CDOF Process: Efficient Treatment of Landfill Leachate
I. Introduction to landfill leachate
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. According to statistics, China's annual leachate output surged from 49.546 million tonnes in 2011 to nearly 80 million tonnes in 2024, and its composition is extremely complex. Landfill leachate is highly toxic, containing more than 70 pollutants including aromatic hydrocarbons, halogenated compounds, heavy metals (chromium, lead, etc.), tumour promoters and co-carcinogens. COD is high (up to tens of thousands of mg/L) and ammonia nitrogen exceeds 1,000 mg/L — hundreds of times higher than municipal sewage. Leachate is therefore extremely harmful to the environment: without proper treatment it directly contaminates soil and groundwater, ammonia nitrogen triggers water eutrophication, and heavy metals threaten human health through the food chain.
II. Treatment technologies
As landfill sites age, the biodegradability of leachate (BOD5/COD) drops below 0.1, making conventional processes inadequate for efficient leachate treatment. Mainstream processes generally suffer from low efficiency and a high risk of secondary pollution. Membrane technologies (such as nanofiltration/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 (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 requires harsh reaction conditions (pH ≈ 3), and the 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.
III. SINOKLE CDOF CDOF process
The CDOFCDOF (integrated catalytic ozone oxidation and cyclonic dissolved gas flotation) technology independently developed by SINOKLE Technology is built around the core principles of "full-volume treatment, membrane-free and zero concentrate", completely overturning the bottlenecks of conventional processes.
CDOFSchematic of the system process flow
3.1 Technology integration multiplies efficiency
Multi-stage catalytic ozone oxidation, cyclonic centrifugal separation and dissolved gas flotation are integrated 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 a contact time shortened to 5–15 minutes (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).
3.2 Economical and environmentally friendly
A. Cost per tonne of water reduced by 50%: ozone utilisation is three times the conventional level and energy consumption is only 1/8–1/4; chemical consumption drops by 90% and hazardous sludge is sharply reduced.
B. Zero concentrate and no secondary pollution: the membrane-free design throughout the process fully mineralises pollutants, with no risk of secondary pollution.
C. Intelligent O&M: fully enclosed pressurised operation with remote monitoring support, reducing manual intervention by 70%.
D. Small footprint: highly integrated and skid-mounted equipment with a short flow and small footprint.
E. Colourless and odourless: efficient removal of odour and colour (colour reduced by more than 90%).
IV. CDOFCDOF Engineering applications
SINOKLE CDOFCDOF process offers high reaction efficiency (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. Looking ahead, SINOKLE will continue to deepen its work in advanced oxidation, returning every drop of leachate to clarity and safeguarding the lasting flow of groundwater.
