Landfill Leachate Without Membranes: How CDOF Catalytic Ozone Oxidation Cuts Concentrate, Sludge and Cost
Landfill leachate is a high-concentration organic wastewater formed during the stacking and landfilling of waste at landfill sites or incineration plants, through waste fermentation, rainwater washing and groundwater soaking. The scale of the problem keeps growing: China's annual leachate output surged from 49.546 million tonnes in 2011 to nearly 80 million tonnes in 2024, and the composition is extremely complex. The liquid is highly toxic, containing more than 70 pollutants including aromatic hydrocarbons, halogenated compounds, heavy metals such as chromium and lead, tumour promoters and co-carcinogens.
The numbers behind the toxicity are stark. COD runs up to tens of thousands of mg/L, and ammonia nitrogen exceeds 1,000 mg/L - hundreds of times higher than municipal sewage. Without proper treatment, leachate directly contaminates soil and groundwater, the ammonia nitrogen triggers water eutrophication, and heavy metals threaten human health through the food chain.
Why Aging Sites Break Conventional Processes
As landfill sites age, the biodegradability of leachate - the BOD5/COD ratio - drops below 0.1, and conventional processes become inadequate for efficient treatment. The mainstream options each carry a structural penalty.
Membrane technologies such as nanofiltration and reverse osmosis produce stable effluent in the short term, but suffer severe membrane fouling, sharp flux decline and costly frequent replacement. They also generate 15%-30% concentrate classified as hazardous waste requiring secondary treatment, with actual costs exceeding RMB 100 per tonne. The Fenton oxidation process relies on large amounts of chemicals and generates 10%-15% iron sludge - also hazardous waste that is difficult to dispose of. Moreover, Fenton demands harsh reaction conditions around pH 3, and its effluent tends to regain colour, with poor stability. Biological processes such as MBR demand high biodegradability, while refractory organics account for more than 60% in aged leachate, so effluent COD often exceeds 1,000 mg/L and fails to meet standards.
The CDOF Proposition: Full-Volume, Membrane-Free, Zero Concentrate
The CDOF technology - integrated catalytic ozone oxidation and cyclonic dissolved gas flotation - independently developed by SINOKLE Technology is built around three core principles: full-volume treatment, membrane-free operation and zero concentrate. It was designed to overturn the bottlenecks above rather than patch them.
The integration is what multiplies efficiency. Multi-stage catalytic ozone oxidation, cyclonic centrifugal separation and dissolved gas flotation are combined into a single skid-mounted unit, increasing the reaction rate 100-fold. Ozone forms ultra-fine nanobubbles under pressurised swirling, with a dispersion degree more than 100 times that of conventional aeration, and the contact time is shortened to 5-15 minutes where conventional processes need 60-120 minutes. A proprietary catalyst modified by atomic deposition rapidly activates ozone to generate ·OH radicals that oxidise refractory organics non-selectively. In addition, ozone oxidises ammonia nitrogen to nitrogen gas, while cyclonic flotation efficiently strips suspended solids, giving effluent colour ≤30 - colourless and odourless.
The Economics, Line by Line
Cost per tonne of water drops by 50%: ozone utilisation reaches three times the conventional level, energy consumption is only 1/8 to 1/4, chemical consumption falls by 90%, and hazardous sludge is sharply reduced. The membrane-free design fully mineralises pollutants, so there is no concentrate stream and no risk of secondary pollution. Intelligent O&M keeps the fully enclosed pressurised system under remote monitoring, reducing manual intervention by 70%. The highly integrated skid-mounted equipment keeps the flow short and the footprint small, and odour and colour removal exceeds 90%.
Engineering Record and Outlook
The engineering record matches the laboratory figures: the process offers a high reaction efficiency with HRT ≤5 min, low operating costs and zero hazardous waste discharge. By 2025 the technology had achieved long-term stable operation in multiple hazardous waste and incineration projects across China, becoming a key technical support for zero-waste city development. SINOKLE continues to deepen its work in advanced oxidation - with the aim of returning every drop of leachate to clarity and safeguarding the lasting flow of groundwater.
Reading the Waste Stream Correctly
Part of the CDOF advantage comes from treating leachate as what it is: a young wastewater that simply refuses to behave like one. Fresh leachate carries the fermentation products of recently buried waste; old leachate carries what decades of slow chemistry have left behind - long-chain organics, humic substances and the metals that biological processes concentrate but never destroy. A process that only works on the biodegradable fraction therefore works less and less every year a landfill ages, which is exactly the trajectory the BOD5/COD ratio describes. Oxidation is the only mainstream mechanism whose effectiveness does not depend on that ratio, because ·OH radicals attack the molecular structure directly rather than waiting for biology to find it edible.
The zero-concentrate principle closes the loop. Every concentrate-producing route eventually has to decide where its rejected 15%-30% goes - back into the landfill, into evaporation ponds, or into an ever-growing hazardous waste bill. By mineralising pollutants in the main stream instead of rejecting them into a side stream, the CDOF route removes that decision entirely, which is why the cost comparison with membrane routes holds up even before the RMB 100 per tonne concentrate charge is counted.