multi-stage catalytic reaction system and a swirl dissolved air flotation system. It integrates multi-stage ozone catalytic oxidation, hydrodynamic cavitation and swirl flotation, and it removes petroleum substances, suspended solids, colloids, COD, bacteria and a range of other pollutants quickly and at high efficiency. Because oxidation and flotation share a vessel, the floc and oxidised residue that form are separated in the same pass rather than in a downstream clarifier.

What Changes in Daily Operation

Three things change for the people running the plant. There is no concentrate to evaporate, incinerate or recirculate, which removes the single most expensive line item and the one with the worst environmental exposure. The chain is shorter, so there are fewer stages to monitor and fewer ways for the process to drift out of specification. And because the oxidation stage destroys rather than transfers, the plant is not accumulating a liability in a tank somewhere waiting for a disposal window.

What does not change is the need for realistic design. Leachate composition varies enough between sites that the ozone dose and the catalytic stage configuration have to be set from actual water, not from a template. Plants that skip that step end up with a unit that performs on the design sample and disappoints in January.

The Three Pain Points This Train Was Built For

Difficult concentrate disposal, high operating cost and difficulty in consistently meeting standards are the three failures that define leachate treatment. The CDFU plus CDOF route addresses all three directly rather than by adding another stage to the conventional chain.

For a single landfill that is a workable plant. For the wider field of difficult industrial wastewater — the streams that resist biological treatment and punish membrane systems — it is a template that can be copied, which is arguably the more useful outcome.